diff options
author | Eric W. Biederman <ebiederm@xmission.com> | 2021-11-17 19:47:15 +0300 |
---|---|---|
committer | Eric W. Biederman <ebiederm@xmission.com> | 2021-11-17 19:49:51 +0300 |
commit | 5ae9497dda62833a33c4f8817a52d91b4ae1a140 (patch) | |
tree | c617015a169edd12e5ad16ec375afadc2c4004ed | |
parent | fa55b7dcdc43c1aa1ba12bca9d2dd4318c2a0dbf (diff) | |
parent | b171f667f3787946a8ba9644305339e93ae799c9 (diff) | |
download | linux-5ae9497dda62833a33c4f8817a52d91b4ae1a140.tar.xz |
signal: requeuing undeliverable signals
Kyle Huey recently reported[1] that rr gets confused if SIGKILL prevents
ptrace_signal from delivering a signal, as the kernel setups up a signal
frame for a signal that rr did not have a chance to observe with ptrace.
In looking into it I found a couple of bugs and a quality of
implementation issue.
- The test for signal_group_exit should be inside the for loop in get_signal.
- Signals should be requeued on the same queue they were dequeued from.
- When a fatal signal is pending ptrace_signal should not return another
signal for delivery.
Kyle Huey has verified[2] an earlier version of this change.
I have reworked things one more time to completely fix the issues
raised, and to keep the code maintainable long term.
I have smoke tested this code and combined with a careful review I
expect this code to work fine. Kyle if you can double check that
my last round of changes still works for rr I would appreciate it.
Eric W. Biederman (3):
signal: In get_signal test for signal_group_exit every time through the loop
signal: Requeue signals in the appropriate queue
signal: Requeue ptrace signals
fs/signalfd.c | 5 +++--
include/linux/sched/signal.h | 7 ++++---
kernel/signal.c | 44 ++++++++++++++++++++++++++------------------
3 files changed, 33 insertions(+), 23 deletions(-)
[1] https://lkml.kernel.org/r/20211101034147.6203-1-khuey@kylehuey.com
[2] https://lkml.kernel.org/r/CAP045ApAX725ZfujaK-jJNkfCo5s+oVFpBvNfPJk+DKY8K7d=Q@mail.gmail.com
Tested-by: Kyle Huey <khuey@kylehuey.com>
Link: https://lkml.kernel.org/r/87bl2kekig.fsf_-_@email.froward.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
-rw-r--r-- | fs/signalfd.c | 5 | ||||
-rw-r--r-- | include/linux/sched/signal.h | 7 | ||||
-rw-r--r-- | kernel/signal.c | 44 |
3 files changed, 33 insertions, 23 deletions
diff --git a/fs/signalfd.c b/fs/signalfd.c index 040e1cf90528..74f134cd1ff6 100644 --- a/fs/signalfd.c +++ b/fs/signalfd.c @@ -165,11 +165,12 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo, static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info, int nonblock) { + enum pid_type type; ssize_t ret; DECLARE_WAITQUEUE(wait, current); spin_lock_irq(¤t->sighand->siglock); - ret = dequeue_signal(current, &ctx->sigmask, info); + ret = dequeue_signal(current, &ctx->sigmask, info, &type); switch (ret) { case 0: if (!nonblock) @@ -184,7 +185,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info add_wait_queue(¤t->sighand->signalfd_wqh, &wait); for (;;) { set_current_state(TASK_INTERRUPTIBLE); - ret = dequeue_signal(current, &ctx->sigmask, info); + ret = dequeue_signal(current, &ctx->sigmask, info, &type); if (ret != 0) break; if (signal_pending(current)) { diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 23505394ef70..167995d471da 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -286,17 +286,18 @@ static inline int signal_group_exit(const struct signal_struct *sig) extern void flush_signals(struct task_struct *); extern void ignore_signals(struct task_struct *); extern void flush_signal_handlers(struct task_struct *, int force_default); -extern int dequeue_signal(struct task_struct *task, - sigset_t *mask, kernel_siginfo_t *info); +extern int dequeue_signal(struct task_struct *task, sigset_t *mask, + kernel_siginfo_t *info, enum pid_type *type); static inline int kernel_dequeue_signal(void) { struct task_struct *task = current; kernel_siginfo_t __info; + enum pid_type __type; int ret; spin_lock_irq(&task->sighand->siglock); - ret = dequeue_signal(task, &task->blocked, &__info); + ret = dequeue_signal(task, &task->blocked, &__info, &__type); spin_unlock_irq(&task->sighand->siglock); return ret; diff --git a/kernel/signal.c b/kernel/signal.c index 7c4b7ae714d4..621401550f0f 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -626,7 +626,8 @@ static int __dequeue_signal(struct sigpending *pending, sigset_t *mask, * * All callers have to hold the siglock. */ -int dequeue_signal(struct task_struct *tsk, sigset_t *mask, kernel_siginfo_t *info) +int dequeue_signal(struct task_struct *tsk, sigset_t *mask, + kernel_siginfo_t *info, enum pid_type *type) { bool resched_timer = false; int signr; @@ -634,8 +635,10 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, kernel_siginfo_t *in /* We only dequeue private signals from ourselves, we don't let * signalfd steal them */ + *type = PIDTYPE_PID; signr = __dequeue_signal(&tsk->pending, mask, info, &resched_timer); if (!signr) { + *type = PIDTYPE_TGID; signr = __dequeue_signal(&tsk->signal->shared_pending, mask, info, &resched_timer); #ifdef CONFIG_POSIX_TIMERS @@ -2522,7 +2525,7 @@ static void do_freezer_trap(void) freezable_schedule(); } -static int ptrace_signal(int signr, kernel_siginfo_t *info) +static int ptrace_signal(int signr, kernel_siginfo_t *info, enum pid_type type) { /* * We do not check sig_kernel_stop(signr) but set this marker @@ -2562,8 +2565,9 @@ static int ptrace_signal(int signr, kernel_siginfo_t *info) } /* If the (new) signal is now blocked, requeue it. */ - if (sigismember(¤t->blocked, signr)) { - send_signal(signr, info, current, PIDTYPE_PID); + if (sigismember(¤t->blocked, signr) || + fatal_signal_pending(current)) { + send_signal(signr, info, current, type); signr = 0; } @@ -2662,18 +2666,19 @@ relock: goto relock; } - /* Has this task already been marked for death? */ - if (signal_group_exit(signal)) { - ksig->info.si_signo = signr = SIGKILL; - sigdelset(¤t->pending.signal, SIGKILL); - trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO, - &sighand->action[SIGKILL - 1]); - recalc_sigpending(); - goto fatal; - } - for (;;) { struct k_sigaction *ka; + enum pid_type type; + + /* Has this task already been marked for death? */ + if (signal_group_exit(signal)) { + ksig->info.si_signo = signr = SIGKILL; + sigdelset(¤t->pending.signal, SIGKILL); + trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO, + &sighand->action[SIGKILL - 1]); + recalc_sigpending(); + goto fatal; + } if (unlikely(current->jobctl & JOBCTL_STOP_PENDING) && do_signal_stop(0)) @@ -2706,16 +2711,18 @@ relock: * so that the instruction pointer in the signal stack * frame points to the faulting instruction. */ + type = PIDTYPE_PID; signr = dequeue_synchronous_signal(&ksig->info); if (!signr) - signr = dequeue_signal(current, ¤t->blocked, &ksig->info); + signr = dequeue_signal(current, ¤t->blocked, + &ksig->info, &type); if (!signr) break; /* will return 0 */ if (unlikely(current->ptrace) && (signr != SIGKILL) && !(sighand->action[signr -1].sa.sa_flags & SA_IMMUTABLE)) { - signr = ptrace_signal(signr, &ksig->info); + signr = ptrace_signal(signr, &ksig->info, type); if (!signr) continue; } @@ -3540,6 +3547,7 @@ static int do_sigtimedwait(const sigset_t *which, kernel_siginfo_t *info, ktime_t *to = NULL, timeout = KTIME_MAX; struct task_struct *tsk = current; sigset_t mask = *which; + enum pid_type type; int sig, ret = 0; if (ts) { @@ -3556,7 +3564,7 @@ static int do_sigtimedwait(const sigset_t *which, kernel_siginfo_t *info, signotset(&mask); spin_lock_irq(&tsk->sighand->siglock); - sig = dequeue_signal(tsk, &mask, info); + sig = dequeue_signal(tsk, &mask, info, &type); if (!sig && timeout) { /* * None ready, temporarily unblock those we're interested @@ -3575,7 +3583,7 @@ static int do_sigtimedwait(const sigset_t *which, kernel_siginfo_t *info, spin_lock_irq(&tsk->sighand->siglock); __set_task_blocked(tsk, &tsk->real_blocked); sigemptyset(&tsk->real_blocked); - sig = dequeue_signal(tsk, &mask, info); + sig = dequeue_signal(tsk, &mask, info, &type); } spin_unlock_irq(&tsk->sighand->siglock); |