Messages in this thread |  | | From | B K Karthik <> | Date | Mon, 27 Jul 2020 10:49:43 +0530 | Subject | Re: [PATCH v2] net: ipv6: fix use-after-free Read in __xfrm6_tunnel_spi_lookup |
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On Mon, Jul 27, 2020 at 1:37 AM Cong Wang <xiyou.wangcong@gmail.com> wrote: > > On Sat, Jul 25, 2020 at 11:12 PM B K Karthik <bkkarthik@pesu.pes.edu> wrote: > > > > On Sun, Jul 26, 2020 at 11:05 AM Cong Wang <xiyou.wangcong@gmail.com> wrote: > > > > > > On Sat, Jul 25, 2020 at 8:09 PM B K Karthik <bkkarthik@pesu.pes.edu> wrote: > > > > @@ -103,10 +103,10 @@ static int __xfrm6_tunnel_spi_check(struct net *net, u32 spi) > > > > { > > > > struct xfrm6_tunnel_net *xfrm6_tn = xfrm6_tunnel_pernet(net); > > > > struct xfrm6_tunnel_spi *x6spi; > > > > - int index = xfrm6_tunnel_spi_hash_byspi(spi); > > > > + int index = xfrm6_tunnel_spi_hash_byaddr((const xfrm_address_t *)spi); > > > > > > > > hlist_for_each_entry(x6spi, > > > > - &xfrm6_tn->spi_byspi[index], > > > > + &xfrm6_tn->spi_byaddr[index], > > > > list_byspi) { > > > > if (x6spi->spi == spi) > > > > > > How did you convince yourself this is correct? This lookup is still > > > using spi. :) > > > > I'm sorry, but my intention behind writing this patch was not to fix > > the UAF, but to fix a slab-out-of-bound. > > Odd, your $subject is clearly UAF, so is the stack trace in your changelog. > :) > > > > If required, I can definitely change the subject line and resend the > > patch, but I figured this was correct for > > https://syzkaller.appspot.com/bug?id=058d05f470583ab2843b1d6785fa8d0658ef66ae > > . since that particular report did not have a reproducer, > > Dmitry Vyukov <dvyukov@google.com> suggested that I test this patch on > > other reports for xfrm/spi . > > You have to change it to avoid misleading.
I will do that once somebody tells me this patch is reasonable to avoid wasting people's time. > > > > > Forgive me if this was the wrong way to send a patch for that > > particular report, but I guessed since the reproducer did not trigger > > the crash > > for UAF, I would leave the subject line as 'fix UAF' :) > > > > xfrm6_spi_hash_by_hash seemed more convincing because I had to prevent > > a slab-out-of-bounds because it uses ipv6_addr_hash. > > It would be of great help if you could help me understand how this was > > able to fix a UAF. > > Sure, you just avoid a pointer deref, which of course can fix the UAF, > but I still don't think it is correct in any aspect.
I saw a function call being made to tomoyo_check_acl(). the next thing happening is a kfree(). Also, spi_hash_byspi just returns spi % XFRM6_TUNNEL_SPI_BYSPI_HSIZE .
I'm a mentee, hence I would say my knowledge is very limited, please let me know if I am making a horrible mistake somewhere, but return (__force u32)(a->s6_addr32[0] ^ a->s6_addr32[1] ^ a->s6_addr32[2] ^ a->s6_addr32[3]); seems like a better because as David S. Miller <davem@davemloft.net> said "It is doing a XOR on all bits of an IPv6 address, it is doing more bit shifting which the existing hash was ignoring" .
Please help me understand this better if I am going wrong.
> > Even if it is a OOB, you still have to explain why it happened. Once > again, I can't see how it could happen either. > > > > > > > > > More importantly, can you explain how UAF happens? Apparently > > > the syzbot stack traces you quote make no sense at all. I also > > > looked at other similar reports, none of them makes sense to me. > > > > Forgive me, but I do not understand what you mean by the stack traces > > (this or other similar reports) "make no sense". > > Because the stack trace in your changelog clearly shows it is allocated > in tomoyo_init_log(), which is a buffer in struct tomoyo_query, but > none of xfrm paths uses it. Or do you see anything otherwise?
Aren't there indirect inet calls and netfilter hooks? I'm sorry I do not see anything otherwise. Please help me understand.
thanks,
karthik
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