NULL pointer dereference in xfs_trans_binval() when mounting and operating a crafted xfs image

Commit Message

Eric Sandeen June 7, 2018, 10:01 p.m. UTC

On 6/7/18 3:41 PM, Xu, Wen wrote:
> Dear XFS developers,
> 
> There is a NULL pointer dereference in xfs_trans_binval() when mounting and operating a crafted xfs image in 4.17-rc7 w/ for-next branch found by fuzzing.

...

> - Reason
> https://elixir.bootlin.com/linux/latest/source/fs/xfs/xfs_trans_buf.c#L610
> bp is NULL when calling xfs_trans_binval().

Yep, it looks like xfs_da_shrink_inode can error out before allocating
bp (i.e. in this case with an out of bounds blkno).  Does this fix it?



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Comments

Xu, Wen June 7, 2018, 10:25 p.m. UTC | #1

I tested the patch that works.

Thanks,
Wen

> On Jun 7, 2018, at 6:01 PM, Eric Sandeen <[e-mail]> wrote:
> 
> if (bp && (xfs_da_shrink_inode(args, 0, bp) != 0))

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Darrick J. Wong June 8, 2018, 4:49 p.m. UTC | #2

On Thu, Jun 07, 2018 at 10:25:56PM +0000, Xu, Wen wrote:
> I tested the patch that works.

ok.  Eric, would you mind adding a tested-by to the patch and sending it
with '[PATCH]' subject as a separate thread?

--D

> Thanks,
> Wen
> 
> > On Jun 7, 2018, at 6:01 PM, Eric Sandeen <[e-mail]> wrote:
> > 
> > if (bp && (xfs_da_shrink_inode(args, 0, bp) != 0))
> 
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Patch

=========

xfs: don't call xfs_da_shrink_inode with NULL bp

xfs_attr3_leaf_create may have errored out before instantiating a buffer,
for example if the blkno is out of range.  In that case there is no work 
to do to remove it, and in fact xfs_da_shrink_inode will lead to an oops
if we try.

This also seems to fix a flaw where the original error from
xfs_attr3_leaf_create gets overwritten in the cleanup case, and it
removes a pointless assignment to bp which isn't used after this.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199969
Reported-by: Xu, Wen <[e-mail]>
Signed-off-by: Eric Sandeen <[e-mail]>
---

diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
index 2135b8e..397699d 100644
--- a/fs/xfs/libxfs/xfs_attr_leaf.c
+++ b/fs/xfs/libxfs/xfs_attr_leaf.c
@@ -803,9 +803,8 @@  STATIC void xfs_attr3_leaf_moveents(struct xfs_da_args *args,
 	ASSERT(blkno == 0);
 	error = xfs_attr3_leaf_create(args, blkno, &bp);
 	if (error) {
-		error = xfs_da_shrink_inode(args, 0, bp);
-		bp = NULL;
-		if (error)
+		/* xfs_attr3_leaf_create may not have instantiated a block */
+		if (bp && (xfs_da_shrink_inode(args, 0, bp) != 0))
 			goto out;
 		xfs_idata_realloc(dp, size, XFS_ATTR_FORK);	/* try to put */
 		memcpy(ifp->if_u1.if_data, tmpbuffer, size);	/* it back */