ksmbd: fix wrong DataOffset validation of create context

commit 17d5b13 upstream.

If ->DataOffset of create context is 0, DataBuffer size is not correctly
validated. This patch change wrong validation code and consider tag
length in request.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-21824
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/smb/server/oplock.c

@@ -1492,7 +1492,7 @@ struct create_context *smb2_find_context_vals(void *open_req, const char *tag, i
 		    name_len < 4 ||
 		    name_off + name_len > cc_len ||
 		    (value_off & 0x7) != 0 ||
-		    (value_off && (value_off < name_off + name_len)) ||
+		    (value_len && value_off < name_off + (name_len < 8 ? 8 : name_len)) ||
 		    ((u64)value_off + value_len > cc_len))
 			return ERR_PTR(-EINVAL);