The patch titled
Subject: ptrace: fix PTRACE_LISTEN race corrupting task->state
has been added to the -mm tree. Its filename is
ptrace-fix-ptrace_listen-race-corrupting-task-state.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ptrace-fix-ptrace_listen-race-corrupting-task-state.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ptrace-fix-ptrace_listen-race-corrupting-task-state.patch
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------------------------------------------------------
From: bsegall@xxxxxxxxxx
Subject: ptrace: fix PTRACE_LISTEN race corrupting task->state
In PT_SEIZED + LISTEN mode STOP/CONT signals cause a wakeup against
__TASK_TRACED. If this races with the ptrace_unfreeze_traced at the end
of a PTRACE_LISTEN, this can wake the task /after/ the check against
__TASK_TRACED, but before the reset of state to TASK_TRACED. This causes
it to instead clobber TASK_WAKING, allowing a subsequent wakeup against
TRACED while the task is still on the rq wake_list, corrupting it.
Link: http://lkml.kernel.org/r/xm26y3vfhmkp.fsf_-_@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ben Segall <bsegall@xxxxxxxxxx>
---
v2: slight clarification in comments, put the conditional around the
whole wakeup area
Oleg mentioned a preference for making LISTEN unfreeze instead; I have
no preference there, just wanted to make sure that this doesn't get
forgotten entirely.
1 file changed, 10 insertions(+), 4 deletions(-)
index 0af928712174..7cc49c3e73af 100644
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/ptrace.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff -puN kernel/ptrace.c~ptrace-fix-ptrace_listen-race-corrupting-task-state kernel/ptrace.c
--- a/kernel/ptrace.c~ptrace-fix-ptrace_listen-race-corrupting-task-state
+++ a/kernel/ptrace.c
@@ -184,11 +184,17 @@ static void ptrace_unfreeze_traced(struc
WARN_ON(!task->ptrace || task->parent != current);
+ /*
+ * PTRACE_LISTEN can allow ptrace_trap_notify to wake us up
+ * remotely. Recheck state under the lock to close this race.
+ */
spin_lock_irq(&task->sighand->siglock);
- if (__fatal_signal_pending(task))
- wake_up_state(task, __TASK_TRACED);
- else
- task->state = TASK_TRACED;
+ if (task->state == __TASK_TRACED) {
+ if (__fatal_signal_pending(task))
+ wake_up_state(task, __TASK_TRACED);
+ else
+ task->state = TASK_TRACED;
+ }
spin_unlock_irq(&task->sighand->siglock);
}
_
Patches currently in -mm which might be from bsegall@xxxxxxxxxx are
ptrace-fix-ptrace_listen-race-corrupting-task-state.patch
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