cifs: Fix integer overflow while processing actimeo mount option

User-provided mount parameter actimeo of type u32 is intended to have
an upper limit, but before it is validated, the value is converted from
seconds to jiffies which can lead to an integer overflow.

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

Fixes: 6d20e84 ("cifs: add attribute cache timeout (actimeo) tunable")
Signed-off-by: Murad Masimov <m.masimov@mt-integration.ru>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/fs_context.c

@@ -1358,7 +1358,7 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 		ctx->acdirmax = HZ * result.uint_32;
 		break;
 	case Opt_actimeo:
-		if (HZ * result.uint_32 > CIFS_MAX_ACTIMEO) {
+		if (result.uint_32 > CIFS_MAX_ACTIMEO / HZ) {
 			cifs_errorf(fc, "timeout too large\n");
 			goto cifs_parse_mount_err;
 		}