[PATCH 6.18.y 2/2] libceph: bound pg_{temp,upmap,upmap_items} length to CEPH_PG_MAX_SIZE

From: Xiang Mei <[email protected]>

[ Upstream commit 9f00f9cf2be293efe899db67dc5272e3a9c62717 ]

__decode_pg_temp() decodes an user-controlled length but only rejects
values large enough to overflow the allocation; it does not bound it to
CEPH_PG_MAX_SIZE. The helper backs both pg_temp and pg_upmap decoding, and
apply_upmap()/get_temp_osds() later copy the decoded list into the fixed-size
on-stack array struct ceph_osds.osds[CEPH_PG_MAX_SIZE]. A monitor that sends
an OSDMap with a pg_temp/pg_upmap entry longer than 32 thus causes a stack
out-of-bounds write.

An OSD set for a single PG can never exceed CEPH_PG_MAX_SIZE, so reject longer
entries at decode time. The bound is well below the old overflow threshold, so
it also covers the allocation-size overflow the previous check guarded against.

  BUG: KASAN: stack-out-of-bounds in ceph_pg_to_up_acting_osds
  Write of size 4 ... by task exploit
   kasan_report (mm/kasan/report.c:595)
   ceph_pg_to_up_acting_osds (net/ceph/osdmap.c:2617 net/ceph/osdmap.c:2833)
   calc_target (net/ceph/osd_client.c:1638)
   __submit_request (net/ceph/osd_client.c:2394)
   ceph_osdc_start_request (net/ceph/osd_client.c:2490)
   ceph_osdc_call (net/ceph/osd_client.c:5164)
   rbd_dev_image_probe (drivers/block/rbd.c:6899)
   do_rbd_add (drivers/block/rbd.c:7138)
   ...
  kernel BUG at net/ceph/osdmap.c:2670!

[ idryomov: do the same in __decode_pg_upmap_items() ]

Cc: [email protected]
Fixes: a303bb0e5834 ("libceph: introduce and switch to decode_pg_mapping()")
Reported-by: Weiming Shi <[email protected]>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <[email protected]>
Reviewed-by: Alex Markuze <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
 net/ceph/osdmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index d8dd8c1cf362e..9ec8bbb625384 100644
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -1440,7 +1440,7 @@ static struct ceph_pg_mapping *__decode_pg_temp(void **p, void *end,
 	ceph_decode_32_safe(p, end, len, e_inval);
 	if (len == 0 && incremental)
 		return NULL;	/* new_pg_temp: [] to remove */
-	if ((size_t)len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
+	if (len > CEPH_PG_MAX_SIZE)
 		return ERR_PTR(-EINVAL);
 
 	ceph_decode_need(p, end, len * sizeof(u32), e_inval);
@@ -1621,7 +1621,7 @@ static struct ceph_pg_mapping *__decode_pg_upmap_items(void **p, void *end,
 	u32 len, i;
 
 	ceph_decode_32_safe(p, end, len, e_inval);
-	if ((size_t)len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
+	if (len > CEPH_PG_MAX_SIZE)
 		return ERR_PTR(-EINVAL);
 
 	ceph_decode_need(p, end, 2 * len * sizeof(u32), e_inval);
-- 
2.53.0