linux-kernel - [PATCH 1/2] uglify kill_pid_info() to fix kill() vs exec() race

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <20071207170333.GA13829@tv-sign.ru>
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/