cifs: fix integer overflow in match_server()

The echo_interval is not limited in any way during mounting,
which makes it possible to write a large number to it. This can
cause an overflow when multiplying ctx->echo_interval by HZ in
match_server().

Add constraints for echo_interval to smb3_fs_context_parse_param().

Found by Linux Verification Center (linuxtesting.org) with Svace.

Fixes: adfeb3e ("cifs: Make echo interval tunable")
Cc: stable@vger.kernel.org
Signed-off-by: Roman Smirnov <r.smirnov@omp.ru>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: RSmirnov512

fs/smb/client/fs_context.c

@@ -1383,6 +1383,11 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 		ctx->closetimeo = HZ * result.uint_32;
 		break;
 	case Opt_echo_interval:
+		if (result.uint_32 < SMB_ECHO_INTERVAL_MIN ||
+		    result.uint_32 > SMB_ECHO_INTERVAL_MAX) {
+			cifs_errorf(fc, "echo interval is out of bounds\n");
+			goto cifs_parse_mount_err;
+		}
 		ctx->echo_interval = result.uint_32;
 		break;
 	case Opt_snapshot: