pstore/zone: cap the maximum device size

Introduce an abritrary 128MiB cap to avoid malloc failures when using
a larger block device.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: WeiXiong Liao <gmpy.liaowx@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201016132047.3068029-2-hch@lst.de

fs/pstore/zone.c

@@ -1299,6 +1299,10 @@ int register_pstore_zone(struct pstore_zone_info *info)
 		pr_warn("total_size must be >= 4096\n");
 		return -EINVAL;
 	}
+	if (info->total_size > SZ_128M) {
+		pr_warn("capping size to 128MiB\n");
+		info->total_size = SZ_128M;
+	}
 
 	if (!info->kmsg_size && !info->pmsg_size && !info->console_size &&
 	    !info->ftrace_size) {