[PATCH 5.15.y] ceph: fix 32-bit overflow in readdir reply count check

[Sasha Levin <sashal@kernel.org>]

From: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>

[ Upstream commit 52913831ba56efceaafd80b501d68fa00f79bde6 ]

parse_reply_info_readdir() checks how many entries are in a readdir
reply by computing the end pointer of the decoded array. That pointer
addition can wrap on 32-bit kernels and let an oversized count pass the
check. For example, a count of 0x40000000 with 156-byte entries wraps
to a zero offset, so the decoder can write past the preallocated buffer.

Check the count against the number of entries that fit in the allocation
before publishing dir_nr. Reject oversized replies through the existing
error path.

Cc: stable@vger.kernel.org
Fixes: 54008399dc0c ("ceph: preallocate buffer for readdir reply")
Assisted-by: LLM
Signed-off-by: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
[ sashal: adjusted error-path context to match pr_err() without WARN_ON(1) ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ceph/mds_client.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index d1bac25eb3e72..e5040a67a14f7 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -363,10 +363,8 @@ static int parse_reply_info_readdir(void **p, void *end,
 		goto done;
 
 	BUG_ON(!info->dir_entries);
-	if ((unsigned long)(info->dir_entries + num) >
-	    (unsigned long)info->dir_entries + info->dir_buf_size) {
+	if (num > info->dir_buf_size / sizeof(*info->dir_entries)) {
 		pr_err("dir contents are larger than expected\n");
-		WARN_ON(1);
 		goto bad;
 	}
 
-- 
2.53.0