linux-kernel - [PATCH -next] GRE: Use strlcat() for size checking

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Message-Id: <1364410111-29418-1-git-send-email-geert@linux-m68k.org>
Date:	Wed, 27 Mar 2013 19:48:31 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Pravin B Shelar <pshelar@...ira.com>,
	"David S. Miller" <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-next@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH -next] GRE: Use strlcat() for size checking

On m68k, gcc tries to be smart and turns

    strncat(name, "%d", 2);

into a call to strlen() and a 16-bit store, causing a link failure,
as arch/m68k/include/asm/string.h provides strlen() using a macro:

    ERROR: "strlen" [net/ipv4/ip_tunnel.ko] undefined!

Use strlcat() instead to avoid this, which also allows to simplify the
check for buffer overflows.

Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
--
Compile-tested only

http://kisskb.ellerman.id.au/kisskb/buildresult/8462108/
---
 net/ipv4/ip_tunnel.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 9d96b68..8dbe672 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -284,12 +284,11 @@ static struct net_device *__ip_tunnel_create(struct net *net,
 	if (parms->name[0])
 		strlcpy(name, parms->name, IFNAMSIZ);
 	else {
-		if (strlen(ops->kind) + 3 >= IFNAMSIZ) {
+		strlcpy(name, ops->kind, IFNAMSIZ);
+		if (strlcat(name, "%d", IFNAMSIZ) >= IFNAMSIZ) {
 			err = -E2BIG;
 			goto failed;
 		}
-		strlcpy(name, ops->kind, IFNAMSIZ);
-		strncat(name, "%d", 2);
 	}
 
 	ASSERT_RTNL();
-- 
1.7.0.4

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