On Fri, 2021-07-02 at 17:18 +0800, Desmond Cheong Zhi Xi wrote:
> Syzbot reports a potential deadlock in do_fcntl:
>
> ========================================================
> WARNING: possible irq lock inversion dependency detected
> 5.12.0-syzkaller #0 Not tainted
> --------------------------------------------------------
> syz-executor132/8391 just changed the state of lock:
> ffff888015967bf8 (&f->f_owner.lock){.+..}-{2:2}, at: f_getown_ex fs/fcntl.c:211 [inline]
> ffff888015967bf8 (&f->f_owner.lock){.+..}-{2:2}, at: do_fcntl+0x8b4/0x1200 fs/fcntl.c:395
> but this lock was taken by another, HARDIRQ-safe lock in the past:
> (&dev->event_lock){-...}-{2:2}
>
> and interrupts could create inverse lock ordering between them.
>
> other info that might help us debug this:
> Chain exists of:
> &dev->event_lock --> &new->fa_lock --> &f->f_owner.lock
>
> Possible interrupt unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&f->f_owner.lock);
> local_irq_disable();
> lock(&dev->event_lock);
> lock(&new->fa_lock);
> <Interrupt>
> lock(&dev->event_lock);
>
> *** DEADLOCK ***
>
> This happens because there is a lock hierarchy of
> &dev->event_lock --> &new->fa_lock --> &f->f_owner.lock
> from the following call chain:
>
> input_inject_event():
> spin_lock_irqsave(&dev->event_lock,...);
> input_handle_event():
> input_pass_values():
> input_to_handler():
> evdev_events():
> evdev_pass_values():
> spin_lock(&client->buffer_lock);
> __pass_event():
> kill_fasync():
> kill_fasync_rcu():
> read_lock(&fa->fa_lock);
> send_sigio():
> read_lock_irqsave(&fown->lock,...);
>
> However, since &dev->event_lock is HARDIRQ-safe, interrupts have to be
> disabled while grabbing &f->f_owner.lock, otherwise we invert the lock
> hierarchy.
>
> Hence, we replace calls to read_lock/read_unlock on &f->f_owner.lock,
> with read_lock_irq/read_unlock_irq.
>
Patches look reasonable overall, but why does this one use read_lock_irq
and the other one use read_lock_irqsave? Don't we need to *_irqsasve in
both patches?
> Reported-and-tested-by: syzbot+e6d5398a02c516ce5e70@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
> ---
> fs/fcntl.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index dfc72f15be7f..cf9e81dfa615 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -150,7 +150,8 @@ void f_delown(struct file *filp)
> pid_t f_getown(struct file *filp)
> {
> pid_t pid = 0;
> - read_lock(&filp->f_owner.lock);
> +
> + read_lock_irq(&filp->f_owner.lock);
> rcu_read_lock();
> if (pid_task(filp->f_owner.pid, filp->f_owner.pid_type)) {
> pid = pid_vnr(filp->f_owner.pid);
> @@ -158,7 +159,7 @@ pid_t f_getown(struct file *filp)
> pid = -pid;
> }
> rcu_read_unlock();
> - read_unlock(&filp->f_owner.lock);
> + read_unlock_irq(&filp->f_owner.lock);
> return pid;
> }
>
> @@ -208,7 +209,7 @@ static int f_getown_ex(struct file *filp, unsigned long arg)
> struct f_owner_ex owner = {};
> int ret = 0;
>
> - read_lock(&filp->f_owner.lock);
> + read_lock_irq(&filp->f_owner.lock);
> rcu_read_lock();
> if (pid_task(filp->f_owner.pid, filp->f_owner.pid_type))
> owner.pid = pid_vnr(filp->f_owner.pid);
> @@ -231,7 +232,7 @@ static int f_getown_ex(struct file *filp, unsigned long arg)
> ret = -EINVAL;
> break;
> }
> - read_unlock(&filp->f_owner.lock);
> + read_unlock_irq(&filp->f_owner.lock);
>
> if (!ret) {
> ret = copy_to_user(owner_p, &owner, sizeof(owner));
> @@ -249,10 +250,10 @@ static int f_getowner_uids(struct file *filp, unsigned long arg)
> uid_t src[2];
> int err;
>
> - read_lock(&filp->f_owner.lock);
> + read_lock_irq(&filp->f_owner.lock);
> src[0] = from_kuid(user_ns, filp->f_owner.uid);
> src[1] = from_kuid(user_ns, filp->f_owner.euid);
> - read_unlock(&filp->f_owner.lock);
> + read_unlock_irq(&filp->f_owner.lock);
>
> err = put_user(src[0], &dst[0]);
> err |= put_user(src[1], &dst[1]);
--
Jeff Layton <jlayton@xxxxxxxxxx>
