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Date: Wed, 5 Oct 2022 13:27:59 -0600 From: David Ahern <dsahern@...nel.org> To: Ido Schimmel <idosch@...sch.org> Cc: kuba@...nel.org, davem@...emloft.net, pabeni@...hat.com, netdev@...r.kernel.org, Gwangun Jung <exsociety@...il.com> Subject: Re: [PATCH net] ipv4: Handle attempt to delete multipath route when fib_info contains an nh reference On 10/5/22 1:08 PM, Ido Schimmel wrote: > On Wed, Oct 05, 2022 at 12:12:57PM -0600, David Ahern wrote: >> Gwangun Jung reported a slab-out-of-bounds access in fib_nh_match: >> fib_nh_match+0xf98/0x1130 linux-6.0-rc7/net/ipv4/fib_semantics.c:961 >> fib_table_delete+0x5f3/0xa40 linux-6.0-rc7/net/ipv4/fib_trie.c:1753 >> inet_rtm_delroute+0x2b3/0x380 linux-6.0-rc7/net/ipv4/fib_frontend.c:874 >> >> Separate nexthop objects are mutually exclusive with the legacy >> multipath spec. Fix fib_nh_match to return if the config for the >> to be deleted route contains a multipath spec while the fib_info >> is using a nexthop object. > > Cool bug... Managed to reproduce with: > > # ip nexthop add id 1 blackhole > # ip route add 192.0.2.0/24 nhid 1 > # ip route del 192.0.2.0/24 nexthop via 198.51.100.1 nexthop via 198.51.100.2 that's what I did as well. > > Maybe add to tools/testing/selftests/net/fib_nexthops.sh ? I have one in my tree, but in my tests nothing blew up or threw an error message. It requires KASAN to be enabled otherwise the test does not trigger anything. > > Checked IPv6 and I don't think we can hit it there, but I will double > check tomorrow morning. > >> >> Fixes: 493ced1ac47c ("ipv4: Allow routes to use nexthop objects") >> Reported-by: Gwangun Jung <exsociety@...il.com> >> Signed-off-by: David Ahern <dsahern@...nel.org> >> --- >> net/ipv4/fib_semantics.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> > > There is already such a check above for the non-multipath check, maybe > we can just move it up to cover both cases? Something like: > > diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c > index 2dc97583d279..e9a7f70a54df 100644 > --- a/net/ipv4/fib_semantics.c > +++ b/net/ipv4/fib_semantics.c > @@ -888,13 +888,13 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi, > return 1; > } > > + /* cannot match on nexthop object attributes */ > + if (fi->nh) > + return 1; that should work as well. I went with the simplest change that would definitely not have a negative impact on backports. > + > if (cfg->fc_oif || cfg->fc_gw_family) { > struct fib_nh *nh; > > - /* cannot match on nexthop object attributes */ > - if (fi->nh) > - return 1; > - > nh = fib_info_nh(fi, 0); > if (cfg->fc_encap) { > if (fib_encap_match(net, cfg->fc_encap_type,
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