[PATCH 6.3 278/286] ksmbd: fix slab-out-of-bounds read in smb2_handle_negotiate

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From: Kuan-Ting Chen <h3xrabbit@xxxxxxxxx>

commit d738950f112c8f40f0515fe967db998e8235a175 upstream.

Check request_buf length first to avoid out-of-bounds read by
req->DialectCount.

[ 3350.990282] BUG: KASAN: slab-out-of-bounds in smb2_handle_negotiate+0x35d7/0x3e60
[ 3350.990282] Read of size 2 at addr ffff88810ad61346 by task kworker/5:0/276
[ 3351.000406] Workqueue: ksmbd-io handle_ksmbd_work
[ 3351.003499] Call Trace:
[ 3351.006473]  <TASK>
[ 3351.006473]  dump_stack_lvl+0x8d/0xe0
[ 3351.006473]  print_report+0xcc/0x620
[ 3351.006473]  kasan_report+0x92/0xc0
[ 3351.006473]  smb2_handle_negotiate+0x35d7/0x3e60
[ 3351.014760]  ksmbd_smb_negotiate_common+0x7a7/0xf00
[ 3351.014760]  handle_ksmbd_work+0x3f7/0x12d0
[ 3351.014760]  process_one_work+0xa85/0x1780

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kuan-Ting Chen <h3xrabbit@xxxxxxxxx>
Acked-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/ksmbd/smb2pdu.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -1081,16 +1081,16 @@ int smb2_handle_negotiate(struct ksmbd_w
 		return rc;
 	}
 
-	if (req->DialectCount == 0) {
-		pr_err("malformed packet\n");
+	smb2_buf_len = get_rfc1002_len(work->request_buf);
+	smb2_neg_size = offsetof(struct smb2_negotiate_req, Dialects);
+	if (smb2_neg_size > smb2_buf_len) {
 		rsp->hdr.Status = STATUS_INVALID_PARAMETER;
 		rc = -EINVAL;
 		goto err_out;
 	}
 
-	smb2_buf_len = get_rfc1002_len(work->request_buf);
-	smb2_neg_size = offsetof(struct smb2_negotiate_req, Dialects);
-	if (smb2_neg_size > smb2_buf_len) {
+	if (req->DialectCount == 0) {
+		pr_err("malformed packet\n");
 		rsp->hdr.Status = STATUS_INVALID_PARAMETER;
 		rc = -EINVAL;
 		goto err_out;





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