[PATCH 6.19 46/49] xfs: fix UAF in xchk_btree_check_block_owner

Greg Kroah-Hartman
2026-02-13T13:51:35Z

From: Darrick J. Wong <djwong@kernel.org>

commit 1c253e11225bc5167217897885b85093e17c2217 upstream.

We cannot dereference bs->cur when trying to determine if bs->cur
aliases bs->sc->sa.{bno,rmap}_cur after the latter has been freed.
Fix this by sampling before type before any freeing could happen.
The correct temporal ordering was broken when we removed xfs_btnum_t.

Cc: r772577952@gmail.com
Cc: <stable@vger.kernel.org> # v6.9
Fixes: ec793e690f801d ("xfs: remove xfs_btnum_t")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Jiaming Zhang <r772577952@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/xfs/scrub/btree.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/xfs/scrub/btree.c
+++ b/fs/xfs/scrub/btree.c
@@ -370,12 +370,15 @@ xchk_btree_check_block_owner(
{
xfs_agnumber_t agno;
xfs_agblock_t agbno;
+ bool is_bnobt, is_rmapbt;
bool init_sa;
int error = 0;

if (!bs->cur)
return 0;

+ is_bnobt = xfs_btree_is_bno(bs->cur->bc_ops);
+ is_rmapbt = xfs_btree_is_rmap(bs->cur->bc_ops);
agno = xfs_daddr_to_agno(bs->cur->bc_mp, daddr);
agbno = xfs_daddr_to_agbno(bs->cur->bc_mp, daddr);

@@ -398,11 +401,11 @@ xchk_btree_check_block_owner(
* have to nullify it (to shut down further block owner checks) if
* self-xref encounters problems.
*/
- if (!bs->sc->sa.bno_cur && xfs_btree_is_bno(bs->cur->bc_ops))
+ if (!bs->sc->sa.bno_cur && is_bnobt)
bs->cur = NULL;

xchk_xref_is_only_owned_by(bs->sc, agbno, 1, bs->oinfo);
- if (!bs->sc->sa.rmap_cur && xfs_btree_is_rmap(bs->cur->bc_ops))
+ if (!bs->sc->sa.rmap_cur && is_rmapbt)
bs->cur = NULL;