[syzbot] [net?] KASAN: slab-out-of-bounds Read in dns_resolver_preparse

[syzbot]

> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

want either no args or 2 args (repo, branch), got 5

>
> diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
> index 2a6d363763a2..f18ca02aa95a 100644
> --- a/net/dns_resolver/dns_key.c
> +++ b/net/dns_resolver/dns_key.c
> @@ -91,8 +91,6 @@ const struct cred *dns_resolver_cache;
>  static int
>  dns_resolver_preparse(struct key_preparsed_payload *prep)
>  {
> -	const struct dns_server_list_v1_header *v1;
> -	const struct dns_payload_header *bin;
>  	struct user_key_payload *upayload;
>  	unsigned long derrno;
>  	int ret;
> @@ -103,27 +101,28 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
>  		return -EINVAL;
>  
>  	if (data[0] == 0) {
> +		const struct dns_server_list_v1_header *v1;
> +
>  		/* It may be a server list. */
> -		if (datalen <= sizeof(*bin))
> +		if (datalen <= sizeof(*v1))
>  			return -EINVAL;
>  
> -		bin = (const struct dns_payload_header *)data;
> -		kenter("[%u,%u],%u", bin->content, bin->version, datalen);
> -		if (bin->content != DNS_PAYLOAD_IS_SERVER_LIST) {
> +		v1 = (const struct dns_server_list_v1_header *)data;
> +		kenter("[%u,%u],%u", v1->hdr.content, v1->hdr.version, datalen);
> +		if (v1->hdr.content != DNS_PAYLOAD_IS_SERVER_LIST) {
>  			pr_warn_ratelimited(
>  				"dns_resolver: Unsupported content type (%u)\n",
> -				bin->content);
> +				v1->hdr.content);
>  			return -EINVAL;
>  		}
>  
> -		if (bin->version != 1) {
> +		if (v1->hdr.version != 1) {
>  			pr_warn_ratelimited(
>  				"dns_resolver: Unsupported server list version (%u)\n",
> -				bin->version);
> +				v1->hdr.version);
>  			return -EINVAL;
>  		}
>  
> -		v1 = (const struct dns_server_list_v1_header *)bin;
>  		if ((v1->status != DNS_LOOKUP_GOOD &&
>  		     v1->status != DNS_LOOKUP_GOOD_WITH_BAD)) {
>  			if (prep->expiry == TIME64_MAX)
>