linux-kernel - Re: [syzbot] [kernfs?] possible deadlock in kernfs_fop

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Date: Sat,  6 Apr 2024 07:00:34 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+9a5b0ced8b1bfb238b56@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernfs?] possible deadlock in kernfs_fop_llseek

On Wed, 03 Apr 2024 11:23:26 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    fe46a7dd189e Merge tag 'sound-6.9-rc1' of git://git.kernel..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15c38139180000

Test Al's idea.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  fe46a7dd189e

--- x/fs/overlayfs/util.c
+++ y/fs/overlayfs/util.c
@@ -639,6 +639,8 @@ static int kernfs_fop_open(struct inode
 	 */
 	if (has_mmap)
 		mutex_init(&of->mutex);
+	else if (file->f_mode & FMODE_WRITE)
+		mutex_init(&of->mutex);
 	else
 		mutex_init(&of->mutex);
 
--