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udhcp: bind to device even for ucast packets

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There are cases where binding to source IP and
destination IP is insufficient to guarantee sane
xmit netdev.

One case where this can fail is when
route-matching netdev carrier is down (cable
unplugged, wifi disconnected), or the netdev is
admin down. Then all the IP based bindings (bind()
+ connect()) will seemingly succeed but the actual
packet can go out through a default gw path.

Depending on the network this happens on
it can create issues or false alarms. It can
also leak some subnet info across networks that
shouldn't be routed.

As such better be safe than sorry and bind to a
netdev to be sure it's used for xmit.

function                                             old     new   delta
udhcp_send_kernel_packet                             293     336     +43
send_packet                                          182     188      +6
bcast_or_ucast                                        37      43      +6
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 55/0)               Total: 55 bytes

Signed-off-by: Michal Kazior <michal@plume.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Michal Kazior
2020-12-15 09:53:40 +00:00
committed by Denys Vlasenko
parent 01004f9796
commit b817699e6c
4 changed files with 23 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
networking/udhcp/dhcpc.c
View File

@ -702,7 +702,8 @@ static int bcast_or_ucast(struct dhcp_packet *packet, uint32_t ciaddr, uint32_t
if (server)
return udhcp_send_kernel_packet(packet,
ciaddr, CLIENT_PORT,
server, SERVER_PORT);
server, SERVER_PORT,
client_data.interface);
return raw_bcast_from_client_data_ifindex(packet, ciaddr);
}