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.

Fixes: 54008399dc0c ("ceph: preallocate buffer for readdir reply")
Assisted-by: LLM
Signed-off-by: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>
---
 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 085ae0c..cd928fd 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -479,10 +479,8 @@ 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_client(cl, "dir contents are larger than expected\n");
-		WARN_ON(1);
 		goto bad;
 	}
 
-- 
2.47.3