Re: [musl] Re: musl getaddr info breakage on older kernels

[Satadru Pramanik <satadru@gmail.com>]

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I'm noticing one small issue with this suggested patch:

In file included from ../src_musl/src/internal/syscall.h:6,
                 from ../src_musl/src/dirent/opendir.c:6:
../src_musl/arch/i386/syscall_arch.h: In function ‘__syscall0’:
../src_musl/arch/i386/syscall_arch.h:17:28: error: ‘ENOSYS’ undeclared
(first use in this function)
   17 |         if (n>350) return -ENOSYS;
      |                            ^~~~~~
../src_musl/arch/i386/syscall_arch.h:17:28: note: each undeclared
identifier is reported only once for each function it appears in
../src_musl/arch/i386/syscall_arch.h: In function ‘__syscall1’:
../src_musl/arch/i386/syscall_arch.h:25:28: error: ‘ENOSYS’ undeclared
(first use in this function)
   25 |         if (n>350) return -ENOSYS;
      |                            ^~~~~~
../src_musl/arch/i386/syscall_arch.h: In function ‘__syscall2’:
../src_musl/arch/i386/syscall_arch.h:33:28: error: ‘ENOSYS’ undeclared
(first use in this function)
   33 |         if (n>350) return -ENOSYS;

Should we be adding an include or just defining this locally?

Satadru

On Thu, Feb 17, 2022 at 1:17 PM Rich Felker <dalias@aerifal.cx> wrote:

> On Thu, Feb 17, 2022 at 11:36:31AM -0500, Satadru Pramanik wrote:
> >  This machine is a EOL Samsung Series 5 Chromebook
> > <
> https://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices/samsung-series-5-chromebook/
> >
> > code
> > named Alex
> > <
> https://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices/#:~:text=Series%205%20Chromebook-,Alex,-x86%2Dalex%20%26%20x86
> >
> > ..
> > It is the target device for our i686 builds for Chromebrew.
> >
> > It is running a 3.8.11 kernel, and I believe the kernel source for that
> is
> > here:
> >
> https://chromium.googlesource.com/chromiumos/third_party/kernel/+/refs/heads/chromeos-3.8
> >
> > Getting a signed kernel update for an EOL kernel for an EOL machine is
> > close to impossible from Google, so we're just trying to work around
> these
>
> If these are machines you're in control of, you may be able to load a
> module to patch it. If this is something you're deploying to users
> stuck on that kernel who don't want to fix their systems, then of
> course that's not a practical option.
>
> > issues in userspace to maintain some functionality for any users who may
> > still be using the device.
> >
> > The simplest workaround possible would be ideal.
>
> If you're shipping binaries specifically for these devices, the
> simplest fix is just to emulate the failure that should happen in the
> kernel in userspace, using the attached patch. DO NOT deploy this
> patch in binaries meant to be used on modern systems, since they will
> break when Y2038 rolls around. (Your old Chromebooks will break then
> too.)
>
> > It is interesting though
> > that the sample program works fine when built against near-stock glibc
> > 2.23, no?
>
> No. If your kernel has a bug that makes something behave wildly wrong,
> whether you do or don't see that as visible breakage with a particular
> piece of software is not particularly interesting.
>
> I'm pretty sure, however, that you just haven't tested enough to see
> any failures. glibc 2.23 is from 2016, so any functionality in it
> using syscalls added after 2011 (3.8 kernel) is going to blow up
> badly, thinking the syscall succeeded and returned some positive value
> when actually the kernel lacks it.
>
> In the particular case of clock_gettime, it's just that your glibc
> 2.23 has a hard Y2038 EOL and does not use/support the missing time64
> syscalls.
>
>
> > On Thu, Feb 17, 2022 at 11:05 AM Rich Felker <dalias@aerifal.cx> wrote:
> >
> > > On Thu, Feb 17, 2022 at 10:53:52AM -0500, Rich Felker wrote:
> > > > 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.
> > >
> > > It looks like you hit the bug introduced in commit
> > > 554086d85e71f30abe46fc014fea31929a7c6a8a and fixed in commit
> > > 8142b215501f8b291a108a202b3a053a265b03dd. It looks like, since the
> > > former was a CVE fix, somebody backported it to the kernel you're
> > > using, but they failed to backport the fix-for-the-fix, so you have a
> > > kernel that operates dangerously incorrectly for syscall numbers it's
> > > unaware of.
> > >
> > > This really needs to be fixed in the kernel if you can. On our side
> > > (musl) we probably need to find out if such kernels are actually out
> > > in the wild, and if so, whether there's any reasonable way to detect
> > > the false success and treat it as failure.
> > >
> > > > > On Thu, Feb 17, 2022 at 8:46 AM Rich Felker <dalias@aerifal.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
> > > > > >
> > > >
> > > >
> > >
> > > > #include <time.h>
> > > > #include <stdio.h>
> > > > int main()
> > > > {
> > > >       struct timespec ts;
> > > >       printf("%d", clock_gettime(CLOCK_REALTIME, &ts));
> > > >       printf(" %lld %.9ld\n", (long long)ts.tv_sec, ts.tv_nsec);
> > > > }
> > >
> > >
>

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