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

Jesper Juhl
2012-02-06T20:44:16Z

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@chaosbits.net>
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@chaosbits.net>
---
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