[PATCH 5.14 038/334] fcntl: fix potential deadlocks for &fown_struct.lock

Greg Kroah-Hartman
2021-09-13T14:24:13Z

From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>

[ Upstream commit f671a691e299f58835d4660d642582bf0e8f6fda ]

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.

Reported-and-tested-by: syzbot+e6d5398a02c516ce5e70@syzkaller.appspotmail.com
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/fcntl.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index f946bec8f1f1..932ec1e9f5bf 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]);
--
2.30.2