[PATCH v2 3/3] ksmbd: fix invalid request buffer access in compound request

[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: 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.

 fs/ksmbd/smb2pdu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index 1fe37ad4e5bc..cae796ea1148 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -466,6 +466,13 @@ bool is_chained_smb2_message(struct ksmbd_work *work)
 
 	hdr = ksmbd_req_buf_next(work);
 	if (le32_to_cpu(hdr->NextCommand) > 0) {
+		if ((u64)work->next_smb2_rcv_hdr_off + le32_to_cpu(hdr->NextCommand) >
+		    get_rfc1002_len(work->request_buf)) {
+			pr_err("next command(%u) offset exceeds smb msg size\n",
+			       hdr->NextCommand);
+			return false;
+		}
+
 		ksmbd_debug(SMB, "got SMB2 chained command\n");
 		init_chained_smb2_rsp(work);
 		return true;
-- 
2.25.1