[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@linux-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

On Wed, 2013-03-27 at 19:48 +0100, Geert Uytterhoeven wrote:

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!

Perhaps you should fix the string library for m68k, then!

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

It looks like you're also fixing an off-by-one error: the maximum length
of ops->kind will be IFNAMSIZ - 3 (just enough to add "%d" and the null
terminator), rather than IFNAMSIZ - 4.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

From: Ben Hutchings <redacted>
Date: Wed, 27 Mar 2013 20:06:16 +0000

On Wed, 2013-03-27 at 19:48 +0100, Geert Uytterhoeven wrote:

quoted

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!

Perhaps you should fix the string library for m68k, then!

Right, this symbol really must be provided.

You cannot merely provide inlines.

The off-by-one error is seperate, but that should be fixed
differently.