From: Eric W. Biederman ebiederm@xmission.com
commit 7d613f9f72ec8f90ddefcae038fdae5adb8404b3 upstream.
The existence of sigkill_pending is a little silly as it is functionally a duplicate of fatal_signal_pending that is used in exactly one place.
Checking for pending fatal signals and returning early in ptrace_stop is actively harmful. It casues the ptrace_stop called by ptrace_signal to return early before setting current->exit_code. Later when ptrace_signal reads the signal number from current->exit_code is undefined, making it unpredictable what will happen.
Instead rely on the fact that schedule will not sleep if there is a pending signal that can awaken a task.
Removing the explict sigkill_pending test fixes fixes ptrace_signal when ptrace_stop does not stop because current->exit_code is always set to to signr.
Cc: stable@vger.kernel.org Fixes: 3d749b9e676b ("ptrace: simplify ptrace_stop()->sigkill_pending() path") Fixes: 1a669c2f16d4 ("Add arch_ptrace_stop") Link: https://lkml.kernel.org/r/87pmsyx29t.fsf@disp2133 Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/signal.c | 17 ++--------------- 1 file changed, 2 insertions(+), 15 deletions(-)
--- a/kernel/signal.c +++ b/kernel/signal.c @@ -1824,16 +1824,6 @@ static inline int may_ptrace_stop(void) }
/* - * Return non-zero if there is a SIGKILL that should be waking us up. - * Called with the siglock held. - */ -static int sigkill_pending(struct task_struct *tsk) -{ - return sigismember(&tsk->pending.signal, SIGKILL) || - sigismember(&tsk->signal->shared_pending.signal, SIGKILL); -} - -/* * This must be called with current->sighand->siglock held. * * This should be the path for all ptrace stops. @@ -1858,15 +1848,10 @@ static void ptrace_stop(int exit_code, i * calling arch_ptrace_stop, so we must release it now. * To preserve proper semantics, we must do this before * any signal bookkeeping like checking group_stop_count. - * Meanwhile, a SIGKILL could come in before we retake the - * siglock. That must prevent us from sleeping in TASK_TRACED. - * So after regaining the lock, we must check for SIGKILL. */ spin_unlock_irq(¤t->sighand->siglock); arch_ptrace_stop(exit_code, info); spin_lock_irq(¤t->sighand->siglock); - if (sigkill_pending(current)) - return; }
/* @@ -1875,6 +1860,8 @@ static void ptrace_stop(int exit_code, i * Also, transition to TRACED and updates to ->jobctl should be * atomic with respect to siglock and should be done after the arch * hook as siglock is released and regrabbed across it. + * schedule() will not sleep if there is a pending signal that + * can awaken the task. */ set_current_state(TASK_TRACED);