uglify kill_pid_info() to fix kill() vs exec() race
kill_pid_info()->pid_task() could be the old leader of the execing process.
In that case it is possible that the leader will be released before we take
siglock. This means that kill_pid_info() (and thus sys_kill()) can return a
false -ESRCH.
Change the code to retry when lock_task_sighand() fails. The endless loop is
not possible, __exit_signal() both clears ->sighand and does detach_pid().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/signal.c b/kernel/signal.c
index 3d3adb9..b0b43a4 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1050,17 +1050,26 @@
int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)
{
- int error;
+ int error = -ESRCH;
struct task_struct *p;
rcu_read_lock();
if (unlikely(sig_needs_tasklist(sig)))
read_lock(&tasklist_lock);
+retry:
p = pid_task(pid, PIDTYPE_PID);
- error = -ESRCH;
- if (p)
+ if (p) {
error = group_send_sig_info(sig, info, p);
+ if (unlikely(error == -ESRCH))
+ /*
+ * The task was unhashed in between, try again.
+ * If it is dead, pid_task() will return NULL,
+ * if we race with de_thread() it will find the
+ * new leader.
+ */
+ goto retry;
+ }
if (unlikely(sig_needs_tasklist(sig)))
read_unlock(&tasklist_lock);