linux-kernel - Re: fs: gpf in simple

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Message-ID: <20140305124536.GA32371@quack.suse.cz>
Date:	Wed, 5 Mar 2014 13:45:36 +0100
From:	Jan Kara <jack@...e.cz>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Jan Kara <jack@...e.cz>, Al Viro <viro@...IV.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: fs: gpf in simple_setattr

On Tue 04-03-14 19:00:32, Sasha Levin wrote:
> On 03/03/2014 04:40 PM, Jan Kara wrote:
> >On Sat 01-03-14 15:05:21, Sasha Levin wrote:
> >>>ping again?
> >>>
> >>>I've been working on it, but don't see an obvious issue.
> >>>
> >>>It does look like an access to invalid memory easily doable from
> >>>userspace, so it should probably get fixed soon...
> >   Hum, can you maybe dump the name in dentry passed to simple_setattr()? Or
> >maybe even the whole path using dentry_path() (but not sure if that will
> >be workable on half-torn-down fs)? Maybe it will give us a hint at which
> >filesystem to look...
> 
> It's just garbage, this is why I'm having a hard time making any progress with
> this bug.
  OK, but that is strange because we hold a reference to the dentry so
noone should free it. So dentry->d_name should be valid... Is the rest of
the dentry also garbage? E.g. does dentry->d_inode still point to the inode
we call __mark_inode_dirty() on? Is dentry->d_sb == dentry->d_inode->i_sb?
Also if the inode isn't completely garbage, we can maybe infer something
from inode->i_op - that should point to some statically allocated
operations struct so we should be able to guess fs type from that.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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