linux-kernel - Re: [PATCH] inotify: inotify_destroy_mark

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Message-Id: <1245324318.13761.23295.camel@twins>
Date:	Thu, 18 Jun 2009 13:25:18 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk
Subject: Re: [PATCH] inotify: inotify_destroy_mark_entry could get called
 twice

On Fri, 2009-06-12 at 16:26 -0400, Eric Paris wrote:
> inotify_destroy_mark_entry could get called twice for the same mark since it
> is called directly in inotify_rm_watch and when the mark is being destroyed for
> another reason.  As an example assume that the file being watched was just
> deleted so inotify_destroy_mark_entry would get called from the path
> fsnotify_inoderemove() -> fsnotify_destroy_marks_by_inode() ->
> fsnotify_destroy_mark_entry() -> inotify_destroy_mark_entry().  If this
> happened at the same time as userspace tried to remove a watch via
> inotify_rm_watch we could attempt to remove the mark from the idr twice and
> could thus double dec the ref cnt and potentially could be in a use after
> free/double free situation.  The fix is to have inotify_rm_watch use the
> generic recursive safe fsnotify_destroy_mark_by_entry() so we are sure the
> inotify_destroy_mark_entry() function can only be called one.
> 
> This patch also renames the function to inotify_ingored_remove_idr() so it is
> clear what is actually going on in the function.
> 
> Hopefully this fixes:
> [   20.342058] idr_remove called for id=20 which is not allocated.
> [   20.348000] Pid: 1860, comm: udevd Not tainted 2.6.30-tip #1077
> [   20.353933] Call Trace:
> [   20.356410]  [<ffffffff811a82b7>] idr_remove+0x115/0x18f
> [   20.361737]  [<ffffffff8134259d>] ? _spin_lock+0x6d/0x75
> [   20.367061]  [<ffffffff8111640a>] ? inotify_destroy_mark_entry+0xa3/0xcf
> [   20.373771]  [<ffffffff8111641e>] inotify_destroy_mark_entry+0xb7/0xcf
> [   20.380306]  [<ffffffff81115913>] inotify_freeing_mark+0xe/0x10
> [   20.386238]  [<ffffffff8111410d>] fsnotify_destroy_mark_by_entry+0x143/0x170
> [   20.393293]  [<ffffffff811163a3>] inotify_destroy_mark_entry+0x3c/0xcf
> [   20.399829]  [<ffffffff811164d1>] sys_inotify_rm_watch+0x9b/0xc6
> [   20.405850]  [<ffffffff8100bcdb>] system_call_fastpath+0x16/0x1b
> 
> Reported-by: Peter Zijlstra <peterz@...radead.org>

Tested-by: Peter Zijlstra <peterz@...radead.org>

Thanks Eric!!

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