В ядре Linux устранена следующая уязвимость:
xfs: check for deleted cursors when revalidating two btrees
The free space and inode btree repair functions will rebuild both btrees
at the same time, after which it needs to evaluate both btrees to
подтвердите, что повреждения исчезли. However, Jiaming Zhang ran syzbot and produced a crash in the second
вызов xchk_allocbt. His root-cause analysis is as follows (with minor
исправления):
In xrep_revalidate_allocbt(), xchk_allocbt() is called twice (first
для BNOBT, второй для CNTBT).
Причина этой проблемы в том, что
first call nullified the cursor required by the second call. Let's first enter xrep_revalidate_allocbt() via following call chain:
xfs_file_ioctl() ->
xfs_ioc_scrubv_metadata() ->
xfs_scrub_metadata() ->
`sc->ops->repair_eval(sc)` ->
xrep_revalidate_allocbt()
xchk_allocbt() вызывается в этой функции дважды. При первом звонке:
/* Note that sc->sm->sm_type is XFS_SCRUB_TYPE_BNOPT now */
xchk_allocbt() ->
xchk_btree() ->
`bs->scrub_rec(bs, Recp)` ->
xchk_allocbt_rec() ->
xchk_allocbt_xref() ->
xchk_allocbt_xref_other()
since sm_type is XFS_SCRUB_TYPE_BNOBT, pur is set to &sc->sa.cnt_cur.
Kernel called xfs_alloc_get_rec() and returned -EFSCORRUPTED. Позвонить
цепочка:
xfs_alloc_get_rec() ->
xfs_btree_get_rec() ->
xfs_btree_check_block() ->
(XFS_IS_CORRUPT || XFS_TEST_ERROR), the former is false and the latter
верно, верните -EFSCORRUPTED. Это должно быть вызвано
ioctl$XFS_IOC_ERROR_INJECTION Я думаю.
Back to xchk_allocbt_xref_other(), after receiving -EFSCORRUPTED from
xfs_alloc_get_rec(), kernel called xchk_should_check_xref(). В этом
function, *curpp (points to sc->sa.cnt_cur) is nullified. Back to xrep_revalidate_allocbt(), since sc->sa.cnt_cur has been
nullified, it then triggered null-ptr-deref via xchk_allocbt() (second
вызов) -> xchk_btree().
Так. The bnobt revalidation failed on a cross-reference attempt, so we
deleted the cntbt cursor, and then crashed when we tried to revalidate
cntbt. Therefore, check for a null cntbt cursor before that
повторную проверку и отметить ремонт как незавершенный.
Также мы можем игнорировать
second tree entirely if the first tree was rebuilt but is already
коррумпированный. Apply the same fix to xrep_revalidate_iallocbt because it has the same
проблема.
Показать оригинальное описание (EN)
In the Linux kernel, the following vulnerability has been resolved: xfs: check for deleted cursors when revalidating two btrees The free space and inode btree repair functions will rebuild both btrees at the same time, after which it needs to evaluate both btrees to confirm that the corruptions are gone. However, Jiaming Zhang ran syzbot and produced a crash in the second xchk_allocbt call. His root-cause analysis is as follows (with minor corrections): In xrep_revalidate_allocbt(), xchk_allocbt() is called twice (first for BNOBT, second for CNTBT). The cause of this issue is that the first call nullified the cursor required by the second call. Let's first enter xrep_revalidate_allocbt() via following call chain: xfs_file_ioctl() -> xfs_ioc_scrubv_metadata() -> xfs_scrub_metadata() -> `sc->ops->repair_eval(sc)` -> xrep_revalidate_allocbt() xchk_allocbt() is called twice in this function. In the first call: /* Note that sc->sm->sm_type is XFS_SCRUB_TYPE_BNOPT now */ xchk_allocbt() -> xchk_btree() -> `bs->scrub_rec(bs, recp)` -> xchk_allocbt_rec() -> xchk_allocbt_xref() -> xchk_allocbt_xref_other() since sm_type is XFS_SCRUB_TYPE_BNOBT, pur is set to &sc->sa.cnt_cur. Kernel called xfs_alloc_get_rec() and returned -EFSCORRUPTED. Call chain: xfs_alloc_get_rec() -> xfs_btree_get_rec() -> xfs_btree_check_block() -> (XFS_IS_CORRUPT || XFS_TEST_ERROR), the former is false and the latter is true, return -EFSCORRUPTED. This should be caused by ioctl$XFS_IOC_ERROR_INJECTION I guess. Back to xchk_allocbt_xref_other(), after receiving -EFSCORRUPTED from xfs_alloc_get_rec(), kernel called xchk_should_check_xref(). In this function, *curpp (points to sc->sa.cnt_cur) is nullified. Back to xrep_revalidate_allocbt(), since sc->sa.cnt_cur has been nullified, it then triggered null-ptr-deref via xchk_allocbt() (second call) -> xchk_btree(). So. The bnobt revalidation failed on a cross-reference attempt, so we deleted the cntbt cursor, and then crashed when we tried to revalidate the cntbt. Therefore, check for a null cntbt cursor before that revalidation, and mark the repair incomplete. Also we can ignore the second tree entirely if the first tree was rebuilt but is already corrupt. Apply the same fix to xrep_revalidate_iallocbt because it has the same problem.