[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <20071117181549.GA1415@tv-sign.ru>
Date: Sat, 17 Nov 2007 21:15:49 +0300
From: Oleg Nesterov <oleg@...sign.ru>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
Pavel Emelyanov <xemul@...nvz.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH] task_pid_nr_ns() breaks proc_pid_readdir()
proc_pid_readdir:
for (...; ...; task = next_tgid(tgid + 1, ns)) {
tgid = task_pid_nr_ns(task, ns);
... use tgid ...
The first problem is that task_pid_nr_ns() can race with RCU and read the
freed memory.
However, rcu_read_lock() can't help. next_tgid() returns a pinned task_struct,
but the task can be released (and it's pid detached) before task_pid_nr_ns()
reads the pid_t value. In that case task_pid_nr_ns() returns 0 thus breaking
the whole logic.
Make sure that task_pid_nr_ns() returns !0 before updating tgid. Note that
next_tgid(tgid + 1) can find the same "struct pid" again, but we shouldn't
go into the endless loop because pid_task(PIDTYPE_PID) must return NULL in
this case, so next_tgid() can't return the same task.
Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
--- 24/fs/proc/base.c~pprd 2007-10-25 16:22:11.000000000 +0400
+++ 24/fs/proc/base.c 2007-11-17 20:58:14.000000000 +0300
@@ -2481,7 +2481,15 @@ int proc_pid_readdir(struct file * filp,
for (task = next_tgid(tgid, ns);
task;
put_task_struct(task), task = next_tgid(tgid + 1, ns)) {
- tgid = task_pid_nr_ns(task, ns);
+ int nr;
+
+ rcu_read_lock();
+ nr = task_pid_nr_ns(task, ns);
+ rcu_read_unlock();
+ if (!nr)
+ continue;
+
+ tgid = nr;
filp->f_pos = tgid + TGID_OFFSET;
if (proc_pid_fill_cache(filp, dirent, filldir, task, tgid) < 0) {
put_task_struct(task);
-
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/
Powered by blists - more mailing lists