netdev - RE: [PATCH 1/5] net: ipv4: using strlcpy instead of strncpy

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B729D@saturn3.aculab.com>
Date:	Thu, 20 Jun 2013 12:17:55 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Zhao Hongjiang" <zhaohongjiang@...wei.com>, <davem@...emloft.net>
Cc:	<kuznet@....inr.ac.ru>, <jmorris@...ei.org>,
	<yoshfuji@...ux-ipv6.org>, <kaber@...sh.net>,
	<netdev@...r.kernel.org>
Subject: RE: [PATCH 1/5] net: ipv4: using strlcpy instead of strncpy

> for NUL terminated string, need alway set '\0' in the end.
> 
> Signed-off-by: Zhao Hongjiang <zhaohongjiang@...wei.com>
> ---
>  net/ipv4/tcp_cong.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
> index 019c238..3280234 100644
> --- a/net/ipv4/tcp_cong.c
> +++ b/net/ipv4/tcp_cong.c
> @@ -170,7 +170,7 @@ void tcp_get_default_congestion_control(char *name)
> 
>  	rcu_read_lock();
>  	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
> -	strncpy(name, ca->name, TCP_CA_NAME_MAX);
> +	strlcpy(name, ca->name, sizeof(name));
>  	rcu_read_unlock();
>  }

Did you actually test this? I think not!

Blindly changing strncpy() to strlcpy() isn't a good idea.
You actually need to worry about the length of both arrays
and whether the source is always 0 terminated.
(Any whether the target is required to be terminated.)
Also, if the target might get copied to user space whether
you might be leaking uninitialized kernel memory.

The one above is just plain wrong though.

	David



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