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Date: Thu, 17 Feb 2022 08:46:51 -0500
From: Rich Felker <dalias@...ifal.cx>
To: Satadru Pramanik <satadru@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: Re: musl getaddr info breakage on older kernels
On Thu, Feb 17, 2022 at 08:30:47AM -0500, Satadru Pramanik wrote:
> *This is a failure:*
> tcpdump -i any -vvv host 192.168.0.115
> tcpdump: listening on any, link-type LINUX_SLL (Linux cooked v1), capture
> size 262144 bytes
> 08:29:38.043849 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP
> (17), length 56)
> 192.168.0.115.60625 > office.lan.53: [udp sum ok] 0+ A? google.com. (28)
> 08:29:38.044237 IP (tos 0x0, ttl 64, id 11463, offset 0, flags [DF], proto
> UDP (17), length 72)
> office.lan.53 > 192.168.0.115.60625: [bad udp cksum 0x820a -> 0x5c7d!]
> 0 q: A? google.com. 1/0/0 google.com. [2m15s] A 142.250.80.110 (44)
> 08:29:38.047754 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP
> (17), length 56)
> 192.168.0.115.60625 > office.lan.53: [udp sum ok] 0+ AAAA? google.com.
> (28)
> 08:29:38.048078 IP (tos 0x0, ttl 64, id 11464, offset 0, flags [DF], proto
> UDP (17), length 84)
> office.lan.53 > 192.168.0.115.60625: [bad udp cksum 0x8216 -> 0xb42f!]
> 0 q: AAAA? google.com. 1/0/0 google.com. [4m26s] AAAA
> 2607:f8b0:4006:80d::200e (56)
> 08:29:38.048955 IP (tos 0xc0, ttl 64, id 59728, offset 0, flags [none],
> proto ICMP (1), length 112)
> 192.168.0.115 > office.lan: ICMP 192.168.0.115 udp port 60625
> unreachable, length 92
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OK, this shows that the client has requested both answers and the
nameserver replied almost immediately (about 0.5ms later), but when
the second reply arrives (to the AAAA), the client has already closed
the listening port, despite only a few ms having passed. The only way
I see this could happen is by "timing out". This suggests that
something is wrong with telling time.
Can you either put a breakpoint in __clock_gettime64 (this is the name
you have to use for a breakpoint -- sorry I messed it up last time)
and then see what it returns when you "finish" it and what's in the
timespec struct after that? Or just write a test program to call
clock_gettime(CLOCK_REALTIME, &ts) (note: you do NOT need or want to
use the time64 symbol name here) and print the results (return value
and contents of the timespec struct).
> IP (tos 0x0, ttl 64, id 11464, offset 0, flags [DF], proto UDP
> (17), length 84)
> office.lan.53 > 192.168.0.115.60625: [udp sum ok] 0 q: AAAA? google.com.
> 1/0/0 google.com. [4m26s] AAAA 2607:f8b0:4006:80d::200e (56)
> 08:29:39.476101 IP (tos 0x0, ttl 64, id 12690, offset 0, flags [DF], proto
> TCP (6), length 52)
> 192.168.0.115.51204 > lga34s35-in-f3.1e100.net.80: Flags [.], cksum
> 0xa666 (correct), seq 1466707759, ack 3358943837, win 115, options
> [nop,nop,TS val 198422160 ecr 2351261566], length 0
> 08:29:39.478914 IP (tos 0x80, ttl 122, id 6227, offset 0, flags [none],
> proto TCP (6), length 52)
> lga34s35-in-f3.1e100.net.80 > 192.168.0.115.51204: Flags [.], cksum
> 0xa5b7 (correct), seq 1, ack 1, win 282, options [nop,nop,TS val 2351306585
> ecr 198377148], length 0
> ^C
> 7 packets captured
> 7 packets received by filter
> 0 packets dropped by kernel
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