[PATCH AUTOSEL 5.4 014/130] fcntl: Fix potential deadlock in send_sig{io, urg}()

Sasha Levin
2020-12-23T03:05:21Z

From: Boqun Feng <boqun.feng@gmail.com>

[ Upstream commit 8d1ddb5e79374fb277985a6b3faa2ed8631c5b4c ]

Syzbot reports a potential deadlock found by the newly added recursive
read deadlock detection in lockdep:

[...] ========================================================
[...] WARNING: possible irq lock inversion dependency detected
[...] 5.9.0-rc2-syzkaller #0 Not tainted
[...] --------------------------------------------------------
[...] syz-executor.1/10214 just changed the state of lock:
[...] ffff88811f506338 (&f->f_owner.lock){.+..}-{2:2}, at: send_sigurg+0x1d/0x200
[...] 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 ***

The corresponding deadlock case is as followed:

CPU 0 CPU 1 CPU 2
read_lock(&fown->lock);
spin_lock_irqsave(&dev->event_lock, ...)
write_lock_irq(&filp->f_owner.lock); // wait for the lock
read_lock(&fown-lock); // have to wait until the writer release
// due to the fairness
<interrupted>
spin_lock_irqsave(&dev->event_lock); // wait for the lock

The lock dependency on CPU 1 happens if there exists a call sequence:

input_inject_event():
spin_lock_irqsave(&dev->event_lock,...);
input_handle_event():
input_pass_values():
input_to_handler():
handler->event(): // evdev_event()
evdev_pass_values():
spin_lock(&client->buffer_lock);
__pass_event():
kill_fasync():
kill_fasync_rcu():
read_lock(&fa->fa_lock);
send_sigio():
read_lock(&fown->lock);

To fix this, make the reader in send_sigurg() and send_sigio() use
read_lock_irqsave() and read_lock_irqrestore().

Reported-by: syzbot+22e87cdf94021b984aa6@syzkaller.appspotmail.com
Reported-by: syzbot+c5e32344981ad9f33750@syzkaller.appspotmail.com
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/fcntl.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 3d40771e8e7cf..3dc90e5293e65 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -779,9 +779,10 @@ void send_sigio(struct fown_struct *fown, int fd, int band)
{
struct task_struct *p;
enum pid_type type;
+ unsigned long flags;
struct pid *pid;

- read_lock(&fown->lock);
+ read_lock_irqsave(&fown->lock, flags);

type = fown->pid_type;
pid = fown->pid;
@@ -802,7 +803,7 @@ void send_sigio(struct fown_struct *fown, int fd, int band)
read_unlock(&tasklist_lock);
}
out_unlock_fown:
- read_unlock(&fown->lock);
+ read_unlock_irqrestore(&fown->lock, flags);
}

static void send_sigurg_to_task(struct task_struct *p,
@@ -817,9 +818,10 @@ int send_sigurg(struct fown_struct *fown)
struct task_struct *p;
enum pid_type type;
struct pid *pid;
+ unsigned long flags;
int ret = 0;

- read_lock(&fown->lock);
+ read_lock_irqsave(&fown->lock, flags);

type = fown->pid_type;
pid = fown->pid;
@@ -842,7 +844,7 @@ int send_sigurg(struct fown_struct *fown)
read_unlock(&tasklist_lock);
}
out_unlock_fown:
- read_unlock(&fown->lock);
+ read_unlock_irqrestore(&fown->lock, flags);
return ret;
}

--
2.27.0