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Opened 3 years ago

Last modified 18 months ago

#18404 new defect

sysntpd uses the wrong source address

Reported by: jch@… Owned by: developers
Priority: normal Milestone:
Component: base system Version: Barrier Breaker 14.07
Keywords: busybox ntp Cc:

Description

Sysntpd doesn't use the destination address of the request as the source address, it defers to the kernel to choose one. This is incorrect with multiple interfaces.

20:35:04.727958 IP 192.168.3.198.37306 > 192.168.1.1.123: NTPv3, Client, length 48
20:35:04.728275 IP 192.168.3.1.123 > 192.168.3.198.37306: NTPv3, Server, length 48

Here, 192.168.1.1 is the address advertised in DNS. The NTP client sends a request to that address, but sysntpd replies from the address 192.168.3.1 (the address assigned to the link on which the request came). The client, correctly enough, discards the reply.

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Change History (2)

comment:1 Changed 3 years ago by jch@…

I've checked the source, and there's nothing obviously wrong -- it uses the right auxiliary data, and would appear to do the right thing.

The issue is also not due to some strange SNATing, since it persists even if the firewall is disabled.

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