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authorLinus Torvalds <torvalds@linux-foundation.org>2010-02-07 10:11:23 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-02-07 10:26:01 -0800
commit80e1e823989ec44d8e35bdfddadbddcffec90424 (patch)
treead6fd35a0130bc47b082135724834f7db5548c12 /fs
parent29275254caedfedce960cfe6df24b90cb04fe431 (diff)
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Fix race in tty_fasync() properly
This reverts commit 703625118069 ("tty: fix race in tty_fasync") and commit b04da8bfdfbb ("fnctl: f_modown should call write_lock_irqsave/ restore") that tried to fix up some of the fallout but was incomplete. It turns out that we really cannot hold 'tty->ctrl_lock' over calling __f_setown, because not only did that cause problems with interrupt disables (which the second commit fixed), it also causes a potential ABBA deadlock due to lock ordering. Thanks to Tetsuo Handa for following up on the issue, and running lockdep to show the problem. It goes roughly like this: - f_getown gets filp->f_owner.lock for reading without interrupts disabled, so an interrupt that happens while that lock is held can cause a lockdep chain from f_owner.lock -> sighand->siglock. - at the same time, the tty->ctrl_lock -> f_owner.lock chain that commit 703625118069 introduced, together with the pre-existing sighand->siglock -> tty->ctrl_lock chain means that we have a lock dependency the other way too. So instead of extending tty->ctrl_lock over the whole __f_setown() call, we now just take a reference to the 'pid' structure while holding the lock, and then release it after having done the __f_setown. That still guarantees that 'struct pid' won't go away from under us, which is all we really ever needed. Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Acked-by: Greg Kroah-Hartman <gregkh@suse.de> Acked-by: Américo Wang <xiyou.wangcong@gmail.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/fcntl.c6
1 files changed, 2 insertions, 4 deletions
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 5ef953e6f90..97e01dc0d95 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -199,9 +199,7 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
int force)
{
- unsigned long flags;
-
- write_lock_irqsave(&filp->f_owner.lock, flags);
+ write_lock_irq(&filp->f_owner.lock);
if (force || !filp->f_owner.pid) {
put_pid(filp->f_owner.pid);
filp->f_owner.pid = get_pid(pid);
@@ -213,7 +211,7 @@ static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
filp->f_owner.euid = cred->euid;
}
}
- write_unlock_irqrestore(&filp->f_owner.lock, flags);
+ write_unlock_irq(&filp->f_owner.lock);
}
int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,