The patch titled
ptrace_stop: fix racy nonstop_code setting
has been added to the -mm tree. Its filename is
ptrace_stop-fix-racy-nonstop_code-setting.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: ptrace_stop: fix racy nonstop_code setting
From: Oleg Nesterov <oleg@xxxxxxxxxx>
If the tracer is gone and we are not going to stop, ptrace_stop() sets
->exit_code = nostop_code. However, the tracer could actually clear the
exit code before detaching. In that case get_signal_to_deliver() "resends"
the signal which was cancelled by the debugger. For example, it is
possible that a quick PTRACE_ATTACH + PTRACE_DETACH can leave the tracee in
STOPPED state.
Change the behaviour of ptrace_stop(). If the caller is ptrace notify(),
we should always clear ->exit_code. If the caller is
get_signal_to_deliver(), we should not touch it at all. To do so, change
the nonstop_code parameter to "bool clear_code" and change the callers
accordingly.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/signal.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff -puN kernel/signal.c~ptrace_stop-fix-racy-nonstop_code-setting kernel/signal.c
--- a/kernel/signal.c~ptrace_stop-fix-racy-nonstop_code-setting
+++ a/kernel/signal.c
@@ -1601,10 +1601,10 @@ static inline int may_ptrace_stop(void)
* That makes it a way to test a stopped process for
* being ptrace-stopped vs being job-control-stopped.
*
- * If we actually decide not to stop at all because the tracer is gone,
- * we leave nostop_code in current->exit_code.
+ * If we actually decide not to stop at all because the tracer
+ * is gone, we keep current->exit_code unless clear_code.
*/
-static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
+static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
{
/*
* If there is a group stop in progress,
@@ -1631,7 +1631,8 @@ static void ptrace_stop(int exit_code, i
* Don't drop the lock yet, another tracer may come.
*/
__set_current_state(TASK_RUNNING);
- current->exit_code = nostop_code;
+ if (clear_code)
+ current->exit_code = 0;
read_unlock(&tasklist_lock);
}
@@ -1665,7 +1666,7 @@ void ptrace_notify(int exit_code)
/* Let the debugger run. */
spin_lock_irq(¤t->sighand->siglock);
- ptrace_stop(exit_code, 0, &info);
+ ptrace_stop(exit_code, 1, &info);
spin_unlock_irq(¤t->sighand->siglock);
}
@@ -1813,7 +1814,7 @@ relock:
ptrace_signal_deliver(regs, cookie);
/* Let the debugger run. */
- ptrace_stop(signr, signr, info);
+ ptrace_stop(signr, 0, info);
/* We're back. Did the debugger cancel the sig? */
signr = current->exit_code;
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
wait_task_stopped-dont-use-task_pid_nr_ns-lockless.patch
proc-remove-races-from-proc_id_readdir.patch
wait_task_stopped-pass-correct-exit_code-to.patch
use-__set_task_state-for-traced-stopped-tasks.patch
add-task_wakekill.patch
do_wait-remove-one-else-if-branch.patch
proc-implement-proc_single_file_operations.patch
proc-rewrite-do_task_stat-to-correctly-handle-pid-namespaces.patch
proc-seqfile-convert-proc_pid_statm.patch
proc-proper-pidns-handling-for-proc-self.patch
proc-fix-the-threaded-proc-self.patch
kill-pt_attached.patch
kill-my_ptrace_child.patch
ptrace_check_attach-remove-unneeded-signal-=-null-check.patch
ptrace_stop-fix-the-race-with-ptrace-detachattach.patch
wait_task_stopped-simplify-and-fix-races-with-sigcont-sigkill-untrace.patch
do_wait-factor-out-retval-=-0-checks.patch
ptrace_stop-fix-racy-nonstop_code-setting.patch
-
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