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uglify kill_pid_info() to fix kill() vs exec() race

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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>
This commit is contained in:
Oleg Nesterov 2008-02-08 04:19:18 -08:00 committed by Linus Torvalds
parent f374ada53b
commit d36174bc2b
1 changed files with 12 additions and 3 deletions
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15
kernel/signal.c
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@ -1050,17 +1050,26 @@ int kill_pgrp_info(int sig, struct siginfo *info, struct pid *pgrp)
int kill_pid_info(int sig, struct siginfo *info, struct pid *pid) int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)
{ {
int error; int error = -ESRCH;
struct task_struct *p; struct task_struct *p;
rcu_read_lock(); rcu_read_lock();
if (unlikely(sig_needs_tasklist(sig))) if (unlikely(sig_needs_tasklist(sig)))
read_lock(&tasklist_lock); read_lock(&tasklist_lock);
retry:
p = pid_task(pid, PIDTYPE_PID); p = pid_task(pid, PIDTYPE_PID);
error = -ESRCH; if (p) {
if (p)
error = group_send_sig_info(sig, info, 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))) if (unlikely(sig_needs_tasklist(sig)))
read_unlock(&tasklist_lock); read_unlock(&tasklist_lock);