[PATCH] file: Add locking to f_getown

This has been needed for a long time, but now with the advent of a
reference counted struct pid there are real consequences for getting this
wrong.

Someone I think it was Oleg Nesterov pointed out that this construct was
missing locking, when I introduced struct pid.  After taking time to review
the locking construct already present I figured out which lock needs to be
taken.  The other paths that access f_owner.pid take either the f_owner
read or the write lock.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/fcntl.c b/fs/fcntl.c
index e7c66a1..e4f2616 100644 (file)
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -305,9 +305,11 @@ void f_delown(struct file *filp)
 pid_t f_getown(struct file *filp)
 {
        pid_t pid;
+       read_lock(&filp->f_owner.lock);
        pid = pid_nr(filp->f_owner.pid);
        if (filp->f_owner.pid_type == PIDTYPE_PGID)
                pid = -pid;
+       read_unlock(&filp->f_owner.lock);
        return pid;
 }