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authorBoqun Feng <boqun.feng@gmail.com>2020-11-05 14:23:51 +0800
committerJeff Layton <jlayton@kernel.org>2020-11-05 07:44:15 -0500
commit8d1ddb5e79374fb277985a6b3faa2ed8631c5b4c (patch)
tree9697ee00b6b700bb9977e51a75d6793c49fb1013 /fs/fcntl.c
parent529adfe8f131c60938ece113379f1a07640aefb1 (diff)
downloadlwn-8d1ddb5e79374fb277985a6b3faa2ed8631c5b4c.tar.gz
lwn-8d1ddb5e79374fb277985a6b3faa2ed8631c5b4c.zip
fcntl: Fix potential deadlock in send_sig{io, urg}()
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>
Diffstat (limited to 'fs/fcntl.c')
-rw-r--r--fs/fcntl.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 19ac5baad50f..05b36b28f2e8 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -781,9 +781,10 @@ 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;
@@ -804,7 +805,7 @@ 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,
@@ -819,9 +820,10 @@ 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;
@@ -844,7 +846,7 @@ 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;
}