Messages in this thread | | | Subject | Re: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data | From | Pavel Skripkin <> | Date | Sat, 14 Aug 2021 17:17:44 +0300 |
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On 8/14/21 3:23 AM, Kevin Dawson wrote: > On Fri, Aug 13, 2021 at 05:58:34PM +0300, Dan Carpenter wrote: >> On Fri, Aug 13, 2021 at 02:28:55PM +0300, Pavel Skripkin wrote: >> > Syzbot reported slab-out-of bounds write in decode_data(). >> > The problem was in missing validation checks. >> > >> > Syzbot's reproducer generated malicious input, which caused >> > decode_data() to be called a lot in sixpack_decode(). Since >> > rx_count_cooked is only 400 bytes and noone reported before, >> > that 400 bytes is not enough, let's just check if input is malicious >> > and complain about buffer overrun. >> > >> > ... >> > >> > diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c >> > index fcf3af76b6d7..f4ffc2a80ab7 100644 >> > --- a/drivers/net/hamradio/6pack.c >> > +++ b/drivers/net/hamradio/6pack.c >> > @@ -827,6 +827,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte) >> > return; >> > } >> > >> > + if (sp->rx_count_cooked + 3 >= sizeof(sp->cooked_buf)) { >> >> It should be + 2 instead of + 3. >> >> We write three bytes. idx, idx + 1, idx + 2. Otherwise, good fix! > > I would suggest that the statement be: > > if (sp->rx_count_cooked + 3 > sizeof(sp->cooked_buf)) { > > or even, because it's a buffer overrun test: > > if (sp->rx_count_cooked > sizeof(sp->cooked_buf) - 3) { >
Hmm, I think, it will be more straightforward for someone not aware about driver details.
@Dan, can I add your Reviewed-by tag to v3 and what do you think about Kevin's suggestion?
> This is because if there are three bytes being written, that is the number that should be obvious in the test. > > I haven't looked at the surrounding code and there may be some other consideration why the "+ 2 >=" rather than "+ 3 >" (and from the description of "idx, idx + 1, idx + 2", I suspect it's visual consistency), so if that is important, feel free to adjust as required. >
With regards, Pavel Skripkin
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