FAILED: patch "[PATCH] ceph: validate MDS reply fragtree split array length" 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 8cab7e7461f81ea1e0fd45082b50bb3c04c0bb10
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107062912-failed-5.10-8cab7e7461f8@kernel.org' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Thanks,
Sasha

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

From 8cab7e7461f81ea1e0fd45082b50bb3c04c0bb10 Mon Sep 17 00:00:00 2001
From: sung byeongchan <tjdqudcks0424@naver.com>
Date: Thu, 8 Oct 2026 15:07:25 +0900
Subject: [PATCH] ceph: validate MDS reply fragtree split array length

parse_reply_info_in() advances over the fragtree split array using an
unchecked count multiplication.  On a 32-bit client, nsplits=0x20000000
wraps the byte length to zero, so the reply is accepted and
ceph_fill_fragtree() sorts far beyond the message front.

Compute the split length with size_mul() and require the complete array to
remain in the inode record before advancing the cursor.

The malformed reply faulted in frag_tree_split_cmp() twice on the tested
i386 baseline.  It was rejected without a fault twice after this change,
while a normal reply and a one-split control remained functional.

Cc: stable@vger.kernel.org
Fixes: 2f2dc053404f ("ceph: MDS client")
Assisted-by: LLM
Signed-off-by: sung byeongchan <tjdqudcks0424@naver.com>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 fs/ceph/mds_client.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 456330f1d3c53..de36c83e94c0d 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -15,6 +15,7 @@
 #include <linux/ktime.h>
 #include <linux/bitmap.h>
 #include <linux/mnt_idmapping.h>
+#include <linux/overflow.h>
 
 #include "super.h"
 #include "mds_client.h"
@@ -146,6 +147,7 @@ static int parse_reply_info_in(void **p, void *end,
 			       struct ceph_mds_client *mdsc)
 {
 	int err = 0;
+	size_t splits_len;
 	u8 struct_v = 0;
 	u8 struct_compat = 0;
 	u32 struct_len = 0;
@@ -166,9 +168,11 @@ static int parse_reply_info_in(void **p, void *end,
 
 	ceph_decode_need(p, end, sizeof(struct ceph_mds_reply_inode), bad);
 	info->in = *p;
-	*p += sizeof(struct ceph_mds_reply_inode) +
-		sizeof(*info->in->fragtree.splits) *
-		le32_to_cpu(info->in->fragtree.nsplits);
+	splits_len = size_mul(sizeof(*info->in->fragtree.splits),
+			      le32_to_cpu(info->in->fragtree.nsplits));
+	*p += sizeof(struct ceph_mds_reply_inode);
+	ceph_decode_need(p, end, splits_len, bad);
+	*p += splits_len;
 
 	ceph_decode_32_safe(p, end, info->symlink_len, bad);
 	ceph_decode_need(p, end, info->symlink_len, bad);
-- 
2.53.0