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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	xfs@oss.sgi.com
Subject: Re: inode_permission NULL pointer dereference in 3.13-rc1
Date: Fri, 29 Nov 2013 03:59:39 +0000	[thread overview]
Message-ID: <20131129035939.GT10323@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20131129024121.GS10323@ZenIV.linux.org.uk>

On Fri, Nov 29, 2013 at 02:41:21AM +0000, Al Viro wrote:
> On Thu, Nov 28, 2013 at 06:07:27PM -0800, Linus Torvalds wrote:
> 
> > HOWEVER. It's certainly *not* valid if "current->fs->root/pwd" points
> > to it. So yeah, there must have been an extra dput() somewhere. Or,
> > more likely, I think, we don't get the refcount to some dentry
> > properly any more.
> > 
> > I don't see where, though. You did change where "LOOKUP_RCU" is
> > cleared in unlazy_walk() but you did add that
> > 
> >         nd->path.dentry = NULL;
> > 
> > and that looks like it should be ok. And I don't see what else would care.
> 
> *nod*
> 
> BTW, vfsmount refcount is 12, so we *definitely* nowhere near the
> final mntput(), etc. and mnt->mnt_root itself should also have
> contributed.
> 
> I'm going to try to find out _which_ test buggers the refcount - at
> least that way I'll have something resembling a usable reproducer...

OK, we have a winner.  generic/234 drops refcount of root dentry by about
20 (and yes, I should've started with that one, what with Ted's report).
Run it several times (4 should suffice nicely) and the damn thing triggers
right there.  Uff...  At least that takes under a minute instead of a couple
of hours, which makes debugging that shite much more tolerable...

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WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	xfs@oss.sgi.com
Subject: Re: inode_permission NULL pointer dereference in 3.13-rc1
Date: Fri, 29 Nov 2013 03:59:39 +0000	[thread overview]
Message-ID: <20131129035939.GT10323@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20131129024121.GS10323@ZenIV.linux.org.uk>

On Fri, Nov 29, 2013 at 02:41:21AM +0000, Al Viro wrote:
> On Thu, Nov 28, 2013 at 06:07:27PM -0800, Linus Torvalds wrote:
> 
> > HOWEVER. It's certainly *not* valid if "current->fs->root/pwd" points
> > to it. So yeah, there must have been an extra dput() somewhere. Or,
> > more likely, I think, we don't get the refcount to some dentry
> > properly any more.
> > 
> > I don't see where, though. You did change where "LOOKUP_RCU" is
> > cleared in unlazy_walk() but you did add that
> > 
> >         nd->path.dentry = NULL;
> > 
> > and that looks like it should be ok. And I don't see what else would care.
> 
> *nod*
> 
> BTW, vfsmount refcount is 12, so we *definitely* nowhere near the
> final mntput(), etc. and mnt->mnt_root itself should also have
> contributed.
> 
> I'm going to try to find out _which_ test buggers the refcount - at
> least that way I'll have something resembling a usable reproducer...

OK, we have a winner.  generic/234 drops refcount of root dentry by about
20 (and yes, I should've started with that one, what with Ted's report).
Run it several times (4 should suffice nicely) and the damn thing triggers
right there.  Uff...  At least that takes under a minute instead of a couple
of hours, which makes debugging that shite much more tolerable...

  reply	other threads:[~2013-11-29  3:59 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-11-24 14:04 inode_permission NULL pointer dereference in 3.13-rc1 Christoph Hellwig
2013-11-24 15:27 ` Al Viro
2013-11-25 16:06   ` Christoph Hellwig
2013-11-25 16:06     ` Christoph Hellwig
2013-11-26 13:11     ` Al Viro
2013-11-26 13:11       ` Al Viro
2013-11-26 14:12       ` Christoph Hellwig
2013-11-26 14:12         ` Christoph Hellwig
2013-11-27  6:43         ` Al Viro
2013-11-27  6:43           ` Al Viro
2013-11-27 10:09           ` Christoph Hellwig
2013-11-27 10:09             ` Christoph Hellwig
2013-11-28 16:26             ` Al Viro
2013-11-28 16:26               ` Al Viro
2013-11-28 21:23               ` Al Viro
2013-11-28 22:51                 ` Dave Chinner
2013-11-28 23:44                   ` Al Viro
2013-11-28 23:44                     ` Al Viro
2013-11-29  1:46                     ` Dave Chinner
2013-11-29  2:07                       ` Al Viro
2013-11-29  2:07                         ` Al Viro
2013-11-29  2:17                         ` Linus Torvalds
2013-11-29  2:07                     ` Linus Torvalds
2013-11-29  2:07                       ` Linus Torvalds
2013-11-29  2:41                       ` Al Viro
2013-11-29  2:41                         ` Al Viro
2013-11-29  3:59                         ` Al Viro [this message]
2013-11-29  3:59                           ` Al Viro
2013-11-29  4:06                           ` Al Viro
2013-11-29  4:14                             ` Al Viro
2013-11-29  6:59                               ` Al Viro
2013-11-29  6:59                                 ` Al Viro
2013-11-29 19:44                                 ` Greg KH
2013-11-29 19:44                                   ` Greg KH
2013-11-29 20:17                                   ` Linus Torvalds
2013-11-29 20:17                                     ` Linus Torvalds
2013-11-29 23:55                                     ` Al Viro
2013-11-30  0:18                                       ` Linus Torvalds
2013-11-30 15:09                                 ` [GIT PULL] " Theodore Ts'o
2013-11-30 15:09                                   ` Theodore Ts'o
2013-11-30 15:13                                   ` Theodore Ts'o
2013-11-30 15:13                                     ` Theodore Ts'o
2013-11-27 21:51           ` Dave Chinner
2013-11-27 21:51             ` Dave Chinner
2013-11-28 15:21 ` Theodore Ts'o
2013-11-28 15:21   ` Theodore Ts'o
2013-11-28 15:36   ` Theodore Ts'o
2013-11-28 15:36     ` Theodore Ts'o

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