Re: [PATCH v2] lzo: fix ip overrun during compress.

Yueyi Li
2018-12-05T03:08:03Z

Hi Markus,

Thanks for your review.

On 2018/12/4 18:20, Markus F.X.J. Oberhumer wrote:
> Hi,
>
> I don't think that address space wraparound is legal in C, but I
> understand that we are in kernel land and if you really want to
> compress the last virtual page 0xfffffffffffff000 the following
> small patch should fix that dubious case.

I guess the VA 0xfffffffffffff000 is available because KASLR be
enabled. For this case we can see:

crash> kmem 0xfffffffffffff000
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
ffffffbfffffffc0 1fffff000 ffffffff1655ecb9 7181fd5 2
8000000000064209 locked,uptodate,owner_priv_1,writeback,reclaim,swapbacked

> This also avoids slowing down the the hot path of the compression
> core function.
>
> Cheers,
> Markus
>
>
>
> diff --git a/lib/lzo/lzo1x_compress.c b/lib/lzo/lzo1x_compress.c
> index 236eb21167b5..959dec45f6fe 100644
> --- a/lib/lzo/lzo1x_compress.c
> +++ b/lib/lzo/lzo1x_compress.c
> @@ -224,8 +224,8 @@ int lzo1x_1_compress(const unsigned char *in, size_t in_len,
>
> while (l > 20) {
> size_t ll = l <= (M4_MAX_OFFSET + 1) ? l : (M4_MAX_OFFSET + 1);
> - uintptr_t ll_end = (uintptr_t) ip + ll;
> - if ((ll_end + ((t + ll) >> 5)) <= ll_end)
> + // check for address space wraparound
> + if (((uintptr_t) ip + ll + ((t + ll) >> 5)) <= (uintptr_t) ip)
> break;
> BUILD_BUG_ON(D_SIZE * sizeof(lzo_dict_t) > LZO1X_1_MEM_COMPRESS);
> memset(wrkmem, 0, D_SIZE * sizeof(lzo_dict_t));
I parsed panic ramdump and loaded CPU register values, can see:

-000|lzo1x_1_do_compress(
| in = 0xFFFFFFFFFFFFF000,
| ?,
| out = 0xFFFFFFFF2E2EE000,
| out_len = 0xFFFFFF801CAA3510,
| ?,
| wrkmem = 0xFFFFFFFF4EBC0000)
| dict = 0xFFFFFFFF4EBC0000
| op = 0x1
| ip = 0x9
| ii = 0x9
| in_end = 0x0
| ip_end = 0xFFFFFFFFFFFFFFEC
| m_len = 0
| m_off = 1922
-001|lzo1x_1_compress(
| in = 0xFFFFFFFFFFFFF000,
| in_len = 0,
| out = 0xFFFFFFFF2E2EE000,
| out_len = 0x00000001616FB7D0,
| wrkmem = 0xFFFFFFFF4EBC0000)
| ip = 0xFFFFFFFFFFFFF000
| op = 0xFFFFFFFF2E2EE000
| l = 4096
| t = 0
| ll = 4096

ll = l = in_len = 4096 in lzo1x_1_compress, so your patch is working
for this panic case, but, I`m
not sure, is it possible that in = 0xFFFFFFFFFFFFF000 and in_len < 4096?

Thanks,
Yueyi