From 913f60cacda73ccac8eead94983e5884c03e04cd Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Tue, 8 Aug 2023 10:52:31 +0300 Subject: [PATCH] nexthop: Fix infinite nexthop dump when using maximum nexthop ID A netlink dump callback can return a positive number to signal that more information needs to be dumped or zero to signal that the dump is complete. In the second case, the core netlink code will append the NLMSG_DONE message to the skb in order to indicate to user space that the dump is complete. The nexthop dump callback always returns a positive number if nexthops were filled in the provided skb, even if the dump is complete. This means that a dump will span at least two recvmsg() calls as long as nexthops are present. In the last recvmsg() call the dump callback will not fill in any nexthops because the previous call indicated that the dump should restart from the last dumped nexthop ID plus one. # ip nexthop add id 1 blackhole # strace -e sendto,recvmsg -s 5 ip nexthop sendto(3, [[{nlmsg_len=24, nlmsg_type=RTM_GETNEXTHOP, nlmsg_flags=NLM_F_REQUEST|NLM_F_DUMP, nlmsg_seq=1691394315, nlmsg_pid=0}, {nh_family=AF_UNSPEC, nh_scope=RT_SCOPE_UNIVERSE, nh_protocol=RTPROT_UNSPEC, nh_flags=0}], {nlmsg_len=0, nlmsg_type=0 /* NLMSG_??? */, nlmsg_flags=0, nlmsg_seq=0, nlmsg_pid=0}], 152, 0, NULL, 0) = 152 recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=NULL, iov_len=0}], msg_iovlen=1, msg_controllen=0, msg_flags=MSG_TRUNC}, MSG_PEEK|MSG_TRUNC) = 36 recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[{nlmsg_len=36, nlmsg_type=RTM_NEWNEXTHOP, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691394315, nlmsg_pid=343}, {nh_family=AF_INET, nh_scope=RT_SCOPE_UNIVERSE, nh_protocol=RTPROT_UNSPEC, nh_flags=0}, [[{nla_len=8, nla_type=NHA_ID}, 1], {nla_len=4, nla_type=NHA_BLACKHOLE}]], iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 36 id 1 blackhole recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=NULL, iov_len=0}], msg_iovlen=1, msg_controllen=0, msg_flags=MSG_TRUNC}, MSG_PEEK|MSG_TRUNC) = 20 recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[{nlmsg_len=20, nlmsg_type=NLMSG_DONE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691394315, nlmsg_pid=343}, 0], iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 20 +++ exited with 0 +++ This behavior is both inefficient and buggy. If the last nexthop to be dumped had the maximum ID of 0xffffffff, then the dump will restart from 0 (0xffffffff + 1) and never end: # ip nexthop add id $((2**32-1)) blackhole # ip nexthop id 4294967295 blackhole id 4294967295 blackhole [...] Fix by adjusting the dump callback to return zero when the dump is complete. After the fix only one recvmsg() call is made and the NLMSG_DONE message is appended to the RTM_NEWNEXTHOP response: # ip nexthop add id $((2**32-1)) blackhole # strace -e sendto,recvmsg -s 5 ip nexthop sendto(3, [[{nlmsg_len=24, nlmsg_type=RTM_GETNEXTHOP, nlmsg_flags=NLM_F_REQUEST|NLM_F_DUMP, nlmsg_seq=1691394080, nlmsg_pid=0}, {nh_family=AF_UNSPEC, nh_scope=RT_SCOPE_UNIVERSE, nh_protocol=RTPROT_UNSPEC, nh_flags=0}], {nlmsg_len=0, nlmsg_type=0 /* NLMSG_??? */, nlmsg_flags=0, nlmsg_seq=0, nlmsg_pid=0}], 152, 0, NULL, 0) = 152 recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=NULL, iov_len=0}], msg_iovlen=1, msg_controllen=0, msg_flags=MSG_TRUNC}, MSG_PEEK|MSG_TRUNC) = 56 recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[[{nlmsg_len=36, nlmsg_type=RTM_NEWNEXTHOP, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691394080, nlmsg_pid=342}, {nh_family=AF_INET, nh_scope=RT_SCOPE_UNIVERSE, nh_protocol=RTPROT_UNSPEC, nh_flags=0}, [[{nla_len=8, nla_type=NHA_ID}, 4294967295], {nla_len=4, nla_type=NHA_BLACKHOLE}]], [{nlmsg_len=20, nlmsg_type=NLMSG_DONE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691394080, nlmsg_pid=342}, 0]], iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 56 id 4294967295 blackhole +++ exited with 0 +++ Note that if the NLMSG_DONE message cannot be appended because of size limitations, then another recvmsg() will be needed, but the core netlink code will not invoke the dump callback and simply reply with a NLMSG_DONE message since it knows that the callback previously returned zero. Add a test that fails before the fix: # ./fib_nexthops.sh -t basic [...] TEST: Maximum nexthop ID dump [FAIL] [...] And passes after it: # ./fib_nexthops.sh -t basic [...] TEST: Maximum nexthop ID dump [ OK ] [...] Fixes: ab84be7e54fc ("net: Initial nexthop code") Reported-by: Petr Machata Closes: https://lore.kernel.org/netdev/87sf91enuf.fsf@nvidia.com/ Signed-off-by: Ido Schimmel Reviewed-by: Petr Machata Reviewed-by: David Ahern Link: https://lore.kernel.org/r/20230808075233.3337922-2-idosch@nvidia.com Signed-off-by: Jakub Kicinski --- net/ipv4/nexthop.c | 6 +----- tools/testing/selftests/net/fib_nexthops.sh | 5 +++++ 2 files changed, 6 insertions(+), 5 deletions(-) diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c index f95142e..179e50d 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -3221,13 +3221,9 @@ static int rtm_dump_nexthop(struct sk_buff *skb, struct netlink_callback *cb) &rtm_dump_nexthop_cb, &filter); if (err < 0) { if (likely(skb->len)) - goto out; - goto out_err; + err = skb->len; } -out: - err = skb->len; -out_err: cb->seq = net->nexthop.seq; nl_dump_check_consistent(cb, nlmsg_hdr(skb)); return err; diff --git a/tools/testing/selftests/net/fib_nexthops.sh b/tools/testing/selftests/net/fib_nexthops.sh index 0f5e88c..10aa059 100755 --- a/tools/testing/selftests/net/fib_nexthops.sh +++ b/tools/testing/selftests/net/fib_nexthops.sh @@ -1981,6 +1981,11 @@ basic() run_cmd "$IP link set dev lo up" + # Dump should not loop endlessly when maximum nexthop ID is configured. + run_cmd "$IP nexthop add id $((2**32-1)) blackhole" + run_cmd "timeout 5 $IP nexthop" + log_test $? 0 "Maximum nexthop ID dump" + # # groups # -- 2.7.4