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Message-ID: <20220217155351.GR7074@brightrain.aerifal.cx>
Date: Thu, 17 Feb 2022 10:53:52 -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 09:49:45AM -0500, Satadru Pramanik wrote:
> Apologies for not being as familiar with gdb as I ought to be.
> I used the __clock_gettime64 breakpoint and did a backtrace and finish
> repeatedly.
> I couldn't figure out how to best get the timespec struct info.
>
> Alternately if you want to throw out a sample test program for me to build
> and run, and what gdb commands to run to get the right info, happy to do
> that too.
>
> gdb output is attached.
If gdb reported it correctly, clock_gettime returned 403, which should
be impossible. It can only return 0 or -1. Incidentally, 403 is the
syscall number for SYS_clock_gettime64, which suggests your kernel is
simply *returning the syscall number* instead of -ENOSYS for syscalls
that don't exist on it. Is this a stock kernel (3.8 IIRC) or does it
have any sort of weird vendor patching? Any LSMs loaded?
If you'd like to run a test just to make sure we're accurately seeing
what's happening, the attached should work. It should print 0 followed
by the current time in seconds and nanoseconds.
> On Thu, Feb 17, 2022 at 8:46 AM Rich Felker <dalias@...ifal.cx> wrote:
>
> > 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
> >
View attachment "cgt.c" of type "text/plain" (185 bytes)
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