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Re: [PATCH] xfsprogs: fix Out-of-bounds access in repair/dinode.c

To: Eric Sandeen <sandeen@xxxxxxxxxxx>, Rich Johnston <rjohnston@xxxxxxx>, Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH] xfsprogs: fix Out-of-bounds access in repair/dinode.c
From: Ben Myers <bpm@xxxxxxx>
Date: Mon, 26 Aug 2013 12:40:30 -0500
Cc: Chandra Seetharaman <sekharan@xxxxxxxxxx>, xfsprogs <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <521B8E51.6090405@xxxxxxxxxxx>
References: <1376287861.2822.13.camel@ThinkPad-T5421> <5214EFFF.4060105@xxxxxxx> <20130823163828.GS5262@xxxxxxx> <521B8E51.6090405@xxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Hey,

On Mon, Aug 26, 2013 at 12:20:17PM -0500, Eric Sandeen wrote:
> On 8/23/13 11:38 AM, Ben Myers wrote:
> > Hey Rich and Li Zhong,
> > 
> > On Wed, Aug 21, 2013 at 11:51:11AM -0500, Rich Johnston wrote:
> >> Looks good, thanks for the patch Li Zhong. it has been committed.
> >>
> >> --Rich
> >>
> >> Reviewed-by: Rich Johnston <rjohnston@xxxxxxx>
> >>
> >> commit e7c05095f5baa9cd2e35a6de03d7dd9f51dd3910
> >> Author: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
> >> Date:   Mon Aug 12 06:11:01 2013 +0000
> >>
> >>     xfsprogs: fix Out-of-bounds access in repair/dinode.c
> >>
> >> On 08/12/2013 01:11 AM, Li Zhong wrote:
> >>> Following is reported by coverity in bug 1061528:
> >>>
> >>> 187                        __dirty_no_modify_ret(dirty);
> >>>
> >>> CID 1061528 (#1 of 1): Out-of-bounds access (OVERRUN)53. 
> >>> overrun-buffer-arg: Overrunning array "dinoc->di_pad" of 6 bytes by 
> >>> passing it to a function which accesses it at byte offset 15 using 
> >>> argument "16UL".
> >>> 188                        memset(dinoc->di_pad, 0, 16);
> >>>
> >>> It seems that di_pad here should be di_pad2, as sekharan pointed out.
> >>>
> >>> Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
> >>> ---
> >>>  repair/dinode.c | 4 ++--
> >>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/repair/dinode.c b/repair/dinode.c
> >>> index e607f0b..94bf2f8 100644
> >>> --- a/repair/dinode.c
> >>> +++ b/repair/dinode.c
> >>> @@ -183,9 +183,9 @@ clear_dinode_core(struct xfs_mount *mp, xfs_dinode_t 
> >>> *dinoc, xfs_ino_t ino_num)
> >>>   }
> >>>
> >>>   for (i = 0; i < 16; i++) {
> >>> -         if (dinoc->di_pad[i] != 0) {
> >>> +         if (dinoc->di_pad2[i] != 0) {
> >>>                   __dirty_no_modify_ret(dirty);
> >>> -                 memset(dinoc->di_pad, 0, 16);
> >>> +                 memset(dinoc->di_pad2, 0, 16);
> >>>                   break;
> >>>           }
> >>>   }
> > 
> > We also discussed this issue a bit in this thread:
> > http://oss.sgi.com/archives/xfs/2013-08/msg00228.html
> > 
> > Looks like the loop itself is incorrect and should be removed, and Eric has
> > suggested that the conditional be changed to a memcmp in case the size of 
> > the
> > pad changes in the future.  Would either of you care to spin up another 
> > patch
> > to clean it up?
> 
> I think I was confused; it seems fine as it is in git, not sure what I was
> thinking.
> 
> memcmp can't use a bare "0" as an arg, so it's not ideal to use either.
> 
> Not a huge fan of the hard-coded 16, but I think the code is correct now; we
> can probably move on to real problems.  ;)

185         for (i = 0; i < 16; i++) {
186                 if (dinoc->di_pad2[i] != 0) {
187                         __dirty_no_modify_ret(dirty);
188                         memset(dinoc->di_pad2, 0, 16);
189                         break;
190                 }
191         }

D'oh!  I was mistaken too!
        
I was thinking that line 188 read 'memset(&dinoc->di_pad2[i], 0, 16);' and that
we were going off the end of the array as i increased...  Teach me to look a
little closer.

I agree that the current code is fine.

Apologies to Rich and Zhong.

-Ben

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