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ipv6: fib6_select_path can not use out path for nexthop objects 

Brian reported a crash in IPv6 code when using rpfilter with a setup
running FRR and external nexthop objects. The root cause of the crash
is fib6_select_path setting fib6_nh in the result to NULL because of
an improper check for nexthop objects.

More specifically, rpfilter invokes ip6_route_lookup with flowi6_oif
set causing fib6_select_path to be called with have_oif_match set.
fib6_select_path has early check on have_oif_match and jumps to the
out label which presumes a builtin fib6_nh. This path is invalid for
nexthop objects; for external nexthops fib6_select_path needs to just
return if the fib6_nh has already been set in the result otherwise it
returns after the call to nexthop_path_fib6_result. Update the check
on have_oif_match to not bail on external nexthops.

Update selftests for this problem.

Fixes: f88d8ea67f ("ipv6: Plumb support for nexthop object in a fib6_info")
Reported-by: Brian Rak <brak@choopa.com>
Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Ahern 2020-07-06 11:45:07 -06:00 committed by David S. Miller
parent eadede5f93
commit 34fe5a1cf9
2 changed files with 17 additions and 1 deletions
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5
net/ipv6/route.c
View File

@ -431,9 +431,12 @@ void fib6_select_path(const struct net *net, struct fib6_result *res,
struct fib6_info *sibling, *next_sibling;
struct fib6_info *match = res->f6i;
if ((!match->fib6_nsiblings && !match->nh) || have_oif_match)
if (!match->nh && (!match->fib6_nsiblings || have_oif_match))
goto out;
if (match->nh && have_oif_match && res->nh)
return;
/* We might have already computed the hash for ICMPv6 errors. In such
* case it will always be non-zero. Otherwise now is the time to do it.
*/

13
tools/testing/selftests/net/fib_nexthops.sh
View File

@ -747,6 +747,19 @@ ipv6_fcnal_runtime()
run_cmd "$IP nexthop add id 86 via 2001:db8:91::2 dev veth1"
run_cmd "$IP ro add 2001:db8:101::1/128 nhid 81"
# rpfilter and default route
$IP nexthop flush >/dev/null 2>&1
run_cmd "ip netns exec me ip6tables -t mangle -I PREROUTING 1 -m rpfilter --invert -j DROP"
run_cmd "$IP nexthop add id 91 via 2001:db8:91::2 dev veth1"
run_cmd "$IP nexthop add id 92 via 2001:db8:92::2 dev veth3"
run_cmd "$IP nexthop add id 93 group 91/92"
run_cmd "$IP -6 ro add default nhid 91"
run_cmd "ip netns exec me ping -c1 -w1 2001:db8:101::1"
log_test $? 0 "Nexthop with default route and rpfilter"
run_cmd "$IP -6 ro replace default nhid 93"
run_cmd "ip netns exec me ping -c1 -w1 2001:db8:101::1"
log_test $? 0 "Nexthop with multipath default route and rpfilter"
# TO-DO:
# existing route with old nexthop; append route with new nexthop
# existing route with old nexthop; replace route with new