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

To: Jesper Juhl <jj@xxxxxxxxxxxxx>
Subject: Re: [PATCH][RFC] XFS: Fix mem leak and possible NULL deref in xfs_setattr_nonsize()
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 6 Feb 2012 17:23:19 +1100
Cc: xfs@xxxxxxxxxxx, xfs-masters@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Ben Myers <bpm@xxxxxxx>, Alex Elder <elder@xxxxxxxxxx>
In-reply-to: <alpine.LNX.2.00.1202052220390.32529@xxxxxxxxxxxxxxxxxxxxxxxxx>
References: <alpine.LNX.2.00.1202052220390.32529@xxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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