[U-Boot] [PATCH 3/6] gzip: correctly bounds-check output buffer

Michal Simek
2013-11-08T15:40:21Z

On 11/08/2013 04:21 PM, Kees Cook wrote:
> On Fri, Nov 8, 2013 at 4:04 AM, Michal Simek <monstr@monstr.eu> wrote:
>> Hi Kees,
>>
>> On 08/16/2013 04:59 PM, Kees Cook wrote:
>>> The output buffer size must not be reset by the gzip decoder or there
>>> is a risk of overflowing memory during decompression.
>>>
>>> Signed-off-by: Kees Cook <keescook@chromium.org>
>>> Acked-by: Simon Glass <sjg@chromium.org>
>>> ---
>>> lib/gunzip.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/gunzip.c b/lib/gunzip.c
>>> index 9959781..35abfb3 100644
>>> --- a/lib/gunzip.c
>>> +++ b/lib/gunzip.c
>>> @@ -89,13 +89,13 @@ int zunzip(void *dst, int dstlen, unsigned char *src, unsigned long *lenp,
>>> s.avail_out = dstlen;
>>> do {
>>> r = inflate(&s, Z_FINISH);
>>> - if (r != Z_STREAM_END && r != Z_BUF_ERROR && stoponerr == 1) {
>>> + if (stoponerr == 1 && r != Z_STREAM_END &&
>>> + (s.avail_out == 0 || r != Z_BUF_ERROR)) {
>>> printf("Error: inflate() returned %d\n", r);
>>> inflateEnd(&s);
>>> return -1;
>>> }
>>> s.avail_in = *lenp - offset - (int)(s.next_out - (unsigned char*)dst);
>>> - s.avail_out = dstlen;
>>> } while (r == Z_BUF_ERROR);
>>> *lenp = s.next_out - (unsigned char *) dst;
>>> inflateEnd(&s);
>>>
>>
>> I have done u-boot upgrade to v2013.10 version and I see the problem with this patch
>> when I am trying to boot my zynq image.
>>
>> After reverting this patch everything works as expected.
>
> Eek, sorry this is causing you trouble!

no worries. Problem is on my side. Look below.

>> Here is the image I am using.
>> http://www.monstr.eu/20131108-image.ub
>
> Is there any way you can extract just the gzipped kernel from this
> image? I'm not sure how to get at it from this .ub file.

Sure just run imi. Then you will get data start address and length.
And you can use unzip command.

>> Below is the bootlog.
>>
>> Do you have any idea what can be wrong?
>> [...]
>> Uncompressing Kernel Image ... Error: inflate() returned -5
>> GUNZIP: uncompress, out-of-mem or overwrite error - must RESET board to recover
>> resetting ...
>
> Either my change is failing to detect end-of-buffer correctly, or it
> _is_, in which case this has uncovered an unsafe caller of gunzip.
> This is after the "Uncompressing" message, so it's this caller:
>
> case IH_COMP_GZIP:
> printf(" Uncompressing %s ... ", type_name);
> if (gunzip(load_buf, unc_len, image_buf, &image_len) != 0) {
> puts("GUNZIP: uncompress, out-of-mem or overwrite "
> "error - must RESET board to recover\n");
> if (boot_progress)
> bootstage_error(BOOTSTAGE_ID_DECOMP_IMAGE);
> return BOOTM_ERR_RESET;
> }
>
> *load_end = load + image_len;
> break;
>
> If the uncompressed length of the kernel image is larger than
> "unc_len", then this is catching a legitimate memory overflow. This is
> entirely controlled by CONFIG_SYS_BOOTM_LEN. Is it possible this is
> set too low for your build?

Ah yes, that's the issue. My image is 14MB and have just 16MB BOOTM_LEN.

Thanks for pointing to this.
Michal

--
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform

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