cifs: read overflow in is_valid_oplock_break()

We need to verify that the "data_offset" is within bounds.

Reported-by: Dr Silvio Cesare of InfoSect <silvio.cesare@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index dacb2c05674c5d7f11f7c4c9144646a95039d106..6926685e513cf4a3691df7efba36eb3dcb578b83 100644 (file)
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -402,9 +402,17 @@ is_valid_oplock_break(char *buffer, struct TCP_Server_Info *srv)
                        (struct smb_com_transaction_change_notify_rsp *)buf;
                struct file_notify_information *pnotify;
                __u32 data_offset = 0;
+               size_t len = srv->total_read - sizeof(pSMBr->hdr.smb_buf_length);
+
                if (get_bcc(buf) > sizeof(struct file_notify_information)) {
                        data_offset = le32_to_cpu(pSMBr->DataOffset);
 
+                       if (data_offset >
+                           len - sizeof(struct file_notify_information)) {
+                               cifs_dbg(FYI, "invalid data_offset %u\n",
+                                        data_offset);
+                               return true;
+                       }
                        pnotify = (struct file_notify_information *)
                                ((char *)&pSMBr->hdr.Protocol + data_offset);
                        cifs_dbg(FYI, "dnotify on %s Action: 0x%x\n",