![Alexei Starovoitov](/assets/img/avatar_default.png)
clean up names related to socket filtering and bpf in the following way: - everything that deals with sockets keeps 'sk_*' prefix - everything that is pure BPF is changed to 'bpf_*' prefix split 'struct sk_filter' into struct sk_filter { atomic_t refcnt; struct rcu_head rcu; struct bpf_prog *prog; }; and struct bpf_prog { u32 jited:1, len:31; struct sock_fprog_kern *orig_prog; unsigned int (*bpf_func)(const struct sk_buff *skb, const struct bpf_insn *filter); union { struct sock_filter insns[0]; struct bpf_insn insnsi[0]; struct work_struct work; }; }; so that 'struct bpf_prog' can be used independent of sockets and cleans up 'unattached' bpf use cases split SK_RUN_FILTER macro into: SK_RUN_FILTER to be used with 'struct sk_filter *' and BPF_PROG_RUN to be used with 'struct bpf_prog *' __sk_filter_release(struct sk_filter *) gains __bpf_prog_release(struct bpf_prog *) helper function also perform related renames for the functions that work with 'struct bpf_prog *', since they're on the same lines: sk_filter_size -> bpf_prog_size sk_filter_select_runtime -> bpf_prog_select_runtime sk_filter_free -> bpf_prog_free sk_unattached_filter_create -> bpf_prog_create sk_unattached_filter_destroy -> bpf_prog_destroy sk_store_orig_filter -> bpf_prog_store_orig_filter sk_release_orig_filter -> bpf_release_orig_filter __sk_migrate_filter -> bpf_migrate_filter __sk_prepare_filter -> bpf_prepare_filter API for attaching classic BPF to a socket stays the same: sk_attach_filter(prog, struct sock *)/sk_detach_filter(struct sock *) and SK_RUN_FILTER(struct sk_filter *, ctx) to execute a program which is used by sockets, tun, af_packet API for 'unattached' BPF programs becomes: bpf_prog_create(struct bpf_prog **)/bpf_prog_destroy(struct bpf_prog *) and BPF_PROG_RUN(struct bpf_prog *, ctx) to execute a program which is used by isdn, ppp, team, seccomp, ptp, xt_bpf, cls_bpf, test_bpf Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
520 lines
14 KiB
C
520 lines
14 KiB
C
/*
|
|
* linux/kernel/seccomp.c
|
|
*
|
|
* Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com>
|
|
*
|
|
* Copyright (C) 2012 Google, Inc.
|
|
* Will Drewry <wad@chromium.org>
|
|
*
|
|
* This defines a simple but solid secure-computing facility.
|
|
*
|
|
* Mode 1 uses a fixed list of allowed system calls.
|
|
* Mode 2 allows user-defined system call filters in the form
|
|
* of Berkeley Packet Filters/Linux Socket Filters.
|
|
*/
|
|
|
|
#include <linux/atomic.h>
|
|
#include <linux/audit.h>
|
|
#include <linux/compat.h>
|
|
#include <linux/sched.h>
|
|
#include <linux/seccomp.h>
|
|
|
|
/* #define SECCOMP_DEBUG 1 */
|
|
|
|
#ifdef CONFIG_SECCOMP_FILTER
|
|
#include <asm/syscall.h>
|
|
#include <linux/filter.h>
|
|
#include <linux/ptrace.h>
|
|
#include <linux/security.h>
|
|
#include <linux/slab.h>
|
|
#include <linux/tracehook.h>
|
|
#include <linux/uaccess.h>
|
|
|
|
/**
|
|
* struct seccomp_filter - container for seccomp BPF programs
|
|
*
|
|
* @usage: reference count to manage the object lifetime.
|
|
* get/put helpers should be used when accessing an instance
|
|
* outside of a lifetime-guarded section. In general, this
|
|
* is only needed for handling filters shared across tasks.
|
|
* @prev: points to a previously installed, or inherited, filter
|
|
* @len: the number of instructions in the program
|
|
* @insnsi: the BPF program instructions to evaluate
|
|
*
|
|
* seccomp_filter objects are organized in a tree linked via the @prev
|
|
* pointer. For any task, it appears to be a singly-linked list starting
|
|
* with current->seccomp.filter, the most recently attached or inherited filter.
|
|
* However, multiple filters may share a @prev node, by way of fork(), which
|
|
* results in a unidirectional tree existing in memory. This is similar to
|
|
* how namespaces work.
|
|
*
|
|
* seccomp_filter objects should never be modified after being attached
|
|
* to a task_struct (other than @usage).
|
|
*/
|
|
struct seccomp_filter {
|
|
atomic_t usage;
|
|
struct seccomp_filter *prev;
|
|
struct bpf_prog *prog;
|
|
};
|
|
|
|
/* Limit any path through the tree to 256KB worth of instructions. */
|
|
#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
|
|
|
|
/*
|
|
* Endianness is explicitly ignored and left for BPF program authors to manage
|
|
* as per the specific architecture.
|
|
*/
|
|
static void populate_seccomp_data(struct seccomp_data *sd)
|
|
{
|
|
struct task_struct *task = current;
|
|
struct pt_regs *regs = task_pt_regs(task);
|
|
unsigned long args[6];
|
|
|
|
sd->nr = syscall_get_nr(task, regs);
|
|
sd->arch = syscall_get_arch();
|
|
syscall_get_arguments(task, regs, 0, 6, args);
|
|
sd->args[0] = args[0];
|
|
sd->args[1] = args[1];
|
|
sd->args[2] = args[2];
|
|
sd->args[3] = args[3];
|
|
sd->args[4] = args[4];
|
|
sd->args[5] = args[5];
|
|
sd->instruction_pointer = KSTK_EIP(task);
|
|
}
|
|
|
|
/**
|
|
* seccomp_check_filter - verify seccomp filter code
|
|
* @filter: filter to verify
|
|
* @flen: length of filter
|
|
*
|
|
* Takes a previously checked filter (by bpf_check_classic) and
|
|
* redirects all filter code that loads struct sk_buff data
|
|
* and related data through seccomp_bpf_load. It also
|
|
* enforces length and alignment checking of those loads.
|
|
*
|
|
* Returns 0 if the rule set is legal or -EINVAL if not.
|
|
*/
|
|
static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
|
|
{
|
|
int pc;
|
|
for (pc = 0; pc < flen; pc++) {
|
|
struct sock_filter *ftest = &filter[pc];
|
|
u16 code = ftest->code;
|
|
u32 k = ftest->k;
|
|
|
|
switch (code) {
|
|
case BPF_LD | BPF_W | BPF_ABS:
|
|
ftest->code = BPF_LDX | BPF_W | BPF_ABS;
|
|
/* 32-bit aligned and not out of bounds. */
|
|
if (k >= sizeof(struct seccomp_data) || k & 3)
|
|
return -EINVAL;
|
|
continue;
|
|
case BPF_LD | BPF_W | BPF_LEN:
|
|
ftest->code = BPF_LD | BPF_IMM;
|
|
ftest->k = sizeof(struct seccomp_data);
|
|
continue;
|
|
case BPF_LDX | BPF_W | BPF_LEN:
|
|
ftest->code = BPF_LDX | BPF_IMM;
|
|
ftest->k = sizeof(struct seccomp_data);
|
|
continue;
|
|
/* Explicitly include allowed calls. */
|
|
case BPF_RET | BPF_K:
|
|
case BPF_RET | BPF_A:
|
|
case BPF_ALU | BPF_ADD | BPF_K:
|
|
case BPF_ALU | BPF_ADD | BPF_X:
|
|
case BPF_ALU | BPF_SUB | BPF_K:
|
|
case BPF_ALU | BPF_SUB | BPF_X:
|
|
case BPF_ALU | BPF_MUL | BPF_K:
|
|
case BPF_ALU | BPF_MUL | BPF_X:
|
|
case BPF_ALU | BPF_DIV | BPF_K:
|
|
case BPF_ALU | BPF_DIV | BPF_X:
|
|
case BPF_ALU | BPF_AND | BPF_K:
|
|
case BPF_ALU | BPF_AND | BPF_X:
|
|
case BPF_ALU | BPF_OR | BPF_K:
|
|
case BPF_ALU | BPF_OR | BPF_X:
|
|
case BPF_ALU | BPF_XOR | BPF_K:
|
|
case BPF_ALU | BPF_XOR | BPF_X:
|
|
case BPF_ALU | BPF_LSH | BPF_K:
|
|
case BPF_ALU | BPF_LSH | BPF_X:
|
|
case BPF_ALU | BPF_RSH | BPF_K:
|
|
case BPF_ALU | BPF_RSH | BPF_X:
|
|
case BPF_ALU | BPF_NEG:
|
|
case BPF_LD | BPF_IMM:
|
|
case BPF_LDX | BPF_IMM:
|
|
case BPF_MISC | BPF_TAX:
|
|
case BPF_MISC | BPF_TXA:
|
|
case BPF_LD | BPF_MEM:
|
|
case BPF_LDX | BPF_MEM:
|
|
case BPF_ST:
|
|
case BPF_STX:
|
|
case BPF_JMP | BPF_JA:
|
|
case BPF_JMP | BPF_JEQ | BPF_K:
|
|
case BPF_JMP | BPF_JEQ | BPF_X:
|
|
case BPF_JMP | BPF_JGE | BPF_K:
|
|
case BPF_JMP | BPF_JGE | BPF_X:
|
|
case BPF_JMP | BPF_JGT | BPF_K:
|
|
case BPF_JMP | BPF_JGT | BPF_X:
|
|
case BPF_JMP | BPF_JSET | BPF_K:
|
|
case BPF_JMP | BPF_JSET | BPF_X:
|
|
continue;
|
|
default:
|
|
return -EINVAL;
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* seccomp_run_filters - evaluates all seccomp filters against @syscall
|
|
* @syscall: number of the current system call
|
|
*
|
|
* Returns valid seccomp BPF response codes.
|
|
*/
|
|
static u32 seccomp_run_filters(int syscall)
|
|
{
|
|
struct seccomp_filter *f;
|
|
struct seccomp_data sd;
|
|
u32 ret = SECCOMP_RET_ALLOW;
|
|
|
|
/* Ensure unexpected behavior doesn't result in failing open. */
|
|
if (WARN_ON(current->seccomp.filter == NULL))
|
|
return SECCOMP_RET_KILL;
|
|
|
|
populate_seccomp_data(&sd);
|
|
|
|
/*
|
|
* All filters in the list are evaluated and the lowest BPF return
|
|
* value always takes priority (ignoring the DATA).
|
|
*/
|
|
for (f = current->seccomp.filter; f; f = f->prev) {
|
|
u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)&sd);
|
|
|
|
if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
|
|
ret = cur_ret;
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* seccomp_attach_filter: Attaches a seccomp filter to current.
|
|
* @fprog: BPF program to install
|
|
*
|
|
* Returns 0 on success or an errno on failure.
|
|
*/
|
|
static long seccomp_attach_filter(struct sock_fprog *fprog)
|
|
{
|
|
struct seccomp_filter *filter;
|
|
unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
|
|
unsigned long total_insns = fprog->len;
|
|
struct sock_filter *fp;
|
|
int new_len;
|
|
long ret;
|
|
|
|
if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
|
|
return -EINVAL;
|
|
|
|
for (filter = current->seccomp.filter; filter; filter = filter->prev)
|
|
total_insns += filter->prog->len + 4; /* include a 4 instr penalty */
|
|
if (total_insns > MAX_INSNS_PER_PATH)
|
|
return -ENOMEM;
|
|
|
|
/*
|
|
* Installing a seccomp filter requires that the task has
|
|
* CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
|
|
* This avoids scenarios where unprivileged tasks can affect the
|
|
* behavior of privileged children.
|
|
*/
|
|
if (!current->no_new_privs &&
|
|
security_capable_noaudit(current_cred(), current_user_ns(),
|
|
CAP_SYS_ADMIN) != 0)
|
|
return -EACCES;
|
|
|
|
fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN);
|
|
if (!fp)
|
|
return -ENOMEM;
|
|
|
|
/* Copy the instructions from fprog. */
|
|
ret = -EFAULT;
|
|
if (copy_from_user(fp, fprog->filter, fp_size))
|
|
goto free_prog;
|
|
|
|
/* Check and rewrite the fprog via the skb checker */
|
|
ret = bpf_check_classic(fp, fprog->len);
|
|
if (ret)
|
|
goto free_prog;
|
|
|
|
/* Check and rewrite the fprog for seccomp use */
|
|
ret = seccomp_check_filter(fp, fprog->len);
|
|
if (ret)
|
|
goto free_prog;
|
|
|
|
/* Convert 'sock_filter' insns to 'bpf_insn' insns */
|
|
ret = bpf_convert_filter(fp, fprog->len, NULL, &new_len);
|
|
if (ret)
|
|
goto free_prog;
|
|
|
|
/* Allocate a new seccomp_filter */
|
|
ret = -ENOMEM;
|
|
filter = kzalloc(sizeof(struct seccomp_filter),
|
|
GFP_KERNEL|__GFP_NOWARN);
|
|
if (!filter)
|
|
goto free_prog;
|
|
|
|
filter->prog = kzalloc(bpf_prog_size(new_len),
|
|
GFP_KERNEL|__GFP_NOWARN);
|
|
if (!filter->prog)
|
|
goto free_filter;
|
|
|
|
ret = bpf_convert_filter(fp, fprog->len, filter->prog->insnsi, &new_len);
|
|
if (ret)
|
|
goto free_filter_prog;
|
|
kfree(fp);
|
|
|
|
atomic_set(&filter->usage, 1);
|
|
filter->prog->len = new_len;
|
|
|
|
bpf_prog_select_runtime(filter->prog);
|
|
|
|
/*
|
|
* If there is an existing filter, make it the prev and don't drop its
|
|
* task reference.
|
|
*/
|
|
filter->prev = current->seccomp.filter;
|
|
current->seccomp.filter = filter;
|
|
return 0;
|
|
|
|
free_filter_prog:
|
|
kfree(filter->prog);
|
|
free_filter:
|
|
kfree(filter);
|
|
free_prog:
|
|
kfree(fp);
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* seccomp_attach_user_filter - attaches a user-supplied sock_fprog
|
|
* @user_filter: pointer to the user data containing a sock_fprog.
|
|
*
|
|
* Returns 0 on success and non-zero otherwise.
|
|
*/
|
|
static long seccomp_attach_user_filter(char __user *user_filter)
|
|
{
|
|
struct sock_fprog fprog;
|
|
long ret = -EFAULT;
|
|
|
|
#ifdef CONFIG_COMPAT
|
|
if (is_compat_task()) {
|
|
struct compat_sock_fprog fprog32;
|
|
if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
|
|
goto out;
|
|
fprog.len = fprog32.len;
|
|
fprog.filter = compat_ptr(fprog32.filter);
|
|
} else /* falls through to the if below. */
|
|
#endif
|
|
if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
|
|
goto out;
|
|
ret = seccomp_attach_filter(&fprog);
|
|
out:
|
|
return ret;
|
|
}
|
|
|
|
/* get_seccomp_filter - increments the reference count of the filter on @tsk */
|
|
void get_seccomp_filter(struct task_struct *tsk)
|
|
{
|
|
struct seccomp_filter *orig = tsk->seccomp.filter;
|
|
if (!orig)
|
|
return;
|
|
/* Reference count is bounded by the number of total processes. */
|
|
atomic_inc(&orig->usage);
|
|
}
|
|
|
|
/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
|
|
void put_seccomp_filter(struct task_struct *tsk)
|
|
{
|
|
struct seccomp_filter *orig = tsk->seccomp.filter;
|
|
/* Clean up single-reference branches iteratively. */
|
|
while (orig && atomic_dec_and_test(&orig->usage)) {
|
|
struct seccomp_filter *freeme = orig;
|
|
orig = orig->prev;
|
|
bpf_prog_free(freeme->prog);
|
|
kfree(freeme);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* seccomp_send_sigsys - signals the task to allow in-process syscall emulation
|
|
* @syscall: syscall number to send to userland
|
|
* @reason: filter-supplied reason code to send to userland (via si_errno)
|
|
*
|
|
* Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
|
|
*/
|
|
static void seccomp_send_sigsys(int syscall, int reason)
|
|
{
|
|
struct siginfo info;
|
|
memset(&info, 0, sizeof(info));
|
|
info.si_signo = SIGSYS;
|
|
info.si_code = SYS_SECCOMP;
|
|
info.si_call_addr = (void __user *)KSTK_EIP(current);
|
|
info.si_errno = reason;
|
|
info.si_arch = syscall_get_arch();
|
|
info.si_syscall = syscall;
|
|
force_sig_info(SIGSYS, &info, current);
|
|
}
|
|
#endif /* CONFIG_SECCOMP_FILTER */
|
|
|
|
/*
|
|
* Secure computing mode 1 allows only read/write/exit/sigreturn.
|
|
* To be fully secure this must be combined with rlimit
|
|
* to limit the stack allocations too.
|
|
*/
|
|
static int mode1_syscalls[] = {
|
|
__NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
|
|
0, /* null terminated */
|
|
};
|
|
|
|
#ifdef CONFIG_COMPAT
|
|
static int mode1_syscalls_32[] = {
|
|
__NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
|
|
0, /* null terminated */
|
|
};
|
|
#endif
|
|
|
|
int __secure_computing(int this_syscall)
|
|
{
|
|
int mode = current->seccomp.mode;
|
|
int exit_sig = 0;
|
|
int *syscall;
|
|
u32 ret;
|
|
|
|
switch (mode) {
|
|
case SECCOMP_MODE_STRICT:
|
|
syscall = mode1_syscalls;
|
|
#ifdef CONFIG_COMPAT
|
|
if (is_compat_task())
|
|
syscall = mode1_syscalls_32;
|
|
#endif
|
|
do {
|
|
if (*syscall == this_syscall)
|
|
return 0;
|
|
} while (*++syscall);
|
|
exit_sig = SIGKILL;
|
|
ret = SECCOMP_RET_KILL;
|
|
break;
|
|
#ifdef CONFIG_SECCOMP_FILTER
|
|
case SECCOMP_MODE_FILTER: {
|
|
int data;
|
|
struct pt_regs *regs = task_pt_regs(current);
|
|
ret = seccomp_run_filters(this_syscall);
|
|
data = ret & SECCOMP_RET_DATA;
|
|
ret &= SECCOMP_RET_ACTION;
|
|
switch (ret) {
|
|
case SECCOMP_RET_ERRNO:
|
|
/* Set the low-order 16-bits as a errno. */
|
|
syscall_set_return_value(current, regs,
|
|
-data, 0);
|
|
goto skip;
|
|
case SECCOMP_RET_TRAP:
|
|
/* Show the handler the original registers. */
|
|
syscall_rollback(current, regs);
|
|
/* Let the filter pass back 16 bits of data. */
|
|
seccomp_send_sigsys(this_syscall, data);
|
|
goto skip;
|
|
case SECCOMP_RET_TRACE:
|
|
/* Skip these calls if there is no tracer. */
|
|
if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
|
|
syscall_set_return_value(current, regs,
|
|
-ENOSYS, 0);
|
|
goto skip;
|
|
}
|
|
/* Allow the BPF to provide the event message */
|
|
ptrace_event(PTRACE_EVENT_SECCOMP, data);
|
|
/*
|
|
* The delivery of a fatal signal during event
|
|
* notification may silently skip tracer notification.
|
|
* Terminating the task now avoids executing a system
|
|
* call that may not be intended.
|
|
*/
|
|
if (fatal_signal_pending(current))
|
|
break;
|
|
if (syscall_get_nr(current, regs) < 0)
|
|
goto skip; /* Explicit request to skip. */
|
|
|
|
return 0;
|
|
case SECCOMP_RET_ALLOW:
|
|
return 0;
|
|
case SECCOMP_RET_KILL:
|
|
default:
|
|
break;
|
|
}
|
|
exit_sig = SIGSYS;
|
|
break;
|
|
}
|
|
#endif
|
|
default:
|
|
BUG();
|
|
}
|
|
|
|
#ifdef SECCOMP_DEBUG
|
|
dump_stack();
|
|
#endif
|
|
audit_seccomp(this_syscall, exit_sig, ret);
|
|
do_exit(exit_sig);
|
|
#ifdef CONFIG_SECCOMP_FILTER
|
|
skip:
|
|
audit_seccomp(this_syscall, exit_sig, ret);
|
|
#endif
|
|
return -1;
|
|
}
|
|
|
|
long prctl_get_seccomp(void)
|
|
{
|
|
return current->seccomp.mode;
|
|
}
|
|
|
|
/**
|
|
* prctl_set_seccomp: configures current->seccomp.mode
|
|
* @seccomp_mode: requested mode to use
|
|
* @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
|
|
*
|
|
* This function may be called repeatedly with a @seccomp_mode of
|
|
* SECCOMP_MODE_FILTER to install additional filters. Every filter
|
|
* successfully installed will be evaluated (in reverse order) for each system
|
|
* call the task makes.
|
|
*
|
|
* Once current->seccomp.mode is non-zero, it may not be changed.
|
|
*
|
|
* Returns 0 on success or -EINVAL on failure.
|
|
*/
|
|
long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
|
|
{
|
|
long ret = -EINVAL;
|
|
|
|
if (current->seccomp.mode &&
|
|
current->seccomp.mode != seccomp_mode)
|
|
goto out;
|
|
|
|
switch (seccomp_mode) {
|
|
case SECCOMP_MODE_STRICT:
|
|
ret = 0;
|
|
#ifdef TIF_NOTSC
|
|
disable_TSC();
|
|
#endif
|
|
break;
|
|
#ifdef CONFIG_SECCOMP_FILTER
|
|
case SECCOMP_MODE_FILTER:
|
|
ret = seccomp_attach_user_filter(filter);
|
|
if (ret)
|
|
goto out;
|
|
break;
|
|
#endif
|
|
default:
|
|
goto out;
|
|
}
|
|
|
|
current->seccomp.mode = seccomp_mode;
|
|
set_thread_flag(TIF_SECCOMP);
|
|
out:
|
|
return ret;
|
|
}
|