linux-kernel - Re: [PATCH] initramfs: prevent buffer overflow when unpacking to rootfs

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Message-Id: <20100402145702.fb9ccfdc.akpm@linux-foundation.org>
Date:	Fri, 2 Apr 2010 14:57:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Aaro Koskinen <aaro.koskinen@....fi>
Cc:	linux-kernel@...r.kernel.org, hsweeten@...ionengravers.com,
	hpa@...or.com, eric.piel@...mplin-utc.net,
	stable <stable@...nel.org>
Subject: Re: [PATCH] initramfs: prevent buffer overflow when unpacking to
 rootfs

On Thu,  1 Apr 2010 12:45:46 +0300
Aaro Koskinen <aaro.koskinen@....fi> wrote:

> Garbage in the initrd memory area may result in the unpack routine
> accessing memory outside the buffer. The patch adds a check that the
> specified area size is not exceeded.
> 
> Signed-off-by: Aaro Koskinen <aaro.koskinen@....fi>
> Cc: stable <stable@...nel.org>
> ---
> 
> The patch prevents the following kernel panic on Amstrad E3:
> 
> 	Unpacking initramfs...
> 	Unable to handle kernel paging request at virtual address c20121a7
>
> ...
>
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -460,6 +460,8 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len)
>  		}
>  		if (state != Reset)
>  			error("junk in compressed archive");
> +		if (my_inptr >= len)
> +			break;
>  		this_header = saved_offset + my_inptr;
>  		buf += my_inptr;
>  		len -= my_inptr;

OK, so if I'm understanding this right, the call to

	decompress(buf, len, NULL, flush_buffer, NULL, &my_inptr, error);

has gone and generated more output data than it was asked to generate?

If so, isn't that a bug in the decompressor?  Which one is your system using?

[ wonders why my_inptr is static, and why the sixth arg to decompress_fn
  takes an int* while callers are passing in an unsigned* ]

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