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Date: Fri, 7 Dec 2007 20:03:33 +0300 From: Oleg Nesterov <oleg@...sign.ru> To: Andrew Morton <akpm@...ux-foundation.org> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Davide Libenzi <davidel@...ilserver.org>, Pavel Emelyanov <xemul@...nvz.org>, Roland McGrath <roland@...hat.com>, linux-kernel@...r.kernel.org Subject: [PATCH 1/2] 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@...sign.ru> --- PT/kernel/signal.c~1_kill_exec_race 2007-12-06 18:13:31.000000000 +0300 +++ PT/kernel/signal.c 2007-12-07 17:20:27.000000000 +0300 @@ -1049,17 +1049,26 @@ int kill_pgrp_info(int sig, struct sigin 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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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