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

Dave Chinner
2012-02-06T06:23:22Z

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@fromorbit.com