netdev - Re: [PATCH net-next] pktgen: convert safe uses of strncpy() to strcpy() to avoid string truncation warning

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Date:   Thu, 19 Jul 2018 07:24:33 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     jakub.kicinski@...ronome.com
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] pktgen: convert safe uses of strncpy() to
 strcpy() to avoid string truncation warning

From: Jakub Kicinski <jakub.kicinski@...ronome.com>
Date: Tue, 17 Jul 2018 14:32:24 -0700

> GCC 8 complains:
> 
> net/core/pktgen.c: In function ‘pktgen_if_write’:
> net/core/pktgen.c:1419:4: warning: ‘strncpy’ output may be truncated copying between 0 and 31 bytes from a string of length 127 [-Wstringop-truncation]
>     strncpy(pkt_dev->src_max, buf, len);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/core/pktgen.c:1399:4: warning: ‘strncpy’ output may be truncated copying between 0 and 31 bytes from a string of length 127 [-Wstringop-truncation]
>     strncpy(pkt_dev->src_min, buf, len);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/core/pktgen.c:1290:4: warning: ‘strncpy’ output may be truncated copying between 0 and 31 bytes from a string of length 127 [-Wstringop-truncation]
>     strncpy(pkt_dev->dst_max, buf, len);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/core/pktgen.c:1268:4: warning: ‘strncpy’ output may be truncated copying between 0 and 31 bytes from a string of length 127 [-Wstringop-truncation]
>     strncpy(pkt_dev->dst_min, buf, len);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> There is no bug here, but the code is not perfect either.  It copies
> sizeof(pkt_dev->/member/) - 1 from user space into buf, and then does
> a strcmp(pkt_dev->/member/, buf) hence assuming buf will be null-terminated
> and shorter than pkt_dev->/member/ (pkt_dev->/member/ is never
> explicitly null-terminated, and strncpy() doesn't have to null-terminate
> so the assumption must be on buf).  The use of strncpy() without explicit
> null-termination looks suspicious.  Convert to use straight strcpy().
> 
> strncpy() would also null-pad the output, but that's clearly unnecessary
> since the author calls memset(pkt_dev->/member/, 0, sizeof(..)); prior
> to strncpy(), anyway.
> 
> While at it format the code for "dst_min", "dst_max", "src_min" and
> "src_max" in the same way by removing extra new lines in one case.
> 
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Reviewed-by: Jiong Wang <jiong.wang@...ronome.com>

Applied, thanks Jakub.