From: Al Viro <viro@zeniv.linux.org.uk>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Jens Axboe <axboe@kernel.dk>,
syzbot <syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
syzkaller-bugs@googlegroups.com, io-uring@vger.kernel.org
Subject: Re: [syzbot] WARNING in mntput_no_expire (2)
Date: Mon, 5 Apr 2021 18:28:54 +0000 [thread overview]
Message-ID: <YGtW5g6EFFArtevk@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <YGtVtfbYXck3qPRl@zeniv-ca.linux.org.uk>
On Mon, Apr 05, 2021 at 06:23:49PM +0000, Al Viro wrote:
> On Mon, Apr 05, 2021 at 07:08:01PM +0200, Christian Brauner wrote:
>
> > Ah dentry count of -127 looks... odd.
>
> dead + 1...
>
> void lockref_mark_dead(struct lockref *lockref)
> {
> assert_spin_locked(&lockref->lock);
> lockref->count = -128;
> }
>
> IOW, a leaked (uncounted) reference to dentry, that got dget() called on
> it after dentry had been freed.
>
> IOW, current->fs->pwd.dentry happens to point to an already freed
> struct dentry here. Joy...
>
> Could you slap
>
> spin_lock(¤t->fs->lock);
> WARN_ON(d_count(current->fs->pwd.dentry) < 0);
> spin_unlock(¤t->fs->lock);
>
> before and after calls of io_issue_sqe() and see if it triggers? We definitely
> are seeing buggered dentry refcounting here.
Check if this helps, please.
diff --git a/fs/namei.c b/fs/namei.c
index 216f16e74351..82344f1139ff 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2289,6 +2289,9 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
int error;
const char *s = nd->name->name;
+ nd->path.mnt = NULL;
+ nd->path.dentry = NULL;
+
/* LOOKUP_CACHED requires RCU, ask caller to retry */
if ((flags & (LOOKUP_RCU | LOOKUP_CACHED)) == LOOKUP_CACHED)
return ERR_PTR(-EAGAIN);
@@ -2322,8 +2325,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
}
nd->root.mnt = NULL;
- nd->path.mnt = NULL;
- nd->path.dentry = NULL;
/* Absolute pathname -- fetch the root (LOOKUP_IN_ROOT uses nd->dfd). */
if (*s == '/' && !(flags & LOOKUP_IN_ROOT)) {
next prev parent reply other threads:[~2021-04-05 18:29 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 9:09 [syzbot] WARNING in mntput_no_expire (2) syzbot
2021-04-01 12:16 ` syzbot
2021-04-01 18:32 ` Christian Brauner
2021-04-01 15:45 ` Christian Brauner
2021-04-01 16:09 ` Jens Axboe
2021-04-01 17:46 ` Christian Brauner
2021-04-01 17:59 ` Christian Brauner
2021-04-01 19:11 ` Al Viro
2021-04-04 2:34 ` Al Viro
2021-04-04 2:38 ` Al Viro
2021-04-04 11:34 ` Christian Brauner
2021-04-04 15:56 ` Al Viro
2021-04-04 16:40 ` Christian Brauner
2021-04-04 16:44 ` Al Viro
2021-04-04 17:05 ` Christian Brauner
2021-04-04 18:50 ` Al Viro
2021-04-04 20:17 ` Al Viro
2021-04-05 11:44 ` Christian Brauner
2021-04-05 16:18 ` Al Viro
2021-04-05 17:08 ` Christian Brauner
2021-04-05 18:23 ` Al Viro
2021-04-05 18:28 ` Al Viro [this message]
2021-04-05 20:07 ` Christian Brauner
2021-04-06 1:38 ` Al Viro
2021-04-06 2:24 ` Al Viro
2021-04-06 12:35 ` Christian Brauner
2021-04-06 13:13 ` Al Viro
2021-04-06 13:22 ` Christian Brauner
2021-04-06 14:15 ` Al Viro
2021-04-06 14:23 ` Al Viro
2021-04-06 15:37 ` Jens Axboe
2021-04-06 14:46 ` Christian Brauner
2021-04-04 16:52 ` Christian Brauner
2021-04-04 16:55 ` Christian Brauner
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