From 8743aeff5bc4dcb5b87b43765f48d5ac3ad7dd9f Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Tue, 8 Aug 2023 10:52:33 +0300 Subject: [PATCH] nexthop: Fix infinite nexthop bucket 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 bucket dump callback always returns a positive number if nexthop buckets 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 nexthop buckets are present. In the last recvmsg() call the dump callback will not fill in any nexthop buckets because the previous call indicated that the dump should restart from the last dumped nexthop ID plus one. # ip link add name dummy1 up type dummy # ip nexthop add id 1 dev dummy1 # ip nexthop add id 10 group 1 type resilient buckets 2 # strace -e sendto,recvmsg -s 5 ip nexthop bucket sendto(3, [[{nlmsg_len=24, nlmsg_type=RTM_GETNEXTHOPBUCKET, nlmsg_flags=NLM_F_REQUEST|NLM_F_DUMP, nlmsg_seq=1691396980, nlmsg_pid=0}, {family=AF_UNSPEC, data="\x00\x00\x00\x00\x00"...}], {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) = 128 recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[[{nlmsg_len=64, nlmsg_type=RTM_NEWNEXTHOPBUCKET, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691396980, nlmsg_pid=347}, {family=AF_UNSPEC, data="\x00\x00\x00\x00\x00"...}], [{nlmsg_len=64, nlmsg_type=RTM_NEWNEXTHOPBUCKET, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691396980, nlmsg_pid=347}, {family=AF_UNSPEC, data="\x00\x00\x00\x00\x00"...}]], iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 128 id 10 index 0 idle_time 6.66 nhid 1 id 10 index 1 idle_time 6.66 nhid 1 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=1691396980, nlmsg_pid=347}, 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 link add name dummy1 up type dummy # ip nexthop add id 1 dev dummy1 # ip nexthop add id $((2**32-1)) group 1 type resilient buckets 2 # ip nexthop bucket id 4294967295 index 0 idle_time 5.55 nhid 1 id 4294967295 index 1 idle_time 5.55 nhid 1 id 4294967295 index 0 idle_time 5.55 nhid 1 id 4294967295 index 1 idle_time 5.55 nhid 1 [...] 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_NEWNEXTHOPBUCKET responses: # ip link add name dummy1 up type dummy # ip nexthop add id 1 dev dummy1 # ip nexthop add id $((2**32-1)) group 1 type resilient buckets 2 # strace -e sendto,recvmsg -s 5 ip nexthop bucket sendto(3, [[{nlmsg_len=24, nlmsg_type=RTM_GETNEXTHOPBUCKET, nlmsg_flags=NLM_F_REQUEST|NLM_F_DUMP, nlmsg_seq=1691396737, nlmsg_pid=0}, {family=AF_UNSPEC, data="\x00\x00\x00\x00\x00"...}], {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) = 148 recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[[{nlmsg_len=64, nlmsg_type=RTM_NEWNEXTHOPBUCKET, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691396737, nlmsg_pid=350}, {family=AF_UNSPEC, data="\x00\x00\x00\x00\x00"...}], [{nlmsg_len=64, nlmsg_type=RTM_NEWNEXTHOPBUCKET, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691396737, nlmsg_pid=350}, {family=AF_UNSPEC, data="\x00\x00\x00\x00\x00"...}], [{nlmsg_len=20, nlmsg_type=NLMSG_DONE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1691396737, nlmsg_pid=350}, 0]], iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 148 id 4294967295 index 0 idle_time 6.61 nhid 1 id 4294967295 index 1 idle_time 6.61 nhid 1 +++ 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_res [...] TEST: Maximum nexthop ID dump [FAIL] [...] And passes after it: # ./fib_nexthops.sh -t basic_res [...] TEST: Maximum nexthop ID dump [ OK ] [...] Fixes: 8a1bbabb034d ("nexthop: Add netlink handlers for bucket dump") Signed-off-by: Ido Schimmel Reviewed-by: Petr Machata Reviewed-by: David Ahern Link: https://lore.kernel.org/r/20230808075233.3337922-4-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 f365a4f63899..be5498f5dd31 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -3424,13 +3424,9 @@ static int rtm_dump_nexthop_bucket(struct sk_buff *skb, 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 10aa059b9f06..df8d90b51867 100755 --- a/tools/testing/selftests/net/fib_nexthops.sh +++ b/tools/testing/selftests/net/fib_nexthops.sh @@ -2206,6 +2206,11 @@ basic_res() run_cmd "$IP nexthop bucket list fdb" log_test $? 255 "Dump all nexthop buckets with invalid 'fdb' keyword" + # Dump should not loop endlessly when maximum nexthop ID is configured. + run_cmd "$IP nexthop add id $((2**32-1)) group 1/2 type resilient buckets 4" + run_cmd "timeout 5 $IP nexthop bucket" + log_test $? 0 "Maximum nexthop ID dump" + # # resilient nexthop buckets get requests #