[PATCH net-next v2] net/dns_resolver: use kasprintf + kmemdup_nul to simplify dns_query

[Thorsten Blum <thorsten.blum@linux.dev>]

Use kasprintf() for descriptions with a query type and kmemdup_nul()
otherwise to simplify dns_query().

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
Changes in v2:
- Reverse xmas tree (Jakub)
- v1: https://lore.kernel.org/lkml/20260528222030.1655010-2-thorsten.blum@linux.dev/
---
 net/dns_resolver/dns_query.c | 33 ++++++++-------------------------
 1 file changed, 8 insertions(+), 25 deletions(-)

diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
index c250d82cad96..14bee83cbe22 100644
--- a/net/dns_resolver/dns_query.c
+++ b/net/dns_resolver/dns_query.c
@@ -64,44 +64,27 @@ int dns_query(struct net *net,
 	      const char *options, char **_result, time64_t *_expiry,
 	      bool invalidate)
 {
-	struct key *rkey;
 	struct user_key_payload *upayload;
-	size_t typelen, desclen;
-	char *desc, *cp;
+	struct key *rkey;
 	int ret, len;
+	char *desc;
 
 	kenter("%s,%*.*s,%zu,%s",
 	       type, (int)namelen, (int)namelen, name, namelen, options);
 
 	if (!name || namelen < 3 || namelen > 255)
 		return -EINVAL;
+	if (type && *type == '\0')
+		return -EINVAL;
 
 	/* construct the query key description as "[<type>:]<name>" */
-	typelen = 0;
-	desclen = 0;
-	if (type) {
-		typelen = strlen(type);
-		if (typelen < 1)
-			return -EINVAL;
-		desclen += typelen + 1;
-	}
-
-	desclen += namelen + 1;
-
-	desc = kmalloc(desclen, GFP_KERNEL);
+	if (type)
+		desc = kasprintf(GFP_KERNEL, "%s:%.*s", type, (int)namelen, name);
+	else
+		desc = kmemdup_nul(name, namelen, GFP_KERNEL);
 	if (!desc)
 		return -ENOMEM;
 
-	cp = desc;
-	if (type) {
-		memcpy(cp, type, typelen);
-		cp += typelen;
-		*cp++ = ':';
-	}
-	memcpy(cp, name, namelen);
-	cp += namelen;
-	*cp = '\0';
-
 	if (!options)
 		options = "";
 	kdebug("call request_key(,%s,%s)", desc, options);