From: Oleg Nesterov Date: Fri, 8 Feb 2008 12:19:18 +0000 (-0800) Subject: uglify kill_pid_info() to fix kill() vs exec() race X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=d36174bc2bce0372693a9cfbdef8b2689c9982cb;p=deliverable%2Flinux.git 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 Cc: "Eric W. Biederman" Cc: Davide Libenzi Cc: Pavel Emelyanov Cc: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/signal.c b/kernel/signal.c index 3d3adb94561d..b0b43a4ad8dd 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -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 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);