Messages in this thread | | | Date | Mon, 16 Aug 2021 10:13:16 +0300 | From | Dan Carpenter <> | Subject | Re: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data |
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On Sat, Aug 14, 2021 at 05:17:44PM +0300, Pavel Skripkin wrote: > 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? >
I don't care. Sure. I'm also fine with leaving it as is. I've been using "idx + 2 >= sizeof()" enough recently that it has become an idiom for me. But that's probably a bias on my part.
I guess "idx + 3 > sizeof()" is probably the most readable. Moving the + 3 to the other side would prevent integer overflows but we're not concerned about that here and no need to over engineer things if it hurts readability.
regards, dan carpenter
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