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Date: Wed, 5 Oct 2022 22:08:03 +0300 From: Ido Schimmel <idosch@...sch.org> To: David Ahern <dsahern@...nel.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 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 Maybe add to tools/testing/selftests/net/fib_nexthops.sh ? 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(+) > > diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c > index 2dc97583d279..17caa73f57e6 100644 > --- a/net/ipv4/fib_semantics.c > +++ b/net/ipv4/fib_semantics.c > @@ -926,6 +926,10 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi, > if (!cfg->fc_mp) > return 0; > > + /* multipath spec and nexthop id are mutually exclusive */ > + if (fi->nh) > + return 1; > + > rtnh = cfg->fc_mp; > remaining = cfg->fc_mp_len; 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; + 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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