FAILED: patch "[PATCH] ksmbd: prevent stale data from being written by SMB2 WRITE" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x bc0e0f5ac1d7b044d403f859406b4b66d4b1ce9b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026110352-stung-radiation-169e@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From bc0e0f5ac1d7b044d403f859406b4b66d4b1ce9b Mon Sep 17 00:00:00 2001
From: Namjae Jeon <linkinjeon@kernel.org>
Date: Mon, 7 Sep 2026 13:35:51 +0900
Subject: [PATCH] ksmbd: prevent stale data from being written by SMB2 WRITE
 requests

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>

diff --git a/fs/smb/server/compress.c b/fs/smb/server/compress.c
index 5162fb84c755..3fcb3e44302e 100644
--- a/fs/smb/server/compress.c
+++ b/fs/smb/server/compress.c
@@ -65,6 +65,7 @@ static int __ksmbd_decompress_request(struct ksmbd_conn *conn,
 		return -ENOMEM;
 
 	*(__be32 *)out = cpu_to_be32(out_size);
+	out[out_size + 4] = 0;
 	rc = smb_compression_decompress(conn->compress_algorithm,
 					conn->compress_chained,
 					conn->compress_pattern,
diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c
index d211861ff86f..3f8cc4998da5 100644
--- a/fs/smb/server/connection.c
+++ b/fs/smb/server/connection.c
@@ -752,6 +752,7 @@ 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 18602a4759c0..c792ed5ebbd3 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -9276,23 +9276,25 @@ 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 = smb2_current_req_len(work, &req->hdr);
 
-	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) {
@@ -9579,14 +9581,21 @@ 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 = smb2_current_req_len(work, &req->hdr);
+
+		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);