netdev - Re: [PATCH] tipc: avoid possible string overflow

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Message-Id: <20180330.095439.156028039710999285.davem@davemloft.net>
Date:   Fri, 30 Mar 2018 09:54:39 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     arnd@...db.de
Cc:     jon.maloy@...csson.com, ying.xue@...driver.com,
        parthasarathy.bhuvaragan@...csson.com, netdev@...r.kernel.org,
        tipc-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tipc: avoid possible string overflow

From: Arnd Bergmann <arnd@...db.de>
Date: Wed, 28 Mar 2018 16:02:04 +0200

> gcc points out that the combined length of the fixed-length inputs to
> l->name is larger than the destination buffer size:
> 
> net/tipc/link.c: In function 'tipc_link_create':
> net/tipc/link.c:465:26: error: '%s' directive writing up to 32 bytes into a region of size between 26 and 58 [-Werror=format-overflow=]
>   sprintf(l->name, "%s:%s-%s:unknown", self_str, if_name, peer_str);
>                           ^~                              ~~~~~~~~
> net/tipc/link.c:465:2: note: 'sprintf' output 11 or more bytes (assuming 75) into a destination of size 60
>   sprintf(l->name, "%s:%s-%s:unknown", self_str, if_name, peer_str);
> 
> Using snprintf() ensures that the destination is still a nul-terminated
> string in all cases. It's still theoretically possible that the string
> gets trunctated though, so this patch should be carefully reviewed to
> ensure that either truncation is impossible in practice, or that we're
> ok with the truncation.
> 
> Fixes: 25b0b9c4e835 ("tipc: handle collisions of 32-bit node address hash values")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Based upon the discussion here, it looks like Jon will fix this in a different
way by increasing the destination buffer size.