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alistair23-linux/include/linux/signal.h
Eric W. Biederman 33da8e7c81 signal: Allow cifs and drbd to receive their terminating signals 
My recent to change to only use force_sig for a synchronous events
wound up breaking signal reception cifs and drbd.  I had overlooked
the fact that by default kthreads start out with all signals set to
SIG_IGN.  So a change I thought was safe turned out to have made it
impossible for those kernel thread to catch their signals.

Reverting the work on force_sig is a bad idea because what the code
was doing was very much a misuse of force_sig.  As the way force_sig
ultimately allowed the signal to happen was to change the signal
handler to SIG_DFL.  Which after the first signal will allow userspace
to send signals to these kernel threads.  At least for
wake_ack_receiver in drbd that does not appear actively wrong.

So correct this problem by adding allow_kernel_signal that will allow
signals whose siginfo reports they were sent by the kernel through,
but will not allow userspace generated signals, and update cifs and
drbd to call allow_kernel_signal in an appropriate place so that their
thread can receive this signal.

Fixing things this way ensures that userspace won't be able to send
signals and cause problems, that it is clear which signals the
threads are expecting to receive, and it guarantees that nothing
else in the system will be affected.

This change was partly inspired by similar cifs and drbd patches that
added allow_signal.

Reported-by: ronnie sahlberg <ronniesahlberg@gmail.com>
Reported-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Tested-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Cc: Steve French <smfrench@gmail.com>
Cc: Philipp Reisner <philipp.reisner@linbit.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Fixes: 247bc9470b ("cifs: fix rmmod regression in cifs.ko caused by force_sig changes")
Fixes: 72abe3bcf0 ("signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force_sig")
Fixes: fee109901f ("signal/drbd: Use send_sig not force_sig")
Fixes: 3cf5d076fb ("signal: Remove task parameter from force_sig")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2019-08-19 06:34:13 -05:00

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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_SIGNAL_H
#define _LINUX_SIGNAL_H
#include <linux/bug.h>
#include <linux/signal_types.h>
#include <linux/string.h>
struct task_struct;
/* for sysctl */
extern int print_fatal_signals;
static inline void copy_siginfo(kernel_siginfo_t *to,
const kernel_siginfo_t *from)
{
memcpy(to, from, sizeof(*to));
}
static inline void clear_siginfo(kernel_siginfo_t *info)
{
memset(info, 0, sizeof(*info));
}
#define SI_EXPANSION_SIZE (sizeof(struct siginfo) - sizeof(struct kernel_siginfo))
int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from);
int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from);
enum siginfo_layout {
SIL_KILL,
SIL_TIMER,
SIL_POLL,
SIL_FAULT,
SIL_FAULT_MCEERR,
SIL_FAULT_BNDERR,
SIL_FAULT_PKUERR,
SIL_CHLD,
SIL_RT,
SIL_SYS,
};
enum siginfo_layout siginfo_layout(unsigned sig, int si_code);
/*
* Define some primitives to manipulate sigset_t.
*/
#ifndef __HAVE_ARCH_SIG_BITOPS
#include <linux/bitops.h>
/* We don't use <linux/bitops.h> for these because there is no need to
be atomic. */
static inline void sigaddset(sigset_t *set, int _sig)
{
unsigned long sig = _sig - 1;
if (_NSIG_WORDS == 1)
set->sig[0] |= 1UL << sig;
else
set->sig[sig / _NSIG_BPW] |= 1UL << (sig % _NSIG_BPW);
}
static inline void sigdelset(sigset_t *set, int _sig)
{
unsigned long sig = _sig - 1;
if (_NSIG_WORDS == 1)
set->sig[0] &= ~(1UL << sig);
else
set->sig[sig / _NSIG_BPW] &= ~(1UL << (sig % _NSIG_BPW));
}
static inline int sigismember(sigset_t *set, int _sig)
{
unsigned long sig = _sig - 1;
if (_NSIG_WORDS == 1)
return 1 & (set->sig[0] >> sig);
else
return 1 & (set->sig[sig / _NSIG_BPW] >> (sig % _NSIG_BPW));
}
#endif /* __HAVE_ARCH_SIG_BITOPS */
static inline int sigisemptyset(sigset_t *set)
{
switch (_NSIG_WORDS) {
case 4:
return (set->sig[3] | set->sig[2] |
set->sig[1] | set->sig[0]) == 0;
case 2:
return (set->sig[1] | set->sig[0]) == 0;
case 1:
return set->sig[0] == 0;
default:
BUILD_BUG();
return 0;
}
}
static inline int sigequalsets(const sigset_t *set1, const sigset_t *set2)
{
switch (_NSIG_WORDS) {
case 4:
return (set1->sig[3] == set2->sig[3]) &&
(set1->sig[2] == set2->sig[2]) &&
(set1->sig[1] == set2->sig[1]) &&
(set1->sig[0] == set2->sig[0]);
case 2:
return (set1->sig[1] == set2->sig[1]) &&
(set1->sig[0] == set2->sig[0]);
case 1:
return set1->sig[0] == set2->sig[0];
}
return 0;
}
#define sigmask(sig) (1UL << ((sig) - 1))
#ifndef __HAVE_ARCH_SIG_SETOPS
#include <linux/string.h>
#define _SIG_SET_BINOP(name, op) \
static inline void name(sigset_t *r, const sigset_t *a, const sigset_t *b) \
{ \
unsigned long a0, a1, a2, a3, b0, b1, b2, b3; \
\
switch (_NSIG_WORDS) { \
case 4: \
a3 = a->sig[3]; a2 = a->sig[2]; \
b3 = b->sig[3]; b2 = b->sig[2]; \
r->sig[3] = op(a3, b3); \
r->sig[2] = op(a2, b2); \
/* fall through */ \
case 2: \
a1 = a->sig[1]; b1 = b->sig[1]; \
r->sig[1] = op(a1, b1); \
/* fall through */ \
case 1: \
a0 = a->sig[0]; b0 = b->sig[0]; \
r->sig[0] = op(a0, b0); \
break; \
default: \
BUILD_BUG(); \
} \
}
#define _sig_or(x,y) ((x) | (y))
_SIG_SET_BINOP(sigorsets, _sig_or)
#define _sig_and(x,y) ((x) & (y))
_SIG_SET_BINOP(sigandsets, _sig_and)
#define _sig_andn(x,y) ((x) & ~(y))
_SIG_SET_BINOP(sigandnsets, _sig_andn)
#undef _SIG_SET_BINOP
#undef _sig_or
#undef _sig_and
#undef _sig_andn
#define _SIG_SET_OP(name, op) \
static inline void name(sigset_t *set) \
{ \
switch (_NSIG_WORDS) { \
case 4: set->sig[3] = op(set->sig[3]); \
set->sig[2] = op(set->sig[2]); \
/* fall through */ \
case 2: set->sig[1] = op(set->sig[1]); \
/* fall through */ \
case 1: set->sig[0] = op(set->sig[0]); \
break; \
default: \
BUILD_BUG(); \
} \
}
#define _sig_not(x) (~(x))
_SIG_SET_OP(signotset, _sig_not)
#undef _SIG_SET_OP
#undef _sig_not
static inline void sigemptyset(sigset_t *set)
{
switch (_NSIG_WORDS) {
default:
memset(set, 0, sizeof(sigset_t));
break;
case 2: set->sig[1] = 0;
/* fall through */
case 1: set->sig[0] = 0;
break;
}
}
static inline void sigfillset(sigset_t *set)
{
switch (_NSIG_WORDS) {
default:
memset(set, -1, sizeof(sigset_t));
break;
case 2: set->sig[1] = -1;
/* fall through */
case 1: set->sig[0] = -1;
break;
}
}
/* Some extensions for manipulating the low 32 signals in particular. */
static inline void sigaddsetmask(sigset_t *set, unsigned long mask)
{
set->sig[0] |= mask;
}
static inline void sigdelsetmask(sigset_t *set, unsigned long mask)
{
set->sig[0] &= ~mask;
}
static inline int sigtestsetmask(sigset_t *set, unsigned long mask)
{
return (set->sig[0] & mask) != 0;
}
static inline void siginitset(sigset_t *set, unsigned long mask)
{
set->sig[0] = mask;
switch (_NSIG_WORDS) {
default:
memset(&set->sig[1], 0, sizeof(long)*(_NSIG_WORDS-1));
break;
case 2: set->sig[1] = 0;
case 1: ;
}
}
static inline void siginitsetinv(sigset_t *set, unsigned long mask)
{
set->sig[0] = ~mask;
switch (_NSIG_WORDS) {
default:
memset(&set->sig[1], -1, sizeof(long)*(_NSIG_WORDS-1));
break;
case 2: set->sig[1] = -1;
case 1: ;
}
}
#endif /* __HAVE_ARCH_SIG_SETOPS */
static inline void init_sigpending(struct sigpending *sig)
{
sigemptyset(&sig->signal);
INIT_LIST_HEAD(&sig->list);
}
extern void flush_sigqueue(struct sigpending *queue);
/* Test if 'sig' is valid signal. Use this instead of testing _NSIG directly */
static inline int valid_signal(unsigned long sig)
{
return sig <= _NSIG ? 1 : 0;
}
struct timespec;
struct pt_regs;
enum pid_type;
extern int next_signal(struct sigpending *pending, sigset_t *mask);
extern int do_send_sig_info(int sig, struct kernel_siginfo *info,
struct task_struct *p, enum pid_type type);
extern int group_send_sig_info(int sig, struct kernel_siginfo *info,
struct task_struct *p, enum pid_type type);
extern int __group_send_sig_info(int, struct kernel_siginfo *, struct task_struct *);
extern int sigprocmask(int, sigset_t *, sigset_t *);
extern void set_current_blocked(sigset_t *);
extern void __set_current_blocked(const sigset_t *);
extern int show_unhandled_signals;
extern bool get_signal(struct ksignal *ksig);
extern void signal_setup_done(int failed, struct ksignal *ksig, int stepping);
extern void exit_signals(struct task_struct *tsk);
extern void kernel_sigaction(int, __sighandler_t);
#define SIG_KTHREAD ((__force __sighandler_t)2)
#define SIG_KTHREAD_KERNEL ((__force __sighandler_t)3)
static inline void allow_signal(int sig)
{
/*
* Kernel threads handle their own signals. Let the signal code
* know it'll be handled, so that they don't get converted to
* SIGKILL or just silently dropped.
*/
kernel_sigaction(sig, SIG_KTHREAD);
}
static inline void allow_kernel_signal(int sig)
{
/*
* Kernel threads handle their own signals. Let the signal code
* know signals sent by the kernel will be handled, so that they
* don't get silently dropped.
*/
kernel_sigaction(sig, SIG_KTHREAD_KERNEL);
}
static inline void disallow_signal(int sig)
{
kernel_sigaction(sig, SIG_IGN);
}
extern struct kmem_cache *sighand_cachep;
extern bool unhandled_signal(struct task_struct *tsk, int sig);
/*
* In POSIX a signal is sent either to a specific thread (Linux task)
* or to the process as a whole (Linux thread group). How the signal
* is sent determines whether it's to one thread or the whole group,
* which determines which signal mask(s) are involved in blocking it
* from being delivered until later. When the signal is delivered,
* either it's caught or ignored by a user handler or it has a default
* effect that applies to the whole thread group (POSIX process).
*
* The possible effects an unblocked signal set to SIG_DFL can have are:
* ignore - Nothing Happens
* terminate - kill the process, i.e. all threads in the group,
* similar to exit_group. The group leader (only) reports
* WIFSIGNALED status to its parent.
* coredump - write a core dump file describing all threads using
* the same mm and then kill all those threads
* stop - stop all the threads in the group, i.e. TASK_STOPPED state
*
* SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.
* Other signals when not blocked and set to SIG_DFL behaves as follows.
* The job control signals also have other special effects.
*
* +--------------------+------------------+
* | POSIX signal | default action |
* +--------------------+------------------+
* | SIGHUP | terminate |
* | SIGINT | terminate |
* | SIGQUIT | coredump |
* | SIGILL | coredump |
* | SIGTRAP | coredump |
* | SIGABRT/SIGIOT | coredump |
* | SIGBUS | coredump |
* | SIGFPE | coredump |
* | SIGKILL | terminate(+) |
* | SIGUSR1 | terminate |
* | SIGSEGV | coredump |
* | SIGUSR2 | terminate |
* | SIGPIPE | terminate |
* | SIGALRM | terminate |
* | SIGTERM | terminate |
* | SIGCHLD | ignore |
* | SIGCONT | ignore(*) |
* | SIGSTOP | stop(*)(+) |
* | SIGTSTP | stop(*) |
* | SIGTTIN | stop(*) |
* | SIGTTOU | stop(*) |
* | SIGURG | ignore |
* | SIGXCPU | coredump |
* | SIGXFSZ | coredump |
* | SIGVTALRM | terminate |
* | SIGPROF | terminate |
* | SIGPOLL/SIGIO | terminate |
* | SIGSYS/SIGUNUSED | coredump |
* | SIGSTKFLT | terminate |
* | SIGWINCH | ignore |
* | SIGPWR | terminate |
* | SIGRTMIN-SIGRTMAX | terminate |
* +--------------------+------------------+
* | non-POSIX signal | default action |
* +--------------------+------------------+
* | SIGEMT | coredump |
* +--------------------+------------------+
*
* (+) For SIGKILL and SIGSTOP the action is "always", not just "default".
* (*) Special job control effects:
* When SIGCONT is sent, it resumes the process (all threads in the group)
* from TASK_STOPPED state and also clears any pending/queued stop signals
* (any of those marked with "stop(*)"). This happens regardless of blocking,
* catching, or ignoring SIGCONT. When any stop signal is sent, it clears
* any pending/queued SIGCONT signals; this happens regardless of blocking,
* catching, or ignored the stop signal, though (except for SIGSTOP) the
* default action of stopping the process may happen later or never.
*/
#ifdef SIGEMT
#define SIGEMT_MASK rt_sigmask(SIGEMT)
#else
#define SIGEMT_MASK 0
#endif
#if SIGRTMIN > BITS_PER_LONG
#define rt_sigmask(sig) (1ULL << ((sig)-1))
#else
#define rt_sigmask(sig) sigmask(sig)
#endif
#define siginmask(sig, mask) \
((sig) > 0 && (sig) < SIGRTMIN && (rt_sigmask(sig) & (mask)))
#define SIG_KERNEL_ONLY_MASK (\
rt_sigmask(SIGKILL) | rt_sigmask(SIGSTOP))
#define SIG_KERNEL_STOP_MASK (\
rt_sigmask(SIGSTOP) | rt_sigmask(SIGTSTP) | \
rt_sigmask(SIGTTIN) | rt_sigmask(SIGTTOU) )
#define SIG_KERNEL_COREDUMP_MASK (\
rt_sigmask(SIGQUIT) | rt_sigmask(SIGILL) | \
rt_sigmask(SIGTRAP) | rt_sigmask(SIGABRT) | \
rt_sigmask(SIGFPE) | rt_sigmask(SIGSEGV) | \
rt_sigmask(SIGBUS) | rt_sigmask(SIGSYS) | \
rt_sigmask(SIGXCPU) | rt_sigmask(SIGXFSZ) | \
SIGEMT_MASK )
#define SIG_KERNEL_IGNORE_MASK (\
rt_sigmask(SIGCONT) | rt_sigmask(SIGCHLD) | \
rt_sigmask(SIGWINCH) | rt_sigmask(SIGURG) )
#define SIG_SPECIFIC_SICODES_MASK (\
rt_sigmask(SIGILL) | rt_sigmask(SIGFPE) | \
rt_sigmask(SIGSEGV) | rt_sigmask(SIGBUS) | \
rt_sigmask(SIGTRAP) | rt_sigmask(SIGCHLD) | \
rt_sigmask(SIGPOLL) | rt_sigmask(SIGSYS) | \
SIGEMT_MASK )
#define sig_kernel_only(sig) siginmask(sig, SIG_KERNEL_ONLY_MASK)
#define sig_kernel_coredump(sig) siginmask(sig, SIG_KERNEL_COREDUMP_MASK)
#define sig_kernel_ignore(sig) siginmask(sig, SIG_KERNEL_IGNORE_MASK)
#define sig_kernel_stop(sig) siginmask(sig, SIG_KERNEL_STOP_MASK)
#define sig_specific_sicodes(sig) siginmask(sig, SIG_SPECIFIC_SICODES_MASK)
#define sig_fatal(t, signr) \
(!siginmask(signr, SIG_KERNEL_IGNORE_MASK|SIG_KERNEL_STOP_MASK) && \
(t)->sighand->action[(signr)-1].sa.sa_handler == SIG_DFL)
void signals_init(void);
int restore_altstack(const stack_t __user *);
int __save_altstack(stack_t __user *, unsigned long);
#define save_altstack_ex(uss, sp) do { \
stack_t __user *__uss = uss; \
struct task_struct *t = current; \
put_user_ex((void __user *)t->sas_ss_sp, &__uss->ss_sp); \
put_user_ex(t->sas_ss_flags, &__uss->ss_flags); \
put_user_ex(t->sas_ss_size, &__uss->ss_size); \
if (t->sas_ss_flags & SS_AUTODISARM) \
sas_ss_reset(t); \
} while (0);
#ifdef CONFIG_PROC_FS
struct seq_file;
extern void render_sigset_t(struct seq_file *, const char *, sigset_t *);
#endif
#endif /* _LINUX_SIGNAL_H */
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