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authorbsegall@google.com <bsegall@google.com>2017-04-07 16:04:51 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-04-08 00:47:48 -0700
commit5402e97af667e35e54177af8f6575518bf251d51 (patch)
treeab4ca3429a677d0e91c237713891406e5628e90a /kernel/ptrace.c
parentd79bf21e0e02f8ad24219f0587cc599a7e67f6c6 (diff)
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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. Oleg said: "The kernel can crash or this can lead to other hard-to-debug problems. In short, "task->state = TASK_TRACED" in ptrace_unfreeze_traced() assumes that nobody else can wake it up, but PTRACE_LISTEN breaks the contract. Obviusly it is very wrong to manipulate task->state if this task is already running, or WAKING, or it sleeps again" [akpm@linux-foundation.org: coding-style fixes] Fixes: 9899d11f ("ptrace: ensure arch_ptrace/ptrace_request can never race with SIGKILL") Link: http://lkml.kernel.org/r/xm26y3vfhmkp.fsf_-_@bsegall-linux.mtv.corp.google.com Signed-off-by: Ben Segall <bsegall@google.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/ptrace.c')
-rw-r--r--kernel/ptrace.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 0af928712174..266ddcc1d8bb 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -184,11 +184,17 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
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);
}