[PATCH v3] ksmbd: validate length in smb2_write()

[Marios Makassikis <mmakassikis@freebox.fr>]

The SMB2 Write packet contains data that is to be written
to a file or to a pipe. Depending on the client, there may
be padding between the header and the data field.
Currently, the length is validated only in the case padding
is present.

Since the DataOffset field always points to the beginning
of the data, there is no need to have a special case for
padding. By removing this, the length is validated in both
cases.

Additionally, fix the length check: DataOffset and Length
fields are relative to the SMB header start, while the packet
length returned by get_rfc1002_len() includes 4 additional
bytes.

Signed-off-by: Marios Makassikis <mmakassikis@freebox.fr>
---
Change since v2:
 - the length check was wrong, as it did not account for the rfc1002
 header in work->request_buf.

 fs/ksmbd/smb2pdu.c | 49 ++++++++++++++++++----------------------------
 1 file changed, 19 insertions(+), 30 deletions(-)

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index 16c803a9d996..23b47e505e2b 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -6328,23 +6328,18 @@ static noinline int smb2_write_pipe(struct ksmbd_work *work)
 	length = le32_to_cpu(req->Length);
 	id = req->VolatileFileId;
 
-	if (le16_to_cpu(req->DataOffset) ==
-	    offsetof(struct smb2_write_req, Buffer)) {
-		data_buf = (char *)&req->Buffer[0];
-	} else {
-		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));
-			err = -EINVAL;
-			goto out;
-		}
-
-		data_buf = (char *)(((char *)&req->hdr.ProtocolId) +
-				le16_to_cpu(req->DataOffset));
+	if ((u64)le16_to_cpu(req->DataOffset) + length >
+	    get_rfc1002_len(work->request_buf) - 4) {
+		pr_err("invalid write data offset %u, smb_len %u\n",
+		       le16_to_cpu(req->DataOffset),
+		       get_rfc1002_len(work->request_buf));
+		err = -EINVAL;
+		goto out;
 	}
 
+	data_buf = (char *)(((char *)&req->hdr.ProtocolId) +
+			   le16_to_cpu(req->DataOffset));
+
 	rpc_resp = ksmbd_rpc_write(work->sess, id, data_buf, length);
 	if (rpc_resp) {
 		if (rpc_resp->flags == KSMBD_RPC_ENOTIMPLEMENTED) {
@@ -6489,22 +6484,16 @@ int smb2_write(struct ksmbd_work *work)
 
 	if (req->Channel != SMB2_CHANNEL_RDMA_V1 &&
 	    req->Channel != SMB2_CHANNEL_RDMA_V1_INVALIDATE) {
-		if (le16_to_cpu(req->DataOffset) ==
-		    offsetof(struct smb2_write_req, Buffer)) {
-			data_buf = (char *)&req->Buffer[0];
-		} else {
-			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));
-				err = -EINVAL;
-				goto out;
-			}
-
-			data_buf = (char *)(((char *)&req->hdr.ProtocolId) +
-					le16_to_cpu(req->DataOffset));
+		if ((u64)le16_to_cpu(req->DataOffset) + length >
+		    get_rfc1002_len(work->request_buf) - 4) {
+			pr_err("invalid write data offset %u, smb_len %u\n",
+			       le16_to_cpu(req->DataOffset),
+			       get_rfc1002_len(work->request_buf));
+			err = -EINVAL;
+			goto out;
 		}
+		data_buf = (char *)(((char *)&req->hdr.ProtocolId) +
+				    le16_to_cpu(req->DataOffset));
 
 		ksmbd_debug(SMB, "flags %u\n", le32_to_cpu(req->Flags));
 		if (le32_to_cpu(req->Flags) & SMB2_WRITEFLAG_WRITE_THROUGH)
-- 
2.25.1