[PATCH v4] ksmbd: fix invalid request buffer access in compound

[Namjae Jeon <linkinjeon@kernel.org>]

Ronnie reported invalid request buffer access in chained command when
inserting garbage value to NextCommand of compound request.
This patch add validation check to avoid this issue.

Cc: Tom Talpey <tom@talpey.com>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Ralph Böhme <slow@samba.org>
Cc: Steve French <smfrench@gmail.com>
Reported-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---
  v2:
   - fix integer overflow from work->next_smb2_rcv_hdr_off.
  v3:
   - check next command offset and at least header size of next pdu at
     the same time.
  v4:
   - add next_cmd variable not to avoid repeat conversion.

 fs/ksmbd/smb2pdu.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index 90f867b9d560..301558a04298 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -459,13 +459,21 @@ static void init_chained_smb2_rsp(struct ksmbd_work *work)
 bool is_chained_smb2_message(struct ksmbd_work *work)
 {
 	struct smb2_hdr *hdr = work->request_buf;
-	unsigned int len;
+	unsigned int len, next_cmd;
 
 	if (hdr->ProtocolId != SMB2_PROTO_NUMBER)
 		return false;
 
 	hdr = ksmbd_req_buf_next(work);
-	if (le32_to_cpu(hdr->NextCommand) > 0) {
+	next_cmd = le32_to_cpu(hdr->NextCommand);
+	if (next_cmd > 0) {
+		if ((u64)work->next_smb2_rcv_hdr_off + next_cmd + 64 >
+		    get_rfc1002_len(work->request_buf)) {
+			pr_err("next command(%u) offset exceeds smb msg size\n",
+			       next_cmd);
+			return false;
+		}
+
 		ksmbd_debug(SMB, "got SMB2 chained command\n");
 		init_chained_smb2_rsp(work);
 		return true;
-- 
2.25.1