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Re: [PATCH][RFC] XFS: Fix mem leak and possible NULL deref in xfs_setatt

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH][RFC] XFS: Fix mem leak and possible NULL deref in xfs_setattr_nonsize()
From: Jesper Juhl <jj@xxxxxxxxxxxxx>
Date: Mon, 6 Feb 2012 21:44:45 +0100 (CET)
Cc: xfs@xxxxxxxxxxx, xfs-masters@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Ben Myers <bpm@xxxxxxx>, Alex Elder <elder@xxxxxxxxxx>, Raghavendra D Prabhu <raghu.prabhu13@xxxxxxxxx>
In-reply-to: <20120206062319.GB12836@dastard>
References: <alpine.LNX.2.00.1202052220390.32529@xxxxxxxxxxxxxxxxxxxxxxxxx> <20120206062319.GB12836@dastard>
User-agent: Alpine 2.00 (LNX 1167 2008-08-23)
On Mon, 6 Feb 2012, Dave Chinner wrote:

> On Sun, Feb 05, 2012 at 10:23:44PM +0100, Jesper Juhl wrote:
> > In xfs_setattr_nonsize(), xfs_trans_alloc() gets its memory from
> > _xfs_trans_alloc() which gets it from kmem_zone_zalloc() which may
> > fail and return NULL. So this:
> > 
> >     tp = xfs_trans_alloc(mp, XFS_TRANS_SETATTR_NOT_SIZE);
> > 
> > may result in a NULL 'tp'.
> > If it does, then the call:
> > 
> >     error = xfs_trans_reserve(tp, 0, XFS_ICHANGE_LOG_RES(mp), 0, 0, 0);
> > 
> > with a NULL 'tp' will explode, since xfs_trans_reserve() dereferences
> > its first argument unconditionally.
> 
> xfs_trans_alloc() can't fail. It will sleep forever until the memory
> allocation succeeds.
> 
> There's 35 other places in XFS where this xfs_trans_alloc/
> xfs_trans_reserve pattern occurs - none of them check whether tp is
> null, either.
> 
> > And if the memory allocation for 'tp' goes well (and thus
> > xfs_trans_reserve() does not explode) then we may leak the memory
> > allocated to 'tp' if xfs_trans_reserve() returns error.
> 
> yes, that's a problem, though will only happen if a filesystem
> shutdown occurs between the start of the function and that check.
> 
> > 
> > I believe this patch should fix both issues, but I'm not intimate with
> > the XFS code at all, so there can easily be something I overlooked or
> > something that should be done differently than what I did.
> 
> Only need to fix the leak of tp.
> 
Ok.
Thank you for the detailed explanation.
I believe the patch below should do the trick.


From: Jesper Juhl <jj@xxxxxxxxxxxxx>
Date: Sun, 5 Feb 2012 22:11:30 +0100
Subject: [PATCH] XFS: Fix mem leak in xfs_setattr_nonsize()

If the memory allocation for 'tp' goes well then we will leak the
memory allocated to 'tp' if xfs_trans_reserve() returns error.

Signed-off-by: Jesper Juhl <jj@xxxxxxxxxxxxx>
---
 fs/xfs/xfs_iops.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index ab30253..2fc1600 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -576,8 +576,10 @@ xfs_setattr_nonsize(
 
        tp = xfs_trans_alloc(mp, XFS_TRANS_SETATTR_NOT_SIZE);
        error = xfs_trans_reserve(tp, 0, XFS_ICHANGE_LOG_RES(mp), 0, 0, 0);
-       if (error)
+       if (error) {
+               xfs_trans_cancel(tp, 0);
                goto out_dqrele;
+       }
 
        xfs_ilock(ip, XFS_ILOCK_EXCL);
 
-- 
1.7.9


-- 
Jesper Juhl <jj@xxxxxxxxxxxxx>       http://www.chaosbits.net/
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