[PATCH] smb: client: reject short SESSION_SETUP responses

[Abdifatah Suruur <suruurism@gmail.com>]

smb2_check_message() accepts frames shorter than struct smb2_pdu when
the SMB2 status is non-zero, before the minimum-PDU check added by
b4694f269e66d. A 64-byte STATUS_MORE_PROCESSING_REQUIRED SESSION_SETUP
response is therefore accepted even though it cannot contain the
SecurityBufferOffset and SecurityBufferLength fields.

The parser then reads those fields from stale bytes left in the reused
receive buffer by an earlier frame. With a long stale
SecurityBufferLength, decode_ntlmssp_challenge() copies up to about
64 KB from beyond the receive object and sends the data back to the
server in the NTLMv2 AUTHENTICATE target info.

Reject short MPR SESSION_SETUP responses before the short-error path,
and validate SecurityBufferOffset + SecurityBufferLength against the
received response length before decoding the challenge.

The ordering bypass is not new: the short-error early return predates
b4694f269e66d, and the unvalidated SecurityBufferLength read predates
the 2016 raw NTLMSSP split in 166cea4dc3a4, so all supported stable
trees are affected. Reproduced on 6.6.87.2; the path is unchanged on
mainline.

Cc: stable@vger.kernel.org
Signed-off-by: Abdifatah Suruur <suruurism@gmail.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
---
 fs/smb/client/smb2misc.c | 16 ++++++++++++++++
 fs/smb/client/smb2pdu.c  |  9 +++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/fs/smb/client/smb2misc.c b/fs/smb/client/smb2misc.c
index 5e5cf92d1..e107d4e79 100644
--- a/fs/smb/client/smb2misc.c
+++ b/fs/smb/client/smb2misc.c
@@ -225,6 +225,22 @@ smb2_check_message(char *buf, unsigned int pdu_len, unsigned int len,
 		return 1;
 	}
 
+	/*
+	 * A SESSION_SETUP response that asks for more processing carries a
+	 * security blob and is parsed as a normal reply. Do not let the
+	 * short-error path below accept a frame that cannot hold the fixed
+	 * response fields; the minimum-PDU check later is unreachable once
+	 * the early return has accepted the frame.
+	 */
+	if (command == SMB2_SESSION_SETUP_HE &&
+	    shdr->Status == STATUS_MORE_PROCESSING_REQUIRED &&
+	    len < smb2_min_pdu_len[command]) {
+		cifs_server_dbg(VFS,
+				"SMB2 SESSION_SETUP response too short: %u < %zu\n",
+				len, smb2_min_pdu_len[command]);
+		return 1;
+	}
+
 	if (len < pdu_size) {
 		if ((len >= hdr_size)
 		    && (shdr->Status != 0)) {
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index 5d892300d..f276acf7b 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -1857,14 +1857,19 @@ SMB2_sess_auth_rawntlmssp_negotiate(struct SMB2_sess_data *sess_data)
 		goto out;
 
 	u16 boff = le16_to_cpu(rsp->SecurityBufferOffset);
+	u16 blen = le16_to_cpu(rsp->SecurityBufferLength);
 
 	if (offsetof(struct smb2_sess_setup_rsp, Buffer) != boff) {
 		cifs_dbg(VFS, "Invalid security buffer offset %d\n", boff);
 		rc = smb_EIO1(smb_eio_trace_sess_buf_off, boff);
 		goto out;
 	}
-	rc = decode_ntlmssp_challenge(rsp->Buffer,
-			le16_to_cpu(rsp->SecurityBufferLength), ses);
+	if ((u32)boff + blen > sess_data->iov[0].iov_len) {
+		cifs_dbg(VFS, "Invalid security buffer length %u\n", blen);
+		rc = -EINVAL;
+		goto out;
+	}
+	rc = decode_ntlmssp_challenge(rsp->Buffer, blen, ses);
 	if (rc)
 		goto out;
 
-- 
2.53.0