FAILED: patch "[PATCH] libceph: bound pg_{temp,upmap,upmap_items} length to" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 9f00f9cf2be293efe899db67dc5272e3a9c62717
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072927-cloud-mustang-1d03@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9f00f9cf2be293efe899db67dc5272e3a9c62717 Mon Sep 17 00:00:00 2001
From: Xiang Mei <[email protected]>
Date: Mon, 8 Jun 2026 21:40:09 -0700
Subject: [PATCH] libceph: bound pg_{temp,upmap,upmap_items} length to
CEPH_PG_MAX_SIZE

__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() ]

index 04036c047b8c..a4b0dd8672ec 100644
@@ -1438,7 +1438,7 @@ 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);

@@ -1619,7 +1619,7 @@ 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);

From: Andy Shevchenko <[email protected]>

[ Upstream commit 04d8712b079327409b09dee628378f9583e2e035 ]

In a few cases the code compares 32-bit value to a SIZE_MAX derived constant which is much higher than that value on 64-bit platforms, Clang, in particular, is not happy about this

net/ceph/osdmap.c:1441:10: error: result of comparison of constant 4611686018427387891 with expression of type 'u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
1441 | if (len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))

      |             ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net/ceph/osdmap.c:1624:10: error: result of comparison of constant 2305843009213693945 with expression of type 'u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
 1624 |         if (len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
      |             ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this by casting to size_t. Note, that possible replacement of SIZE_MAX by U32_MAX may lead to the behaviour changes on the corner cases.

Stable-dep-of: 9f00f9cf2be2 ("libceph: bound pg_{temp,upmap,upmap_items} length to CEPH_PG_MAX_SIZE")

---
 net/ceph/osdmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 30d75970be449..d8dd8c1cf362e 100644
@@ -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 (len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
+	if ((size_t)len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
 		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 (len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
+	if ((size_t)len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
 		return ERR_PTR(-EINVAL);
 
 	ceph_decode_need(p, end, 2 * len * sizeof(u32), e_inval);

2.53.0

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() ]

---
 net/ceph/osdmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index d8dd8c1cf362e..9ec8bbb625384 100644
@@ -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