linux-kernel - [PATCH] net/dns_resolver: dns_query Modify parameter checking to avoid dead code

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Date:   Mon, 4 Jun 2018 14:40:31 +0800
From:   nixiaoming <nixiaoming@...wei.com>
To:     <davem@...emloft.net>, <dhowells@...hat.com>,
        <manuel.schoelling@....de>, <wang840925@...il.com>
CC:     <nixiaoming@...wei.com>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: [PATCH] net/dns_resolver: dns_query Modify parameter checking to avoid dead code

After commit 1a4240f4764a ("DNS: Separate out CIFS DNS Resolver code")
a dead code exists in function dns_query

code show as below:
	if (!name || namelen == 0)
		return -EINVAL;
	/*Now the value of "namelen" cannot be equal to 0*/
	....
	if (!namelen) /*The condition "!namelen"" cannot be true*/
		namelen = strnlen(name, 256); /*deadcode*/

Modify parameter checking to avoid dead code

Signed-off-by: nixiaoming <nixiaoming@...wei.com>
---
 net/dns_resolver/dns_query.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
index 49da670..f2acee2 100644
--- a/net/dns_resolver/dns_query.c
+++ b/net/dns_resolver/dns_query.c
@@ -81,7 +81,9 @@ int dns_query(const char *type, const char *name, size_t namelen,
 	kenter("%s,%*.*s,%zu,%s",
 	       type, (int)namelen, (int)namelen, name, namelen, options);
 
-	if (!name || namelen == 0)
+	if (!name || namelen < 3 || namelen > 255)
+		return -EINVAL;
+	if (namelen > strnlen(name, 256)) /*maybe only need part of name*/
 		return -EINVAL;
 
 	/* construct the query key description as "[<type>:]<name>" */
@@ -94,10 +96,6 @@ int dns_query(const char *type, const char *name, size_t namelen,
 		desclen += typelen + 1;
 	}
 
-	if (!namelen)
-		namelen = strnlen(name, 256);
-	if (namelen < 3 || namelen > 255)
-		return -EINVAL;
 	desclen += namelen + 1;
 
 	desc = kmalloc(desclen, GFP_KERNEL);
-- 
2.10.1