[PATCH AUTOSEL 5.14 38/47] fcntl: fix potential deadlocks for &fown_struct.lock

[PATCH AUTOSEL 5.14 38/47] fcntl: fix potential deadlocks for &fown_struct.lock

[Sasha Levin]

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

[PATCH AUTOSEL 5.14 39/47] fcntl: fix potential deadlock for &fasync_struct.fa_lock

[Sasha Levin]

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

[ Upstream commit 2f488f698fda820f8e6fa0407630154eceb145d6 ]

There is an existing lock hierarchy of
&dev->event_lock --> &fasync_struct.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,...);

&dev->event_lock is HARDIRQ-safe, so interrupts have to be disabled
while grabbing &fasync_struct.fa_lock, otherwise we invert the lock
hierarchy. However, since kill_fasync which calls kill_fasync_rcu is
an exported symbol, it may not necessarily be called with interrupts
disabled.

As kill_fasync_rcu may be called with interrupts disabled (for
example, in the call chain above), we replace calls to
read_lock/read_unlock on &fasync_struct.fa_lock in kill_fasync_rcu
with read_lock_irqsave/read_unlock_irqrestore.

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 | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 932ec1e9f5bf..68added37c15 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -1004,13 +1004,14 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)
 {
 	while (fa) {
 		struct fown_struct *fown;
+		unsigned long flags;
 
 		if (fa->magic != FASYNC_MAGIC) {
 			printk(KERN_ERR "kill_fasync: bad magic number in "
 			       "fasync_struct!\n");
 			return;
 		}
-		read_lock(&fa->fa_lock);
+		read_lock_irqsave(&fa->fa_lock, flags);
 		if (fa->fa_file) {
 			fown = &fa->fa_file->f_owner;
 			/* Don't send SIGURG to processes which have not set a
@@ -1019,7 +1020,7 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)
 			if (!(sig == SIGURG && fown->signum == 0))
 				send_sigio(fown, fa->fa_fd, band);
 		}
-		read_unlock(&fa->fa_lock);
+		read_unlock_irqrestore(&fa->fa_lock, flags);
 		fa = rcu_dereference(fa->fa_next);
 	}
 }
-- 
2.30.2