Re: Regression in unix stream sockets with the Smack LSM

From: Casey Schaufler
Date: Mon Sep 20 2021 - 19:46:44 EST

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In reply to: Jiang Wang .: "Re: Re: Regression in unix stream sockets with the Smack LSM"
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On 9/20/2021 3:35 PM, Jiang Wang . wrote:
> On Wed, Sep 15, 2021 at 9:52 AM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>> On 9/13/2021 4:47 PM, Paul Moore wrote:
>>> On Mon, Sep 13, 2021 at 6:53 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>>>> Commit 77462de14a43f4d98dbd8de0f5743a4e02450b1d
>>>>
>>>> af_unix: Add read_sock for stream socket types
>>>>
>>>> introduced a regression in UDS socket connections for the Smack LSM.
>>>> I have not tracked done the details of why the change broke the code,
>>>> but this is where bisecting the kernel indicates the problem lies, and
>>>> I have verified that reverting this change repairs the problem.
>>>>
>>>> You can verify the problem with the Smack test suite:
>>>>
>>>> https://github.com/smack-team/smack-testsuite.git
>>>>
>>>> The failing test is tests/uds-access.sh.
>>>>
> I tried to reproduce with tests/uds-access.sh, but the first two test
> cases always failed.

That was my initial impression as well. However, when I started
running the tests outside the routine "make test-results" I started
observing that they succeeded irregularly.

My biggest concern is that the test ever fails. The uds-access test
has not failed in several releases. The erratic behavior just adds
spice to the problem.

> I tried different kernels with and without my
> unix-stream sockmap patches. Also tried standard debian 4.19
> kernel and they all have the same result. What distro did you use? centos?
> Fedora?

I have been testing on Fedora32 and Fedora34.

> Have you tested on debian based distros?

Ubuntu 20.04.3 with a 5.15-rc1 kernel is exhibiting the same
behavior. The Ubuntu system fails the test more regularly, but
does succeed on occasion.

> failing log:
> root@gitlab-runner-stretch:~/smack-testsuite# tests/uds-access.sh -v

# tools/clean-targets.sh
# tests/uds-access.sh -v

will remove the UDS filesystem entry before the test runs.

> mkdir: cannot create directory ‘./targets/uds-notroot’: File exists
> tests/uds-access.sh:71 FAIL
> tests/uds-access.sh:76 FAIL
> tests/uds-access.sh:81 PASS
> tests/uds-access.sh:86 PASS
> tests/uds-access.sh:91 PASS
> tests/uds-access.sh PASS=3 FAIL=2
> root@gitlab-runner-stretch:~/smack-testsuite# uname -a
> Linux gitlab-runner-stretch 5.14.0-rc5.bm.1-amd64+ #6 SMP Mon Sep 20
> 22:01:10 UTC 2021 x86_64 GNU/Linux
> root@gitlab-runner-stretch:~/smack-testsuite#
>
>>>> I have not looked to see if there's a similar problem with SELinux.
>>>> There may be, but if there isn't it doesn't matter, there's still a
>>>> bug.
>>> FWIW, the selinux-testsuite tests ran clean today with v5.15-rc1 (it
>>> looks like this code is only in v5.15) but as Casey said, a regression
>>> is a regression.
>>>
>>> Casey, what actually fails on the Smack system with this commit?
>> This problem occurs with security=none as well as with security=smack.
>>
>> There isn't a problem with connect, that always works correctly.
>> The problem is an unexpected read() failure in the connecting process.
>> This doesn't occur all the time, and sometimes happens in the first
>> of my two tests, sometimes the second, sometimes neither and, you guessed
>> it, sometimes both.
>>
>> Here's a sample socat log demonstrating the problem. The first run,
>> ending at "uds-access RC=0" behaves as expected. The second, ending
>> at "uds-access RC=1", demonstrates the read failure. This case was
> I tried to compare logs between RC=0 and RC=1, but they look to me
> not apple to apple comparison? The read syscall have different parameters
> and the syscall sequences are different. I am not sure which syscall
> is the first failure. See more comments below.

The data being feed to socat is the Smack label, so the data passed across
the socket will be of different length ("Pop" vs. "Snap") between the
two test cases, but that should be the only difference.

>> run with Smack enabled, but I see the same problem with the same
>> unpredictability on the same kernel with security=none.
>>
>> I've tried to convince myself that there's a flaw in the way I've
>> set up the scripts. They've been pretty robust and I've never seen
>> socat behaving erratically before. I've instrumented the kernel
>> code and all the security checks are behaving as expected. Plus,
>> as I mentioned above, the problem also occurs without an LSM.
>>
>> 2021/09/15 08:49:50 socat[2215] D getpid()
>> 2021/09/15 08:49:50 socat[2215] D getpid() -> 2215
>> 2021/09/15 08:49:50 socat[2215] D setenv("SOCAT_PID", "2215", 1)
>> 2021/09/15 08:49:50 socat[2215] D setenv() -> 0
>> 2021/09/15 08:49:50 socat[2215] D setenv("SOCAT_PPID", "2215", 1)
>> 2021/09/15 08:49:50 socat[2215] D setenv() -> 0
>> 2021/09/15 08:49:50 socat[2215] I socat by Gerhard Rieger and contributors - see www.dest-unreach.org
>> 2021/09/15 08:49:50 socat[2215] I This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. (http://www.openssl.org/)
>> 2021/09/15 08:49:50 socat[2215] I This product includes software written by Tim Hudson (tjh@xxxxxxxxxxxxx)
>> 2021/09/15 08:49:50 socat[2215] D socat version 1.7.4.1 on Jan 27 2021 00:00:00
>> 2021/09/15 08:49:50 socat[2215] D setenv("SOCAT_VERSION", "1.7.4.1", 1)
>> 2021/09/15 08:49:50 socat[2215] D setenv() -> 0
>> 2021/09/15 08:49:50 socat[2215] D running on Linux version #58 SMP Wed Sep 15 08:40:38 PDT 2021, release 5.15.0-rc1bisect, machine x86_64
>>
>> 2021/09/15 08:49:50 socat[2215] D argv[0]: "socat"
>> 2021/09/15 08:49:50 socat[2215] D argv[1]: "-d"
>> 2021/09/15 08:49:50 socat[2215] D argv[2]: "-d"
>> 2021/09/15 08:49:50 socat[2215] D argv[3]: "-d"
>> 2021/09/15 08:49:50 socat[2215] D argv[4]: "-d"
>> 2021/09/15 08:49:50 socat[2215] D argv[5]: "-"
>> 2021/09/15 08:49:50 socat[2215] D argv[6]: "UNIX-CONNECT:./targets/uds-notroot/uds-access-socket"
>> 2021/09/15 08:49:50 socat[2215] D sigaction(1, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(2, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(3, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(4, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(6, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(7, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(8, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(11, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D sigaction(15, 0x7fffaec50b50, 0x0)
>> 2021/09/15 08:49:50 socat[2215] D sigaction() -> 0
>> 2021/09/15 08:49:50 socat[2215] D signal(13, 0x1)
>> 2021/09/15 08:49:50 socat[2215] D signal() -> 0x0
>> 2021/09/15 08:49:50 socat[2215] D atexit(0x55aa5d645110)
>> 2021/09/15 08:49:50 socat[2215] D atexit() -> 0
>> 2021/09/15 08:49:50 socat[2215] D xioopen("-")
>> 2021/09/15 08:49:50 socat[2215] D calloc(1, 824)
>> 2021/09/15 08:49:50 socat[2215] D calloc() -> 0x55aa5f0139d0
>> 2021/09/15 08:49:50 socat[2215] D malloc(1024)
>> 2021/09/15 08:49:50 socat[2215] D malloc() -> 0x55aa5f013d30
>> 2021/09/15 08:49:50 socat[2215] D calloc(1, 824)
>> 2021/09/15 08:49:50 socat[2215] D calloc() -> 0x55aa5f014140
>> 2021/09/15 08:49:50 socat[2215] D calloc(1, 824)
>> 2021/09/15 08:49:50 socat[2215] D calloc() -> 0x55aa5f014bc0
>> 2021/09/15 08:49:50 socat[2215] D isatty(0)
>> 2021/09/15 08:49:50 socat[2215] D isatty() -> 0
>> 2021/09/15 08:49:50 socat[2215] D isatty(1)
>> 2021/09/15 08:49:50 socat[2215] D isatty() -> 0
>> 2021/09/15 08:49:50 socat[2215] D malloc(128)
>> 2021/09/15 08:49:50 socat[2215] D malloc() -> 0x55aa5f014f00
>> 2021/09/15 08:49:50 socat[2215] D malloc(128)
>> 2021/09/15 08:49:50 socat[2215] D malloc() -> 0x55aa5f014f90
>> 2021/09/15 08:49:50 socat[2215] N reading from and writing to stdio
>> 2021/09/15 08:49:50 socat[2215] D xioopen("UNIX-CONNECT:./targets/uds-notroot/uds-access-socket")
>> 2021/09/15 08:49:50 socat[2215] D calloc(1, 824)
>> 2021/09/15 08:49:50 socat[2215] D calloc() -> 0x55aa5f015020
>> 2021/09/15 08:49:50 socat[2215] D malloc(1024)
>> 2021/09/15 08:49:50 socat[2215] D malloc() -> 0x55aa5f015360
>> 2021/09/15 08:49:50 socat[2215] D malloc(128)
>> 2021/09/15 08:49:50 socat[2215] D malloc() -> 0x55aa5f015770
>> 2021/09/15 08:49:50 socat[2215] N opening connection to AF=1 "./targets/uds-notroot/uds-access-socket"
>> 2021/09/15 08:49:50 socat[2215] D socket(1, 1, 0)
>> 2021/09/15 08:49:50 socat[2215] I socket(1, 1, 0) -> 5
>> 2021/09/15 08:49:50 socat[2215] D fcntl(5, 2, 1)
>> 2021/09/15 08:49:50 socat[2215] D fcntl() -> 0
>> 2021/09/15 08:49:50 socat[2215] D connect(5, {1,AF=1 "./targets/uds-notroot/uds-access-socket"}, 41)
>> 2021/09/15 08:49:50 socat[2215] D connect() -> 0
>> 2021/09/15 08:49:50 socat[2215] D getsockname(5, 0x7fffaec50580, 0x7fffaec50564{112})
>> 2021/09/15 08:49:50 socat[2215] D getsockname(, {AF=1 "<anon>"}, {2}) -> 0
>> 2021/09/15 08:49:50 socat[2215] N successfully connected from local address AF=1 "uds-notroot/ud\xEE\xEE\xEE\xEEcess-socket")\n"
>> 2021/09/15 08:49:50 socat[2215] I resolved and opened all sock addresses
>> 2021/09/15 08:49:50 socat[2215] D posix_memalign(0x7fffaec50b28, 4096, 16385)
>> 2021/09/15 08:49:50 socat[2215] D posix_memalign(...) -> 0
>> 2021/09/15 08:49:50 socat[2215] N starting data transfer loop with FDs [0,1] and [5,5]
>> 2021/09/15 08:49:50 socat[2215] D data loop: sock1->eof=0, sock2->eof=0, closing=0, wasaction=1, total_to={0.000000}
>> 2021/09/15 08:49:50 socat[2215] D select(6, &0x21, &0x22, &0x0, NULL/0.000000)
>> 2021/09/15 08:49:50 socat[2215] D select -> (, 0x21, 0x22, 0x0, NULL/0.000000), 4
>> 2021/09/15 08:49:50 socat[2215] D read(0, 0x55aa5f016000, 8192)
>> 2021/09/15 08:49:50 socat[2215] D read -> 4
>> 2021/09/15 08:49:50 socat[2215] D write(5, 0x55aa5f016000, 4)
>> Pop
>> 2021/09/15 08:49:50 socat[2215] D write -> 4
>> 2021/09/15 08:49:50 socat[2215] I transferred 4 bytes from 0 to 5
>> 2021/09/15 08:49:50 socat[2215] D read(5, 0x55aa5f016000, 8192)
>> 2021/09/15 08:49:50 socat[2215] D read -> 4
>> 2021/09/15 08:49:50 socat[2215] D write(1, 0x55aa5f016000, 4)
>> Pop
>> 2021/09/15 08:49:50 socat[2215] D write -> 4
>> 2021/09/15 08:49:50 socat[2215] I transferred 4 bytes from 5 to 1
>> 2021/09/15 08:49:50 socat[2215] D data loop: sock1->eof=0, sock2->eof=0, closing=0, wasaction=1, total_to={0.000000}
>> 2021/09/15 08:49:50 socat[2215] D select(6, &0x21, &0x22, &0x0, NULL/0.000000)
>> 2021/09/15 08:49:50 socat[2215] D select -> (, 0x21, 0x22, 0x0, NULL/0.000000), 4
>> 2021/09/15 08:49:50 socat[2215] D read(0, 0x55aa5f016000, 8192)
>> 2021/09/15 08:49:50 socat[2215] D read -> 0
>> 2021/09/15 08:49:50 socat[2215] D read(5, 0x55aa5f016000, 8192)
>> 2021/09/15 08:49:50 socat[2215] D read -> 0
>> 2021/09/15 08:49:50 socat[2215] N socket 1 (fd 0) is at EOF
>> 2021/09/15 08:49:50 socat[2215] I shutdown(5, 1)
>> 2021/09/15 08:49:50 socat[2215] D shutdown() -> 0
>> 2021/09/15 08:49:50 socat[2215] N socket 2 (fd 5) is at EOF
>> 2021/09/15 08:49:50 socat[2215] I shutdown(5, 2)
>> 2021/09/15 08:49:50 socat[2215] D shutdown() -> 0
>> 2021/09/15 08:49:50 socat[2215] N exiting with status 0
>> 2021/09/15 08:49:50 socat[2215] D exit(0)
>> 2021/09/15 08:49:50 socat[2215] D starting xioexit()
>> 2021/09/15 08:49:50 socat[2215] D finished xioexit()
>> uds-access RC=0
>> 2021/09/15 08:49:52 socat[2240] D getpid()
>> 2021/09/15 08:49:52 socat[2240] D getpid() -> 2240
>> 2021/09/15 08:49:52 socat[2240] D setenv("SOCAT_PID", "2240", 1)
>> 2021/09/15 08:49:52 socat[2240] D setenv() -> 0
>> 2021/09/15 08:49:52 socat[2240] D setenv("SOCAT_PPID", "2240", 1)
>> 2021/09/15 08:49:52 socat[2240] D setenv() -> 0
>> 2021/09/15 08:49:52 socat[2240] I socat by Gerhard Rieger and contributors - see www.dest-unreach.org
>> 2021/09/15 08:49:52 socat[2240] I This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. (http://www.openssl.org/)
>> 2021/09/15 08:49:52 socat[2240] I This product includes software written by Tim Hudson (tjh@xxxxxxxxxxxxx)
>> 2021/09/15 08:49:52 socat[2240] D socat version 1.7.4.1 on Jan 27 2021 00:00:00
>> 2021/09/15 08:49:52 socat[2240] D setenv("SOCAT_VERSION", "1.7.4.1", 1)
>> 2021/09/15 08:49:52 socat[2240] D setenv() -> 0
>> 2021/09/15 08:49:52 socat[2240] D running on Linux version #58 SMP Wed Sep 15 08:40:38 PDT 2021, release 5.15.0-rc1bisect, machine x86_64
>>
>> 2021/09/15 08:49:52 socat[2240] D argv[0]: "socat"
>> 2021/09/15 08:49:52 socat[2240] D argv[1]: "-d"
>> 2021/09/15 08:49:52 socat[2240] D argv[2]: "-d"
>> 2021/09/15 08:49:52 socat[2240] D argv[3]: "-d"
>> 2021/09/15 08:49:52 socat[2240] D argv[4]: "-d"
>> 2021/09/15 08:49:52 socat[2240] D argv[5]: "-"
>> 2021/09/15 08:49:52 socat[2240] D argv[6]: "UNIX-CONNECT:./targets/uds-notroot/uds-access-socket"
>> 2021/09/15 08:49:52 socat[2240] D sigaction(1, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(2, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(3, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(4, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(6, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(7, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(8, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(11, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D sigaction(15, 0x7ffcca7e26c0, 0x0)
>> 2021/09/15 08:49:52 socat[2240] D sigaction() -> 0
>> 2021/09/15 08:49:52 socat[2240] D signal(13, 0x1)
>> 2021/09/15 08:49:52 socat[2240] D signal() -> 0x0
>> 2021/09/15 08:49:52 socat[2240] D atexit(0x560590a15110)
>> 2021/09/15 08:49:52 socat[2240] D atexit() -> 0
>> 2021/09/15 08:49:52 socat[2240] D xioopen("-")
>> 2021/09/15 08:49:52 socat[2240] D calloc(1, 824)
>> 2021/09/15 08:49:52 socat[2240] D calloc() -> 0x560591e899d0
>> 2021/09/15 08:49:52 socat[2240] D malloc(1024)
>> 2021/09/15 08:49:52 socat[2240] D malloc() -> 0x560591e89d30
>> 2021/09/15 08:49:52 socat[2240] D calloc(1, 824)
>> 2021/09/15 08:49:52 socat[2240] D calloc() -> 0x560591e8a140
>> 2021/09/15 08:49:52 socat[2240] D calloc(1, 824)
>> 2021/09/15 08:49:52 socat[2240] D calloc() -> 0x560591e8abc0
>> 2021/09/15 08:49:52 socat[2240] D isatty(0)
>> 2021/09/15 08:49:52 socat[2240] D isatty() -> 0
>> 2021/09/15 08:49:52 socat[2240] D isatty(1)
>> 2021/09/15 08:49:52 socat[2240] D isatty() -> 0
>> 2021/09/15 08:49:52 socat[2240] D malloc(128)
>> 2021/09/15 08:49:52 socat[2240] D malloc() -> 0x560591e8af00
>> 2021/09/15 08:49:52 socat[2240] D malloc(128)
>> 2021/09/15 08:49:52 socat[2240] D malloc() -> 0x560591e8af90
>> 2021/09/15 08:49:52 socat[2240] N reading from and writing to stdio
>> 2021/09/15 08:49:52 socat[2240] D xioopen("UNIX-CONNECT:./targets/uds-notroot/uds-access-socket")
>> 2021/09/15 08:49:52 socat[2240] D calloc(1, 824)
>> 2021/09/15 08:49:52 socat[2240] D calloc() -> 0x560591e8b020
>> 2021/09/15 08:49:52 socat[2240] D malloc(1024)
>> 2021/09/15 08:49:52 socat[2240] D malloc() -> 0x560591e8b360
>> 2021/09/15 08:49:52 socat[2240] D malloc(128)
>> 2021/09/15 08:49:52 socat[2240] D malloc() -> 0x560591e8b770
>> 2021/09/15 08:49:52 socat[2240] N opening connection to AF=1 "./targets/uds-notroot/uds-access-socket"
>> 2021/09/15 08:49:52 socat[2240] D socket(1, 1, 0)
>> 2021/09/15 08:49:52 socat[2240] I socket(1, 1, 0) -> 5
>> 2021/09/15 08:49:52 socat[2240] D fcntl(5, 2, 1)
>> 2021/09/15 08:49:52 socat[2240] D fcntl() -> 0
>> 2021/09/15 08:49:52 socat[2240] D connect(5, {1,AF=1 "./targets/uds-notroot/uds-access-socket"}, 41)
>> 2021/09/15 08:49:52 socat[2240] D connect() -> 0
>> 2021/09/15 08:49:52 socat[2240] D getsockname(5, 0x7ffcca7e20f0, 0x7ffcca7e20d4{112})
>> 2021/09/15 08:49:52 socat[2240] D getsockname(, {AF=1 "<anon>"}, {2}) -> 0
>> 2021/09/15 08:49:52 socat[2240] N successfully connected from local address AF=1 "uds-notroot/ud\xEE\xEE\xEE\xEEcess-socket")\n"
>> 2021/09/15 08:49:52 socat[2240] I resolved and opened all sock addresses
>> 2021/09/15 08:49:52 socat[2240] D posix_memalign(0x7ffcca7e2698, 4096, 16385)
>> 2021/09/15 08:49:52 socat[2240] D posix_memalign(...) -> 0
>> 2021/09/15 08:49:52 socat[2240] N starting data transfer loop with FDs [0,1] and [5,5]
>> 2021/09/15 08:49:52 socat[2240] D data loop: sock1->eof=0, sock2->eof=0, closing=0, wasaction=1, total_to={0.000000}
>> 2021/09/15 08:49:52 socat[2240] D select(6, &0x21, &0x22, &0x0, NULL/0.000000)
>> 2021/09/15 08:49:52 socat[2240] D select -> (, 0x1, 0x22, 0x0, NULL/0.000000), 3
>> 2021/09/15 08:49:52 socat[2240] D read(0, 0x560591e8c000, 8192)
>> 2021/09/15 08:49:52 socat[2240] D read -> 5
>> 2021/09/15 08:49:52 socat[2240] D write(5, 0x560591e8c000, 5)
>> 2021/09/15 08:49:52 socat[2240] D write -> 5
>> 2021/09/15 08:49:52 socat[2240] I transferred 5 bytes from 0 to 5
>> 2021/09/15 08:49:52 socat[2240] D data loop: sock1->eof=0, sock2->eof=0, closing=0, wasaction=1, total_to={0.000000}
>> 2021/09/15 08:49:52 socat[2240] D select(6, &0x21, &0x20, &0x0, NULL/0.000000)
>> 2021/09/15 08:49:52 socat[2240] D select -> (, 0x1, 0x20, 0x0, NULL/0.000000), 2
>> 2021/09/15 08:49:52 socat[2240] D read(0, 0x560591e8c000, 8192)
>> 2021/09/15 08:49:52 socat[2240] D read -> 0
>> 2021/09/15 08:49:52 socat[2240] N socket 1 (fd 0) is at EOF
>> 2021/09/15 08:49:52 socat[2240] I shutdown(5, 1)
>> 2021/09/15 08:49:52 socat[2240] D shutdown() -> 0
> Is this shutdown expected?

I'm not an expert on the internals of socat, but I don't think it
is expected.

> 2021/09/15 08:49:52 socat[2240] D data loop: sock1->eof=3, sock2->eof=0, closing=1, wasaction=1, total_to={0.000000}
> 2021/09/15 08:49:52 socat[2240] D select(6, &0x20, &0x0, &0x0, &0.500000)
> Snap
> 2021/09/15 08:49:52 socat[2240] D select -> (, 0x20, 0x0, 0x0, &0.500000), 1
> 2021/09/15 08:49:52 socat[2240] D read(5, 0x560591e8c000, 8192)
> 2021/09/15 08:49:52 socat[2240] D read -> -1
> This read failure seems due to the previous shutdown, right?

Again, I'm not the socat expert, but that would seem reasonable
to me.

>> 2021/09/15 08:49:52 socat[2240] E read(5, 0x560591e8c000, 8192): Invalid argument
>> 2021/09/15 08:49:52 socat[2240] N exit(1)
>> 2021/09/15 08:49:52 socat[2240] D starting xioexit()
>> 2021/09/15 08:49:52 socat[2240] I shutdown(5, 2)
>> 2021/09/15 08:49:52 socat[2240] D shutdown() -> 0
>> 2021/09/15 08:49:52 socat[2240] D finished xioexit()
>> uds-access RC=1
>>
>>
>>
>>

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