bin will be forcibly converted to "struct dns_server_list_v1_header *", so it 
is necessary to compare datalen with sizeof(*v1).

Fixes: b946001d3bb1 ("keys, dns: Allow key types (eg. DNS) to be reclaimed immediately on expiry")
Reported-and-tested-by: syzbot+94bbb75204a05da3d89f@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <redacted>
---
 net/dns_resolver/dns_key.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 3233f4f25fed..15f19521021c 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c

@@ -104,7 +104,7 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
 
 	if (data[0] == 0) {
 		/* It may be a server list. */
-		if (datalen <= sizeof(*bin))
+		if (datalen <= sizeof(*v1))
 			return -EINVAL;
 
 		bin = (const struct dns_payload_header *)data;