Re: [PATCH][RFC] XFS: Fix mem leak and possible NULL deref inxfs_setattr_nonsize()

[Raghavendra D Prabhu]

Hi,


* On Sun, Feb 05, 2012 at 10:23:44PM +0100, Jesper Juhl <jj@xxxxxxxxxxxxx> 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.
>
> 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.
>
> 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.
>
> Signed-off-by: Jesper Juhl <jj@xxxxxxxxxxxxx>
> ---
> fs/xfs/xfs_iops.c |    7 ++++++-
> 1 files changed, 6 insertions(+), 1 deletions(-)
>
> Note:
>  Please review carefully before applying.
>  Especially since I don't currently have any XFS filesystems to test
>  this on, nor any clear idea of a good way to actually test this if I
>  had. So this patch is compile tested only on my end.
>
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index ab30253..194c9d7 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -575,9 +575,14 @@ xfs_setattr_nonsize(
> 	}
>
> 	tp = xfs_trans_alloc(mp, XFS_TRANS_SETATTR_NOT_SIZE);
> +	if (!tp)
> +		goto out_dqrele;
> +
> 	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
>
>
> Please CC me on replies.
>
> --
> Jesper Juhl <jj@xxxxxxxxxxxxx>       http://www.chaosbits.net/
> Don't top-post http://www.catb.org/jargon/html/T/top-post.html
> Plain text mails only, please.
>
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The first one won't be triggered because kmem_zone_alloc (the 
last one in call chain) checks for 

    if (ptr || (flags & (KM_MAYFAIL|KM_NOSLEEP)))

whereas xfs_trans_alloc  calls _xfs_trans_alloc with KM_SLEEP, 
also all other callers of _xfs_trans_alloc call it with KM_SLEEP 
(except one which calls with KM_NOFS), so it looks like we are 
safe there, it keeps spinning till it finds mem.


As far as second one is concerned, looks fine, though this one 
should also do the same.

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index ab30253..d331f5b 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -730,9 +730,9 @@ xfs_setattr_nonsize(
        return 0;

out_trans_cancel:
-       xfs_trans_cancel(tp, 0);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
out_dqrele:
+       xfs_trans_cancel(tp, 0);
        xfs_qm_dqrele(udqp);
        xfs_qm_dqrele(gdqp);
        return error;



Regards,
--
Raghavendra Prabhu
GPG Id : 0xD72BE977
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