![Tycho Andersen](/assets/img/avatar_default.png)
This patch is the first step in enabling checkpoint/restore of processes with seccomp enabled. One of the things CRIU does while dumping tasks is inject code into them via ptrace to collect information that is only available to the process itself. However, if we are in a seccomp mode where these processes are prohibited from making these syscalls, then what CRIU does kills the task. This patch adds a new ptrace option, PTRACE_O_SUSPEND_SECCOMP, that enables a task from the init user namespace which has CAP_SYS_ADMIN and no seccomp filters to disable (and re-enable) seccomp filters for another task so that they can be successfully dumped (and restored). We restrict the set of processes that can disable seccomp through ptrace because although today ptrace can be used to bypass seccomp, there is some discussion of closing this loophole in the future and we would like this patch to not depend on that behavior and be future proofed for when it is removed. Note that seccomp can be suspended before any filters are actually installed; this behavior is useful on criu restore, so that we can suspend seccomp, restore the filters, unmap our restore code from the restored process' address space, and then resume the task by detaching and have the filters resumed as well. v2 changes: * require that the tracer have no seccomp filters installed * drop TIF_NOTSC manipulation from the patch * change from ptrace command to a ptrace option and use this ptrace option as the flag to check. This means that as soon as the tracer detaches/dies, seccomp is re-enabled and as a corrollary that one can not disable seccomp across PTRACE_ATTACHs. v3 changes: * get rid of various #ifdefs everywhere * report more sensible errors when PTRACE_O_SUSPEND_SECCOMP is incorrectly used v4 changes: * get rid of may_suspend_seccomp() in favor of a capable() check in ptrace directly v5 changes: * check that seccomp is not enabled (or suspended) on the tracer Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com> CC: Will Drewry <wad@chromium.org> CC: Roland McGrath <roland@hack.frob.com> CC: Pavel Emelyanov <xemul@parallels.com> CC: Serge E. Hallyn <serge.hallyn@ubuntu.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Andy Lutomirski <luto@amacapital.net> [kees: access seccomp.mode through seccomp_mode() instead] Signed-off-by: Kees Cook <keescook@chromium.org>
388 lines
14 KiB
C
388 lines
14 KiB
C
#ifndef _LINUX_PTRACE_H
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#define _LINUX_PTRACE_H
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#include <linux/compiler.h> /* For unlikely. */
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#include <linux/sched.h> /* For struct task_struct. */
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#include <linux/err.h> /* for IS_ERR_VALUE */
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#include <linux/bug.h> /* For BUG_ON. */
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#include <linux/pid_namespace.h> /* For task_active_pid_ns. */
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#include <uapi/linux/ptrace.h>
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/*
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* Ptrace flags
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*
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* The owner ship rules for task->ptrace which holds the ptrace
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* flags is simple. When a task is running it owns it's task->ptrace
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* flags. When the a task is stopped the ptracer owns task->ptrace.
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*/
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#define PT_SEIZED 0x00010000 /* SEIZE used, enable new behavior */
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#define PT_PTRACED 0x00000001
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#define PT_DTRACE 0x00000002 /* delayed trace (used on m68k, i386) */
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#define PT_PTRACE_CAP 0x00000004 /* ptracer can follow suid-exec */
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#define PT_OPT_FLAG_SHIFT 3
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/* PT_TRACE_* event enable flags */
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#define PT_EVENT_FLAG(event) (1 << (PT_OPT_FLAG_SHIFT + (event)))
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#define PT_TRACESYSGOOD PT_EVENT_FLAG(0)
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#define PT_TRACE_FORK PT_EVENT_FLAG(PTRACE_EVENT_FORK)
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#define PT_TRACE_VFORK PT_EVENT_FLAG(PTRACE_EVENT_VFORK)
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#define PT_TRACE_CLONE PT_EVENT_FLAG(PTRACE_EVENT_CLONE)
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#define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC)
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#define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE)
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#define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT)
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#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)
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#define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT)
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#define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT)
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/* single stepping state bits (used on ARM and PA-RISC) */
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#define PT_SINGLESTEP_BIT 31
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#define PT_SINGLESTEP (1<<PT_SINGLESTEP_BIT)
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#define PT_BLOCKSTEP_BIT 30
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#define PT_BLOCKSTEP (1<<PT_BLOCKSTEP_BIT)
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extern long arch_ptrace(struct task_struct *child, long request,
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unsigned long addr, unsigned long data);
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extern int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len);
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extern int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len);
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extern void ptrace_disable(struct task_struct *);
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extern int ptrace_request(struct task_struct *child, long request,
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unsigned long addr, unsigned long data);
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extern void ptrace_notify(int exit_code);
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extern void __ptrace_link(struct task_struct *child,
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struct task_struct *new_parent);
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extern void __ptrace_unlink(struct task_struct *child);
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extern void exit_ptrace(struct task_struct *tracer, struct list_head *dead);
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#define PTRACE_MODE_READ 0x01
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#define PTRACE_MODE_ATTACH 0x02
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#define PTRACE_MODE_NOAUDIT 0x04
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/* Returns true on success, false on denial. */
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extern bool ptrace_may_access(struct task_struct *task, unsigned int mode);
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static inline int ptrace_reparented(struct task_struct *child)
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{
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return !same_thread_group(child->real_parent, child->parent);
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}
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static inline void ptrace_unlink(struct task_struct *child)
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{
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if (unlikely(child->ptrace))
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__ptrace_unlink(child);
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}
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int generic_ptrace_peekdata(struct task_struct *tsk, unsigned long addr,
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unsigned long data);
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int generic_ptrace_pokedata(struct task_struct *tsk, unsigned long addr,
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unsigned long data);
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/**
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* ptrace_parent - return the task that is tracing the given task
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* @task: task to consider
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*
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* Returns %NULL if no one is tracing @task, or the &struct task_struct
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* pointer to its tracer.
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*
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* Must called under rcu_read_lock(). The pointer returned might be kept
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* live only by RCU. During exec, this may be called with task_lock() held
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* on @task, still held from when check_unsafe_exec() was called.
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*/
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static inline struct task_struct *ptrace_parent(struct task_struct *task)
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{
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if (unlikely(task->ptrace))
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return rcu_dereference(task->parent);
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return NULL;
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}
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/**
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* ptrace_event_enabled - test whether a ptrace event is enabled
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* @task: ptracee of interest
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* @event: %PTRACE_EVENT_* to test
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*
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* Test whether @event is enabled for ptracee @task.
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*
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* Returns %true if @event is enabled, %false otherwise.
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*/
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static inline bool ptrace_event_enabled(struct task_struct *task, int event)
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{
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return task->ptrace & PT_EVENT_FLAG(event);
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}
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/**
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* ptrace_event - possibly stop for a ptrace event notification
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* @event: %PTRACE_EVENT_* value to report
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* @message: value for %PTRACE_GETEVENTMSG to return
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*
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* Check whether @event is enabled and, if so, report @event and @message
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* to the ptrace parent.
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*
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* Called without locks.
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*/
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static inline void ptrace_event(int event, unsigned long message)
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{
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if (unlikely(ptrace_event_enabled(current, event))) {
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current->ptrace_message = message;
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ptrace_notify((event << 8) | SIGTRAP);
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} else if (event == PTRACE_EVENT_EXEC) {
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/* legacy EXEC report via SIGTRAP */
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if ((current->ptrace & (PT_PTRACED|PT_SEIZED)) == PT_PTRACED)
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send_sig(SIGTRAP, current, 0);
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}
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}
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/**
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* ptrace_event_pid - possibly stop for a ptrace event notification
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* @event: %PTRACE_EVENT_* value to report
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* @pid: process identifier for %PTRACE_GETEVENTMSG to return
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*
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* Check whether @event is enabled and, if so, report @event and @pid
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* to the ptrace parent. @pid is reported as the pid_t seen from the
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* the ptrace parent's pid namespace.
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*
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* Called without locks.
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*/
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static inline void ptrace_event_pid(int event, struct pid *pid)
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{
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/*
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* FIXME: There's a potential race if a ptracer in a different pid
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* namespace than parent attaches between computing message below and
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* when we acquire tasklist_lock in ptrace_stop(). If this happens,
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* the ptracer will get a bogus pid from PTRACE_GETEVENTMSG.
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*/
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unsigned long message = 0;
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struct pid_namespace *ns;
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rcu_read_lock();
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ns = task_active_pid_ns(rcu_dereference(current->parent));
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if (ns)
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message = pid_nr_ns(pid, ns);
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rcu_read_unlock();
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ptrace_event(event, message);
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}
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/**
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* ptrace_init_task - initialize ptrace state for a new child
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* @child: new child task
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* @ptrace: true if child should be ptrace'd by parent's tracer
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*
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* This is called immediately after adding @child to its parent's children
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* list. @ptrace is false in the normal case, and true to ptrace @child.
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*
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* Called with current's siglock and write_lock_irq(&tasklist_lock) held.
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*/
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static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
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{
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INIT_LIST_HEAD(&child->ptrace_entry);
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INIT_LIST_HEAD(&child->ptraced);
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child->jobctl = 0;
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child->ptrace = 0;
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child->parent = child->real_parent;
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if (unlikely(ptrace) && current->ptrace) {
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child->ptrace = current->ptrace;
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__ptrace_link(child, current->parent);
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if (child->ptrace & PT_SEIZED)
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task_set_jobctl_pending(child, JOBCTL_TRAP_STOP);
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else
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sigaddset(&child->pending.signal, SIGSTOP);
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set_tsk_thread_flag(child, TIF_SIGPENDING);
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}
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}
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/**
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* ptrace_release_task - final ptrace-related cleanup of a zombie being reaped
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* @task: task in %EXIT_DEAD state
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*
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* Called with write_lock(&tasklist_lock) held.
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*/
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static inline void ptrace_release_task(struct task_struct *task)
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{
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BUG_ON(!list_empty(&task->ptraced));
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ptrace_unlink(task);
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BUG_ON(!list_empty(&task->ptrace_entry));
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}
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#ifndef force_successful_syscall_return
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/*
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* System call handlers that, upon successful completion, need to return a
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* negative value should call force_successful_syscall_return() right before
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* returning. On architectures where the syscall convention provides for a
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* separate error flag (e.g., alpha, ia64, ppc{,64}, sparc{,64}, possibly
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* others), this macro can be used to ensure that the error flag will not get
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* set. On architectures which do not support a separate error flag, the macro
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* is a no-op and the spurious error condition needs to be filtered out by some
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* other means (e.g., in user-level, by passing an extra argument to the
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* syscall handler, or something along those lines).
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*/
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#define force_successful_syscall_return() do { } while (0)
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#endif
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#ifndef is_syscall_success
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/*
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* On most systems we can tell if a syscall is a success based on if the retval
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* is an error value. On some systems like ia64 and powerpc they have different
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* indicators of success/failure and must define their own.
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*/
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#define is_syscall_success(regs) (!IS_ERR_VALUE((unsigned long)(regs_return_value(regs))))
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#endif
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/*
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* <asm/ptrace.h> should define the following things inside #ifdef __KERNEL__.
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*
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* These do-nothing inlines are used when the arch does not
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* implement single-step. The kerneldoc comments are here
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* to document the interface for all arch definitions.
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*/
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#ifndef arch_has_single_step
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/**
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* arch_has_single_step - does this CPU support user-mode single-step?
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*
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* If this is defined, then there must be function declarations or
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* inlines for user_enable_single_step() and user_disable_single_step().
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* arch_has_single_step() should evaluate to nonzero iff the machine
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* supports instruction single-step for user mode.
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* It can be a constant or it can test a CPU feature bit.
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*/
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#define arch_has_single_step() (0)
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/**
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* user_enable_single_step - single-step in user-mode task
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* @task: either current or a task stopped in %TASK_TRACED
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*
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* This can only be called when arch_has_single_step() has returned nonzero.
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* Set @task so that when it returns to user mode, it will trap after the
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* next single instruction executes. If arch_has_block_step() is defined,
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* this must clear the effects of user_enable_block_step() too.
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*/
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static inline void user_enable_single_step(struct task_struct *task)
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{
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BUG(); /* This can never be called. */
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}
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/**
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* user_disable_single_step - cancel user-mode single-step
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* @task: either current or a task stopped in %TASK_TRACED
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*
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* Clear @task of the effects of user_enable_single_step() and
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* user_enable_block_step(). This can be called whether or not either
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* of those was ever called on @task, and even if arch_has_single_step()
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* returned zero.
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*/
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static inline void user_disable_single_step(struct task_struct *task)
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{
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}
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#else
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extern void user_enable_single_step(struct task_struct *);
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extern void user_disable_single_step(struct task_struct *);
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#endif /* arch_has_single_step */
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#ifndef arch_has_block_step
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/**
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* arch_has_block_step - does this CPU support user-mode block-step?
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*
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* If this is defined, then there must be a function declaration or inline
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* for user_enable_block_step(), and arch_has_single_step() must be defined
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* too. arch_has_block_step() should evaluate to nonzero iff the machine
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* supports step-until-branch for user mode. It can be a constant or it
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* can test a CPU feature bit.
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*/
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#define arch_has_block_step() (0)
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/**
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* user_enable_block_step - step until branch in user-mode task
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* @task: either current or a task stopped in %TASK_TRACED
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*
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* This can only be called when arch_has_block_step() has returned nonzero,
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* and will never be called when single-instruction stepping is being used.
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* Set @task so that when it returns to user mode, it will trap after the
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* next branch or trap taken.
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*/
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static inline void user_enable_block_step(struct task_struct *task)
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{
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BUG(); /* This can never be called. */
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}
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#else
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extern void user_enable_block_step(struct task_struct *);
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#endif /* arch_has_block_step */
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#ifdef ARCH_HAS_USER_SINGLE_STEP_INFO
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extern void user_single_step_siginfo(struct task_struct *tsk,
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struct pt_regs *regs, siginfo_t *info);
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#else
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static inline void user_single_step_siginfo(struct task_struct *tsk,
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struct pt_regs *regs, siginfo_t *info)
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{
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memset(info, 0, sizeof(*info));
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info->si_signo = SIGTRAP;
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}
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#endif
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#ifndef arch_ptrace_stop_needed
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/**
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* arch_ptrace_stop_needed - Decide whether arch_ptrace_stop() should be called
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* @code: current->exit_code value ptrace will stop with
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* @info: siginfo_t pointer (or %NULL) for signal ptrace will stop with
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*
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* This is called with the siglock held, to decide whether or not it's
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* necessary to release the siglock and call arch_ptrace_stop() with the
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* same @code and @info arguments. It can be defined to a constant if
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* arch_ptrace_stop() is never required, or always is. On machines where
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* this makes sense, it should be defined to a quick test to optimize out
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* calling arch_ptrace_stop() when it would be superfluous. For example,
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* if the thread has not been back to user mode since the last stop, the
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* thread state might indicate that nothing needs to be done.
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*
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* This is guaranteed to be invoked once before a task stops for ptrace and
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* may include arch-specific operations necessary prior to a ptrace stop.
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*/
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#define arch_ptrace_stop_needed(code, info) (0)
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#endif
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#ifndef arch_ptrace_stop
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/**
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* arch_ptrace_stop - Do machine-specific work before stopping for ptrace
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* @code: current->exit_code value ptrace will stop with
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* @info: siginfo_t pointer (or %NULL) for signal ptrace will stop with
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*
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* This is called with no locks held when arch_ptrace_stop_needed() has
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* just returned nonzero. It is allowed to block, e.g. for user memory
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* access. The arch can have machine-specific work to be done before
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* ptrace stops. On ia64, register backing store gets written back to user
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* memory here. Since this can be costly (requires dropping the siglock),
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* we only do it when the arch requires it for this particular stop, as
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* indicated by arch_ptrace_stop_needed().
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*/
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#define arch_ptrace_stop(code, info) do { } while (0)
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#endif
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#ifndef current_pt_regs
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#define current_pt_regs() task_pt_regs(current)
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#endif
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#ifndef ptrace_signal_deliver
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#define ptrace_signal_deliver() ((void)0)
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#endif
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/*
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* unlike current_pt_regs(), this one is equal to task_pt_regs(current)
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* on *all* architectures; the only reason to have a per-arch definition
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* is optimisation.
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*/
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#ifndef signal_pt_regs
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#define signal_pt_regs() task_pt_regs(current)
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#endif
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#ifndef current_user_stack_pointer
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#define current_user_stack_pointer() user_stack_pointer(current_pt_regs())
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#endif
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extern int task_current_syscall(struct task_struct *target, long *callno,
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unsigned long args[6], unsigned int maxargs,
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unsigned long *sp, unsigned long *pc);
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#endif
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