FAILED: patch "[PATCH] ceph: fix integer overflow in the snap trace bounds check" failed to apply to 5.10-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.10-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 <stable@vger.kernel.org>.

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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x b3bf89767e3ca9506f1c7167cac97c41ec254d42
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107062906-failed-5.10-b3bf89767e3c@kernel.org' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Thanks,
Sasha

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

From b3bf89767e3ca9506f1c7167cac97c41ec254d42 Mon Sep 17 00:00:00 2001
From: Xiang Mei <xmei5@asu.edu>
Date: Tue, 15 Sep 2026 14:40:27 -0700
Subject: [PATCH] ceph: fix integer overflow in the snap trace bounds check

ceph_update_snap_trace() bounds the two encoded snapid arrays that follow a
struct ceph_mds_snap_realm with sizeof(u64) * (num_snaps +
num_prior_parent_snaps).  Both counts come straight off the wire as __le32,
so the addition is evaluated in unsigned int and wraps before sizeof(u64)
promotes it to size_t: an MDS sending num_snaps = 1 and
num_prior_parent_snaps = 0xffffffff makes the sum zero and the check
degenerates to ceph_decode_need(&p, e, 0, bad), which always passes.
dup_array() then reads num_snaps * 8 bytes past the end of the message
front, which ceph_msg_new2() allocates at exactly front_len bytes.  An
unsolicited CEPH_MSG_CLIENT_SNAP reaches this from a malicious or
compromised MDS with no client-side action, as do the snaptraces carried in
an MDS reply and in a cap import.

Compute the length with size_add()/size_mul() so it saturates at SIZE_MAX
instead of wrapping, in the style fs/ceph/mdsmap.c already uses for
num_export_targets.

  BUG: KASAN: slab-out-of-bounds in dup_array (include/linux/unaligned.h:28 fs/ceph/snap.c:500)
  Read of size 8 at addr ffff8880102a16c8 by task kworker/1:2/129
  Workqueue: ceph-msgr ceph_con_workfn
  Call Trace:
   dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
   print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)
   kasan_report (mm/kasan/report.c:595)
   dup_array (include/linux/unaligned.h:28 fs/ceph/snap.c:500)
   ceph_update_snap_trace (fs/ceph/snap.c:836)
   ceph_handle_snap (fs/ceph/snap.c:1155)
   mds_dispatch (fs/ceph/mds_client.c:7234)
   ceph_con_process_message (net/ceph/messenger.c:1424)
   ceph_con_v1_try_read (net/ceph/messenger_v1.c:1430)
   ceph_con_workfn (net/ceph/messenger.c:1576)
   process_one_work (kernel/workqueue.c:3396)
   worker_thread (kernel/workqueue.c:3479 kernel/workqueue.c:3560)
   kthread (kernel/kthread.c:436)
   ret_from_fork (arch/x86/kernel/process.c:158)
   ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
  ...
  The buggy address is located 0 bytes to the right of
   allocated 72-byte region [ffff8880102a1680, ffff8880102a16c8)

Cc: stable@vger.kernel.org
Fixes: 963b61eb041e ("ceph: snapshot management")
Reported-by: co+ecaada42f806f629@bugs.sh
Assisted-by: LLM
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 fs/ceph/snap.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 498ffc1a91cb8..5c1540d95b8c3 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -788,6 +788,7 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
 	struct ceph_snap_realm *first_realm = NULL;
 	struct ceph_snap_realm *realm_to_rebuild = NULL;
 	struct ceph_client *client = mdsc->fsc->client;
+	size_t snaps_len;
 	int rebuild_snapcs;
 	int err = -ENOMEM;
 	int ret;
@@ -802,8 +803,10 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
 	ceph_decode_need(&p, e, sizeof(*ri), bad);
 	ri = p;
 	p += sizeof(*ri);
-	ceph_decode_need(&p, e, sizeof(u64)*(le32_to_cpu(ri->num_snaps) +
-			    le32_to_cpu(ri->num_prior_parent_snaps)), bad);
+	snaps_len = size_mul(size_add(le32_to_cpu(ri->num_snaps),
+				      le32_to_cpu(ri->num_prior_parent_snaps)),
+			     sizeof(u64));
+	ceph_decode_need(&p, e, snaps_len, bad);
 	snaps = p;
 	p += sizeof(u64) * le32_to_cpu(ri->num_snaps);
 	prior_parent_snaps = p;
-- 
2.53.0