[PATCH 6.1.y] ksmbd: prevent stale data from being written by SMB2 WRITE requests

[Sasha Levin <sashal@kernel.org>]

From: Namjae Jeon <linkinjeon@kernel.org>

[ Upstream commit bc0e0f5ac1d7b044d403f859406b4b66d4b1ce9b ]

Initialize the compatibility byte in request buffers without zeroing
the entire allocation. Keep the one-byte compatibility exception for
SMB2 messages so valid zero-length WRITE requests remain compatible,
and validate the data range in the WRITE handlers against the current
compound request before accessing it.

This prevents stale request-buffer data from being written to files or
sent to IPC pipes.

Fixes: 443d61d1fa9f ("ksmbd: allocate one more byte for implied bcc[0]")
Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-32436
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
[ sashal: replaced smb2_current_req_len() calls with inline calculations using NextCommand or the remaining request buffer length ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/server/connection.c |  1 +
 fs/smb/server/smb2pdu.c    | 34 +++++++++++++++++++++++++---------
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c
index 168292f73a843..28c60d3070a25 100644
--- a/fs/smb/server/connection.c
+++ b/fs/smb/server/connection.c
@@ -403,6 +403,7 @@ int ksmbd_conn_handler_loop(void *p)
 		if (!conn->request_buf)
 			break;
 
+		conn->request_buf[pdu_size + 4] = 0;
 		memcpy(conn->request_buf, hdr_buf, sizeof(hdr_buf));
 
 		/*
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 8d2f5e4e9ae3b..250fb3d0a4c64 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -6683,23 +6683,28 @@ static noinline int smb2_write_pipe(struct ksmbd_work *work)
 	int err = 0, ret = 0;
 	char *data_buf;
 	size_t length;
+	unsigned int data_offset, req_len;
 
 	WORK_BUFFERS(work, req, rsp);
 
 	length = le32_to_cpu(req->Length);
 	id = req->VolatileFileId;
+	data_offset = le16_to_cpu(req->DataOffset);
+	req_len = le32_to_cpu(req->hdr.NextCommand);
+	if (!req_len)
+		req_len = get_rfc1002_len(work->request_buf) -
+			work->next_smb2_rcv_hdr_off;
 
-	if ((u64)le16_to_cpu(req->DataOffset) + length >
-	    get_rfc1002_len(work->request_buf)) {
-		pr_err("invalid write data offset %u, smb_len %u\n",
-		       le16_to_cpu(req->DataOffset),
-		       get_rfc1002_len(work->request_buf));
+	if (data_offset < offsetof(struct smb2_write_req, Buffer) ||
+	    data_offset > req_len || length > req_len - data_offset) {
+		pr_err("invalid write data offset %u, length %zu, req_len %u\n",
+		       data_offset, length, req_len);
 		err = -EINVAL;
 		goto out;
 	}
 
 	data_buf = (char *)(((char *)&req->hdr.ProtocolId) +
-			   le16_to_cpu(req->DataOffset));
+			   data_offset);
 
 	rpc_resp = ksmbd_rpc_write(work->sess, id, data_buf, length);
 	if (rpc_resp) {
@@ -6850,14 +6855,25 @@ int smb2_write(struct ksmbd_work *work)
 		writethrough = true;
 
 	if (is_rdma_channel == false) {
-		if (le16_to_cpu(req->DataOffset) <
-		    offsetof(struct smb2_write_req, Buffer)) {
+		unsigned int data_offset = le16_to_cpu(req->DataOffset);
+		unsigned int req_len = le32_to_cpu(req->hdr.NextCommand);
+
+		if (!req_len)
+			req_len = get_rfc1002_len(work->request_buf) -
+				work->next_smb2_rcv_hdr_off;
+
+		if (data_offset < offsetof(struct smb2_write_req, Buffer) ||
+		    data_offset > req_len ||
+		    length > req_len - data_offset) {
+			ksmbd_debug(SMB,
+				    "invalid write data offset %u, length %zu, req_len %u\n",
+				    data_offset, length, req_len);
 			err = -EINVAL;
 			goto out;
 		}
 
 		data_buf = (char *)(((char *)&req->hdr.ProtocolId) +
-				    le16_to_cpu(req->DataOffset));
+				    data_offset);
 
 		ksmbd_debug(SMB, "filename %pD, offset %lld, len %zu\n",
 			    fp->filp, offset, length);
-- 
2.53.0