Re: setns() affecting other threads in 5.10.132 and 6.0

[Thorsten Leemhuis <regressions@leemhuis.info>]

TWIMC: this mail is primarily send for documentation purposes and for
regzbot, my Linux kernel regression tracking bot. These mails usually
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[TLDR: I'm adding this regression report to the list of tracked
regressions; all text from me you find below is based on a few templates
paragraphs you might have encountered already already in similar form.]

Hi, this is your Linux kernel regression tracker. CCing the regression
mailing list, as it should be in the loop for all regressions, as
explained here:
https://www.kernel.org/doc/html/latest/admin-guide/reporting-issues.html

On 04.09.22 16:05, David Laight wrote:
> Sometime after 5.10.105 (5.10.132 and 6.0) there is a change that
> makes setns(open("/proc/1/ns/net")) in the main process change
> the behaviour of other process threads.
> 
> I don't know how much is broken, but the following fails.
> 
> Create a network namespace (eg "test").
> Create a 'bond' interface (eg "test0") in the namespace.
> 
> Then /proc/net/bonding/test0 only exists inside the namespace.
> 
> However if you run a program in the "test" namespace that does:
> - create a thread.
> - change the main thread to in "init" namespace.
> - try to open /proc/net/bonding/test0 in the thread.
> then the open fails.
> 
> I don't know how much else is affected and haven't tried
> to bisect (I can't create bonds on my normal test kernel).
> 
> The test program below shows the problem.
> Compile and run as:
> # ip netns exec test strace -f test_prog /proc/net/bonding/test0
> 
> The second open by the child should succeed, but fails.
> 
> I can't see any changes to the bonding code, so I suspect
> it is something much more fundamental.
> It might only affect /proc/net, but it might also affect
> which namespace sockets get created in.
> IIRC ls -l /proc/n/task/*/ns gives the correct namespaces.
> 
> 	David
> 
> 
> #define _GNU_SOURCE
> 
> #include <fcntl.h>
> #include <unistd.h>
> #include <poll.h>
> #include <pthread.h>
> #include <sched.h>
> 
> #define delay(secs) poll(0,0, (secs) * 1000)
> 
> static void *thread_fn(void *file)
> {
>         delay(2);
>         open(file, O_RDONLY);
> 
>         delay(5);
>         open(file, O_RDONLY);
> 
>         return NULL;
> }
> 
> int main(int argc, char **argv)
> {
>         pthread_t id;
> 
>         pthread_create(&id, NULL, thread_fn, argv[1]);
> 
>         delay(1);
>         open(argv[1], O_RDONLY);
> 
>         delay(2);
>         setns(open("/proc/1/ns/net", O_RDONLY), 0);
> 
>         delay(1);
>         open(argv[1], O_RDONLY);
> 
>         delay(4);
> 
>         return 0;
> }
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

Thanks for the report. To be sure below issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, my Linux kernel regression
tracking bot:

#regzbot ^introduced v5.10.105..v5.10.132
#regzbot title setns() affecting other threads (also in 6.0-rc)
#regzbot ignore-activity

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply -- ideally with also
telling regzbot about it, as explained here:
https://linux-regtracking.leemhuis.info/tracked-regression/

Reminder for developers: When fixing the issue, add 'Link:' tags
pointing to the report (the mail this one replies to), as explained for
in the Linux kernel's documentation; above webpage explains why this is
important for tracked regressions.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.