Messages in this thread Patch in this message | | | From | Ziyang Xuan <> | Subject | [PATCH net] ipv4: fix source address and gateway mismatch under multiple default gateways | Date | Wed, 26 Oct 2022 11:20:17 +0800 |
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We found a problem that source address doesn't match with selected gateway under multiple default gateways. The reproducer is as following:
Setup in client as following:
$ ip link add link eth2 dev eth2.71 type vlan id 71 $ ip link add link eth2 dev eth2.72 type vlan id 72 $ ip addr add 192.168.71.41/24 dev eth2.71 $ ip addr add 192.168.72.41/24 dev eth2.72 $ ip link set eth2.71 up $ ip link set eth2.72 up $ route add -net default gw 192.168.71.1 dev eth2.71 $ route add -net default gw 192.168.72.1 dev eth2.72
Add a nameserver configuration in the following file: $ cat /etc/resolv.conf nameserver 8.8.8.8
Setup in peer server as following:
$ ip link add link eth2 dev eth2.71 type vlan id 71 $ ip link add link eth2 dev eth2.72 type vlan id 72 $ ip addr add 192.168.71.1/24 dev eth2.71 $ ip addr add 192.168.72.1/24 dev eth2.72 $ ip link set eth2.71 up $ ip link set eth2.72 up
Use the following command trigger DNS packet in client: $ ping www.baidu.com
Capture packets with tcpdump in client when ping: $ tcpdump -i eth2 -vne ... 20:30:22.996044 52:54:00:20:23:a9 > 52:54:00:d2:4f:e3, ethertype 802.1Q (0x8100), length 77: vlan 71, p 0, ethertype IPv4, (tos 0x0, ttl 64, id 25407, offset 0, flags [DF], proto UDP (17), length 59) 192.168.72.41.42666 > 8.8.8.8.domain: 58562+ A? www.baidu.com. (31) ...
We get the problem that IPv4 saddr "192.168.72.41" do not match with selected VLAN device "eth2.71".
In above scenario, the process does __ip_route_output_key() twice in ip_route_connect(), the two processes have chosen different default gateway, and the last choice is not the best.
Add flowi4->saddr and fib_nh_common->nhc_gw.ipv4 matching consideration in fib_select_default() to fix that.
Fixes: 19baf839ff4a ("[IPV4]: Add LC-Trie FIB lookup algorithm.") Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com> --- net/ipv4/fib_semantics.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index e9a7f70a54df..8bd94875a009 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -2046,6 +2046,7 @@ static void fib_select_default(const struct flowi4 *flp, struct fib_result *res) int order = -1, last_idx = -1; struct fib_alias *fa, *fa1 = NULL; u32 last_prio = res->fi->fib_priority; + u8 prefix, max_prefix = 0; dscp_t last_dscp = 0; hlist_for_each_entry_rcu(fa, fa_head, fa_list) { @@ -2078,6 +2079,11 @@ static void fib_select_default(const struct flowi4 *flp, struct fib_result *res) if (!nhc->nhc_gw_family || nhc->nhc_scope != RT_SCOPE_LINK) continue; + prefix = __ffs(flp->saddr ^ nhc->nhc_gw.ipv4); + if (prefix < max_prefix) + continue; + max_prefix = max_t(u8, prefix, max_prefix); + fib_alias_accessed(fa); if (!fi) { -- 2.25.1
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