[PATCH v2] ksmbd: Annotate struct copychunk_ioctl_req with __counted_by_le()

[Thorsten Blum <thorsten.blum@linux.dev>]

Add the __counted_by_le compiler attribute to the flexible array member
Chunks to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Change the data type of the flexible array member Chunks from __u8[] to
struct srv_copychunk[] for ChunkCount to match the number of elements in
the Chunks array. (With __u8[], each srv_copychunk would occupy 24 array
entries and the __counted_by compiler attribute wouldn't be applicable.)

Use struct_size() to calculate the size of the copychunk_ioctl_req.

Read Chunks[0] after checking that ChunkCount is not 0.

Compile-tested only.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
Changes in v2:
- Change the data type of Chunks from __u8[] to struct srv_copychunk[]
  as suggested by Tom Talpey
- Use struct_size()
- Link to v1: https://lore.kernel.org/linux-kernel/20240924102243.239811-2-thorsten.blum@linux.dev/
---
 fs/smb/server/smb2pdu.c |  5 ++---
 fs/smb/server/smb2pdu.h | 14 +++++++-------
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 7121266daa02..62312c5e790e 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -7566,7 +7566,6 @@ static int fsctl_copychunk(struct ksmbd_work *work,
 	ci_rsp->TotalBytesWritten =
 		cpu_to_le32(ksmbd_server_side_copy_max_total_size());
 
-	chunks = (struct srv_copychunk *)&ci_req->Chunks[0];
 	chunk_count = le32_to_cpu(ci_req->ChunkCount);
 	if (chunk_count == 0)
 		goto out;
@@ -7574,12 +7573,12 @@ static int fsctl_copychunk(struct ksmbd_work *work,
 
 	/* verify the SRV_COPYCHUNK_COPY packet */
 	if (chunk_count > ksmbd_server_side_copy_max_chunk_count() ||
-	    input_count < offsetof(struct copychunk_ioctl_req, Chunks) +
-	     chunk_count * sizeof(struct srv_copychunk)) {
+	    input_count < struct_size(ci_req, Chunks, chunk_count)) {
 		rsp->hdr.Status = STATUS_INVALID_PARAMETER;
 		return -EINVAL;
 	}
 
+	chunks = &ci_req->Chunks[0];
 	for (i = 0; i < chunk_count; i++) {
 		if (le32_to_cpu(chunks[i].Length) == 0 ||
 		    le32_to_cpu(chunks[i].Length) > ksmbd_server_side_copy_max_chunk_size())
diff --git a/fs/smb/server/smb2pdu.h b/fs/smb/server/smb2pdu.h
index 73aff20e22d0..649dacf7e8c4 100644
--- a/fs/smb/server/smb2pdu.h
+++ b/fs/smb/server/smb2pdu.h
@@ -190,13 +190,6 @@ struct resume_key_ioctl_rsp {
 	__u8 Context[4]; /* ignored, Windows sets to 4 bytes of zero */
 } __packed;
 
-struct copychunk_ioctl_req {
-	__le64 ResumeKey[3];
-	__le32 ChunkCount;
-	__le32 Reserved;
-	__u8 Chunks[]; /* array of srv_copychunk */
-} __packed;
-
 struct srv_copychunk {
 	__le64 SourceOffset;
 	__le64 TargetOffset;
@@ -204,6 +197,13 @@ struct srv_copychunk {
 	__le32 Reserved;
 } __packed;
 
+struct copychunk_ioctl_req {
+	__le64 ResumeKey[3];
+	__le32 ChunkCount;
+	__le32 Reserved;
+	struct srv_copychunk Chunks[] __counted_by_le(ChunkCount);
+} __packed;
+
 struct copychunk_ioctl_rsp {
 	__le32 ChunksWritten;
 	__le32 ChunkBytesWritten;
-- 
2.46.1