linux-kernel - Re: [RFT, PATCH v1 1/1] hexdump: truncate output in case of overflow

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Date:	Wed, 28 Oct 2015 15:24:32 +0200
From:	Aaro Koskinen <aaro.koskinen@...ia.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [RFT, PATCH v1 1/1] hexdump: truncate output in case of overflow

Hi,

On Wed, Oct 28, 2015 at 12:48:19PM +0200, Andy Shevchenko wrote:
> There is a classical off-by-one error in case when we try to place, for
> example, 1+1 bytes as hex in the buffer of size 6. The expected result is to
> get an output truncated, but in the reality we get 6 bytes filed followed by
> terminating NUL.
> 
> Change the logic how we fill the output in case of byte dumping into limited
> space. This will follow the snprintf() behaviour by truncating output even on
> half bytes.
> 
> Fixes: 114fc1afb2de (hexdump: make it return number of bytes placed in buffer)
> Reported-by: Aaro Koskinen <aaro.koskinen@...ia.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

Thanks, this fixes the crash with kmemleak for me:

Tested-by: Aaro Koskinen <aaro.koskinen@...ia.com>

A.

> ---
> Waiting for Aaro's Tested-by: tag, that's why RFT. Meanwhile I will update
> test-hexdump to cover all corner case in overflow.
> 
> Linus, it would be nice to promote the fix when we get Aaro's confirmation.
> 
>  lib/hexdump.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/hexdump.c b/lib/hexdump.c
> index 8d74c20..992457b 100644
> --- a/lib/hexdump.c
> +++ b/lib/hexdump.c
> @@ -169,11 +169,15 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
>  		}
>  	} else {
>  		for (j = 0; j < len; j++) {
> -			if (linebuflen < lx + 3)
> +			if (linebuflen < lx + 2)
>  				goto overflow2;
>  			ch = ptr[j];
>  			linebuf[lx++] = hex_asc_hi(ch);
> +			if (linebuflen < lx + 2)
> +				goto overflow2;
>  			linebuf[lx++] = hex_asc_lo(ch);
> +			if (linebuflen < lx + 2)
> +				goto overflow2;
>  			linebuf[lx++] = ' ';
>  		}
>  		if (j)
> -- 
> 2.6.1
> 
--
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