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![Linus Torvalds](/assets/img/avatar_default.png)
This reverts commits4bad58ebc8
(and399f8dd9a8
, which tried to fix it). I do not believe these are correct, and I'm about to release 5.13, so am reverting them out of an abundance of caution. The locking is odd, and appears broken. On the allocation side (in __sigqueue_alloc()), the locking is somewhat straightforward: it depends on sighand->siglock. Since one caller doesn't hold that lock, it further then tests 'sigqueue_flags' to avoid the case with no locks held. On the freeing side (in sigqueue_cache_or_free()), there is no locking at all, and the logic instead depends on 'current' being a single thread, and not able to race with itself. To make things more exciting, there's also the data race between freeing a signal and allocating one, which is handled by using WRITE_ONCE() and READ_ONCE(), and being mutually exclusive wrt the initial state (ie freeing will only free if the old state was NULL, while allocating will obviously only use the value if it was non-NULL, so only one or the other will actually act on the value). However, while the free->alloc paths do seem mutually exclusive thanks to just the data value dependency, it's not clear what the memory ordering constraints are on it. Could writes from the previous allocation possibly be delayed and seen by the new allocation later, causing logical inconsistencies? So it's all very exciting and unusual. And in particular, it seems that the freeing side is incorrect in depending on "current" being single-threaded. Yes, 'current' is a single thread, but in the presense of asynchronous events even a single thread can have data races. And such asynchronous events can and do happen, with interrupts causing signals to be flushed and thus free'd (for example - sending a SIGCONT/SIGSTOP can happen from interrupt context, and can flush previously queued process control signals). So regardless of all the other questions about the memory ordering and locking for this new cached allocation, the sigqueue_cache_or_free() assumptions seem to be fundamentally incorrect. It may be that people will show me the errors of my ways, and tell me why this is all safe after all. We can reinstate it if so. But my current belief is that the WRITE_ONCE() that sets the cached entry needs to be a smp_store_release(), and the READ_ONCE() that finds a cached entry needs to be a smp_load_acquire() to handle memory ordering correctly. And the sequence in sigqueue_cache_or_free() would need to either use a lock or at least be interrupt-safe some way (perhaps by using something like the percpu 'cmpxchg': it doesn't need to be SMP-safe, but like the percpu operations it needs to be interrupt-safe). Fixes:399f8dd9a8
("signal: Prevent sigqueue caching after task got released") Fixes:4bad58ebc8
("signal: Allow tasks to cache one sigqueue struct") Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
488 lines
14 KiB
C
488 lines
14 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_SIGNAL_H
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#define _LINUX_SIGNAL_H
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#include <linux/bug.h>
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#include <linux/signal_types.h>
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#include <linux/string.h>
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struct task_struct;
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/* for sysctl */
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extern int print_fatal_signals;
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static inline void copy_siginfo(kernel_siginfo_t *to,
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const kernel_siginfo_t *from)
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{
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memcpy(to, from, sizeof(*to));
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}
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static inline void clear_siginfo(kernel_siginfo_t *info)
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{
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memset(info, 0, sizeof(*info));
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}
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#define SI_EXPANSION_SIZE (sizeof(struct siginfo) - sizeof(struct kernel_siginfo))
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static inline void copy_siginfo_to_external(siginfo_t *to,
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const kernel_siginfo_t *from)
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{
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memcpy(to, from, sizeof(*from));
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memset(((char *)to) + sizeof(struct kernel_siginfo), 0,
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SI_EXPANSION_SIZE);
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}
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int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from);
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int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from);
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enum siginfo_layout {
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SIL_KILL,
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SIL_TIMER,
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SIL_POLL,
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SIL_FAULT,
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SIL_FAULT_TRAPNO,
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SIL_FAULT_MCEERR,
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SIL_FAULT_BNDERR,
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SIL_FAULT_PKUERR,
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SIL_PERF_EVENT,
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SIL_CHLD,
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SIL_RT,
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SIL_SYS,
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};
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enum siginfo_layout siginfo_layout(unsigned sig, int si_code);
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/*
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* Define some primitives to manipulate sigset_t.
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*/
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#ifndef __HAVE_ARCH_SIG_BITOPS
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#include <linux/bitops.h>
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/* We don't use <linux/bitops.h> for these because there is no need to
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be atomic. */
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static inline void sigaddset(sigset_t *set, int _sig)
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{
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unsigned long sig = _sig - 1;
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if (_NSIG_WORDS == 1)
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set->sig[0] |= 1UL << sig;
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else
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set->sig[sig / _NSIG_BPW] |= 1UL << (sig % _NSIG_BPW);
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}
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static inline void sigdelset(sigset_t *set, int _sig)
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{
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unsigned long sig = _sig - 1;
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if (_NSIG_WORDS == 1)
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set->sig[0] &= ~(1UL << sig);
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else
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set->sig[sig / _NSIG_BPW] &= ~(1UL << (sig % _NSIG_BPW));
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}
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static inline int sigismember(sigset_t *set, int _sig)
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{
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unsigned long sig = _sig - 1;
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if (_NSIG_WORDS == 1)
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return 1 & (set->sig[0] >> sig);
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else
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return 1 & (set->sig[sig / _NSIG_BPW] >> (sig % _NSIG_BPW));
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}
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#endif /* __HAVE_ARCH_SIG_BITOPS */
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static inline int sigisemptyset(sigset_t *set)
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{
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switch (_NSIG_WORDS) {
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case 4:
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return (set->sig[3] | set->sig[2] |
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set->sig[1] | set->sig[0]) == 0;
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case 2:
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return (set->sig[1] | set->sig[0]) == 0;
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case 1:
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return set->sig[0] == 0;
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default:
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BUILD_BUG();
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return 0;
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}
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}
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static inline int sigequalsets(const sigset_t *set1, const sigset_t *set2)
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{
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switch (_NSIG_WORDS) {
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case 4:
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return (set1->sig[3] == set2->sig[3]) &&
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(set1->sig[2] == set2->sig[2]) &&
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(set1->sig[1] == set2->sig[1]) &&
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(set1->sig[0] == set2->sig[0]);
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case 2:
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return (set1->sig[1] == set2->sig[1]) &&
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(set1->sig[0] == set2->sig[0]);
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case 1:
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return set1->sig[0] == set2->sig[0];
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}
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return 0;
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}
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#define sigmask(sig) (1UL << ((sig) - 1))
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#ifndef __HAVE_ARCH_SIG_SETOPS
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#include <linux/string.h>
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#define _SIG_SET_BINOP(name, op) \
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static inline void name(sigset_t *r, const sigset_t *a, const sigset_t *b) \
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{ \
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unsigned long a0, a1, a2, a3, b0, b1, b2, b3; \
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\
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switch (_NSIG_WORDS) { \
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case 4: \
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a3 = a->sig[3]; a2 = a->sig[2]; \
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b3 = b->sig[3]; b2 = b->sig[2]; \
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r->sig[3] = op(a3, b3); \
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r->sig[2] = op(a2, b2); \
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fallthrough; \
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case 2: \
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a1 = a->sig[1]; b1 = b->sig[1]; \
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r->sig[1] = op(a1, b1); \
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fallthrough; \
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case 1: \
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a0 = a->sig[0]; b0 = b->sig[0]; \
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r->sig[0] = op(a0, b0); \
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break; \
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default: \
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BUILD_BUG(); \
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} \
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}
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#define _sig_or(x,y) ((x) | (y))
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_SIG_SET_BINOP(sigorsets, _sig_or)
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#define _sig_and(x,y) ((x) & (y))
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_SIG_SET_BINOP(sigandsets, _sig_and)
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#define _sig_andn(x,y) ((x) & ~(y))
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_SIG_SET_BINOP(sigandnsets, _sig_andn)
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#undef _SIG_SET_BINOP
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#undef _sig_or
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#undef _sig_and
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#undef _sig_andn
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#define _SIG_SET_OP(name, op) \
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static inline void name(sigset_t *set) \
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{ \
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switch (_NSIG_WORDS) { \
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case 4: set->sig[3] = op(set->sig[3]); \
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set->sig[2] = op(set->sig[2]); \
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fallthrough; \
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case 2: set->sig[1] = op(set->sig[1]); \
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fallthrough; \
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case 1: set->sig[0] = op(set->sig[0]); \
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break; \
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default: \
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BUILD_BUG(); \
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} \
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}
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#define _sig_not(x) (~(x))
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_SIG_SET_OP(signotset, _sig_not)
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#undef _SIG_SET_OP
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#undef _sig_not
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static inline void sigemptyset(sigset_t *set)
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{
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switch (_NSIG_WORDS) {
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default:
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memset(set, 0, sizeof(sigset_t));
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break;
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case 2: set->sig[1] = 0;
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fallthrough;
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case 1: set->sig[0] = 0;
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break;
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}
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}
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static inline void sigfillset(sigset_t *set)
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{
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switch (_NSIG_WORDS) {
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default:
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memset(set, -1, sizeof(sigset_t));
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break;
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case 2: set->sig[1] = -1;
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fallthrough;
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case 1: set->sig[0] = -1;
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break;
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}
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}
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/* Some extensions for manipulating the low 32 signals in particular. */
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static inline void sigaddsetmask(sigset_t *set, unsigned long mask)
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{
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set->sig[0] |= mask;
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}
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static inline void sigdelsetmask(sigset_t *set, unsigned long mask)
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{
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set->sig[0] &= ~mask;
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}
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static inline int sigtestsetmask(sigset_t *set, unsigned long mask)
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{
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return (set->sig[0] & mask) != 0;
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}
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static inline void siginitset(sigset_t *set, unsigned long mask)
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{
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set->sig[0] = mask;
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switch (_NSIG_WORDS) {
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default:
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memset(&set->sig[1], 0, sizeof(long)*(_NSIG_WORDS-1));
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break;
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case 2: set->sig[1] = 0;
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break;
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case 1: ;
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}
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}
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static inline void siginitsetinv(sigset_t *set, unsigned long mask)
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{
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set->sig[0] = ~mask;
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switch (_NSIG_WORDS) {
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default:
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memset(&set->sig[1], -1, sizeof(long)*(_NSIG_WORDS-1));
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break;
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case 2: set->sig[1] = -1;
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break;
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case 1: ;
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}
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}
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#endif /* __HAVE_ARCH_SIG_SETOPS */
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static inline void init_sigpending(struct sigpending *sig)
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{
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sigemptyset(&sig->signal);
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INIT_LIST_HEAD(&sig->list);
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}
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extern void flush_sigqueue(struct sigpending *queue);
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/* Test if 'sig' is valid signal. Use this instead of testing _NSIG directly */
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static inline int valid_signal(unsigned long sig)
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{
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return sig <= _NSIG ? 1 : 0;
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}
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struct timespec;
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struct pt_regs;
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enum pid_type;
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extern int next_signal(struct sigpending *pending, sigset_t *mask);
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extern int do_send_sig_info(int sig, struct kernel_siginfo *info,
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struct task_struct *p, enum pid_type type);
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extern int group_send_sig_info(int sig, struct kernel_siginfo *info,
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struct task_struct *p, enum pid_type type);
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extern int __group_send_sig_info(int, struct kernel_siginfo *, struct task_struct *);
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extern int sigprocmask(int, sigset_t *, sigset_t *);
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extern void set_current_blocked(sigset_t *);
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extern void __set_current_blocked(const sigset_t *);
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extern int show_unhandled_signals;
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extern bool get_signal(struct ksignal *ksig);
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extern void signal_setup_done(int failed, struct ksignal *ksig, int stepping);
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extern void exit_signals(struct task_struct *tsk);
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extern void kernel_sigaction(int, __sighandler_t);
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#define SIG_KTHREAD ((__force __sighandler_t)2)
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#define SIG_KTHREAD_KERNEL ((__force __sighandler_t)3)
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static inline void allow_signal(int sig)
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{
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/*
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* Kernel threads handle their own signals. Let the signal code
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* know it'll be handled, so that they don't get converted to
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* SIGKILL or just silently dropped.
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*/
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kernel_sigaction(sig, SIG_KTHREAD);
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}
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static inline void allow_kernel_signal(int sig)
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{
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/*
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* Kernel threads handle their own signals. Let the signal code
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* know signals sent by the kernel will be handled, so that they
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* don't get silently dropped.
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*/
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kernel_sigaction(sig, SIG_KTHREAD_KERNEL);
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}
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static inline void disallow_signal(int sig)
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{
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kernel_sigaction(sig, SIG_IGN);
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}
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extern struct kmem_cache *sighand_cachep;
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extern bool unhandled_signal(struct task_struct *tsk, int sig);
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/*
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* In POSIX a signal is sent either to a specific thread (Linux task)
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* or to the process as a whole (Linux thread group). How the signal
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* is sent determines whether it's to one thread or the whole group,
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* which determines which signal mask(s) are involved in blocking it
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* from being delivered until later. When the signal is delivered,
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* either it's caught or ignored by a user handler or it has a default
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* effect that applies to the whole thread group (POSIX process).
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*
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* The possible effects an unblocked signal set to SIG_DFL can have are:
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* ignore - Nothing Happens
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* terminate - kill the process, i.e. all threads in the group,
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* similar to exit_group. The group leader (only) reports
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* WIFSIGNALED status to its parent.
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* coredump - write a core dump file describing all threads using
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* the same mm and then kill all those threads
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* stop - stop all the threads in the group, i.e. TASK_STOPPED state
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*
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* SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.
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* Other signals when not blocked and set to SIG_DFL behaves as follows.
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* The job control signals also have other special effects.
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*
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* +--------------------+------------------+
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* | POSIX signal | default action |
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* +--------------------+------------------+
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* | SIGHUP | terminate |
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* | SIGINT | terminate |
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* | SIGQUIT | coredump |
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* | SIGILL | coredump |
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* | SIGTRAP | coredump |
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* | SIGABRT/SIGIOT | coredump |
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* | SIGBUS | coredump |
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* | SIGFPE | coredump |
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* | SIGKILL | terminate(+) |
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* | SIGUSR1 | terminate |
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* | SIGSEGV | coredump |
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* | SIGUSR2 | terminate |
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* | SIGPIPE | terminate |
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* | SIGALRM | terminate |
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* | SIGTERM | terminate |
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* | SIGCHLD | ignore |
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* | SIGCONT | ignore(*) |
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* | SIGSTOP | stop(*)(+) |
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* | SIGTSTP | stop(*) |
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* | SIGTTIN | stop(*) |
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* | SIGTTOU | stop(*) |
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* | SIGURG | ignore |
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* | SIGXCPU | coredump |
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* | SIGXFSZ | coredump |
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* | SIGVTALRM | terminate |
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* | SIGPROF | terminate |
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* | SIGPOLL/SIGIO | terminate |
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* | SIGSYS/SIGUNUSED | coredump |
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* | SIGSTKFLT | terminate |
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* | SIGWINCH | ignore |
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* | SIGPWR | terminate |
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* | SIGRTMIN-SIGRTMAX | terminate |
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* +--------------------+------------------+
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* | non-POSIX signal | default action |
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* +--------------------+------------------+
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* | SIGEMT | coredump |
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* +--------------------+------------------+
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*
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* (+) For SIGKILL and SIGSTOP the action is "always", not just "default".
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* (*) Special job control effects:
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* When SIGCONT is sent, it resumes the process (all threads in the group)
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* from TASK_STOPPED state and also clears any pending/queued stop signals
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* (any of those marked with "stop(*)"). This happens regardless of blocking,
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* catching, or ignoring SIGCONT. When any stop signal is sent, it clears
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* any pending/queued SIGCONT signals; this happens regardless of blocking,
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* catching, or ignored the stop signal, though (except for SIGSTOP) the
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* default action of stopping the process may happen later or never.
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*/
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#ifdef SIGEMT
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#define SIGEMT_MASK rt_sigmask(SIGEMT)
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#else
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#define SIGEMT_MASK 0
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#endif
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#if SIGRTMIN > BITS_PER_LONG
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#define rt_sigmask(sig) (1ULL << ((sig)-1))
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#else
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#define rt_sigmask(sig) sigmask(sig)
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#endif
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#define siginmask(sig, mask) \
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((sig) > 0 && (sig) < SIGRTMIN && (rt_sigmask(sig) & (mask)))
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#define SIG_KERNEL_ONLY_MASK (\
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rt_sigmask(SIGKILL) | rt_sigmask(SIGSTOP))
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#define SIG_KERNEL_STOP_MASK (\
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rt_sigmask(SIGSTOP) | rt_sigmask(SIGTSTP) | \
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rt_sigmask(SIGTTIN) | rt_sigmask(SIGTTOU) )
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#define SIG_KERNEL_COREDUMP_MASK (\
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rt_sigmask(SIGQUIT) | rt_sigmask(SIGILL) | \
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rt_sigmask(SIGTRAP) | rt_sigmask(SIGABRT) | \
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rt_sigmask(SIGFPE) | rt_sigmask(SIGSEGV) | \
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rt_sigmask(SIGBUS) | rt_sigmask(SIGSYS) | \
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rt_sigmask(SIGXCPU) | rt_sigmask(SIGXFSZ) | \
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SIGEMT_MASK )
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#define SIG_KERNEL_IGNORE_MASK (\
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rt_sigmask(SIGCONT) | rt_sigmask(SIGCHLD) | \
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rt_sigmask(SIGWINCH) | rt_sigmask(SIGURG) )
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#define SIG_SPECIFIC_SICODES_MASK (\
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rt_sigmask(SIGILL) | rt_sigmask(SIGFPE) | \
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rt_sigmask(SIGSEGV) | rt_sigmask(SIGBUS) | \
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rt_sigmask(SIGTRAP) | rt_sigmask(SIGCHLD) | \
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rt_sigmask(SIGPOLL) | rt_sigmask(SIGSYS) | \
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SIGEMT_MASK )
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#define sig_kernel_only(sig) siginmask(sig, SIG_KERNEL_ONLY_MASK)
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#define sig_kernel_coredump(sig) siginmask(sig, SIG_KERNEL_COREDUMP_MASK)
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|
#define sig_kernel_ignore(sig) siginmask(sig, SIG_KERNEL_IGNORE_MASK)
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|
#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 unsafe_save_altstack(uss, sp, label) do { \
|
|
stack_t __user *__uss = uss; \
|
|
struct task_struct *t = current; \
|
|
unsafe_put_user((void __user *)t->sas_ss_sp, &__uss->ss_sp, label); \
|
|
unsafe_put_user(t->sas_ss_flags, &__uss->ss_flags, label); \
|
|
unsafe_put_user(t->sas_ss_size, &__uss->ss_size, label); \
|
|
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
|
|
|
|
#ifndef arch_untagged_si_addr
|
|
/*
|
|
* Given a fault address and a signal and si_code which correspond to the
|
|
* _sigfault union member, returns the address that must appear in si_addr if
|
|
* the signal handler does not have SA_EXPOSE_TAGBITS enabled in sa_flags.
|
|
*/
|
|
static inline void __user *arch_untagged_si_addr(void __user *addr,
|
|
unsigned long sig,
|
|
unsigned long si_code)
|
|
{
|
|
return addr;
|
|
}
|
|
#endif
|
|
|
|
#endif /* _LINUX_SIGNAL_H */
|