Bug#993821: After upgrading libc, some services are unable to restart (including systemd-resolved)

[Michael Biebl]

Control: reassign -1 libc6
Control: found -1 2.32-1
Control: severity -1 serious
Control: affects -1 + systemd

Hi Michael

Am 07.09.21 um 00:39 schrieb Michael Hudson-Doyle:
> On Tue, 7 Sept 2021 at 10:21, Michael Biebl <biebl at debian.org 
> <mailto:biebl at debian.org>> wrote:
> 
>     Am 06.09.21 um 23:45 schrieb Vincent Bernat:
>       > Package: systemd
>       > Version: 247.9-1
>       > Severity: normal
>       >
>      > Hey!
>      >
>      > After upgrading to libc6 2.32-1, some services are unable to restart.
>      > In my case, systemd-resolved, systemd-timesyncd and colord. Using
>      > "systemctl daemon-reexec" fixes the issue. Unsure if there is really
>      > something to be fixed but as I didn't find anything about that, a bug
>      > report may help others. I suppose the problem is related to NSS.
>      >
>      > Sep 06 23:06:43 chocobo systemd[1]: Starting Network Time
>     Synchronization...
>      > Sep 06 23:06:43 chocobo systemd[236983]:
>     systemd-timesyncd.service: Failed to determine user credentials: No
>     such process
>      > Sep 06 23:06:43 chocobo systemd[236983]:
>     systemd-timesyncd.service: Failed at step USER spawning
>     /lib/systemd/systemd-timesyncd: No such process
>      >
>      >
> 
> 
>     @libc maintainers: any ideas what could be causing this? If this is
>     triggered by a libc6 update, should this be reassigned to glibc?
> 
> 
> We went through this in Ubuntu recently and decided that restarting 
> systemd in glibc's postinst was the safest option: 
> https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1942276 
> <https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1942276>
> 
> What's happening is that systemd is running with the old glibc, forks 
> and then does NSS things that cause the new glibc's NSS modules to load 
> and they don't necessarily work, leading to failures in any unit that 
> specifies User=. At least for Ubuntu's builds the NSS modules seem to be 
> ABI compatible between 2.32 and 2.33 (I didn't try 2.31 vs 2.32) but 
> they are definitely not between 2.33 and 2.34.

Thanks for this information. This is indeed an icky issue and I feel 
like we are between a rock and a hard place.
I'm not a huge fan of going back to re-exec systemd again directly in 
libc6.postinst, but your proposed patch to at least check that the 
systemd binary can be sucessfully executed should at least deal with the 
situation sufficiently, where a library is (temporarily) missing.
I do wonder though, if this this will mean that on dist-upgrades the 
daemon-reexec will be skipped.

Anyway, I think it's best to reassign this libc6 for now and mark it as 
RC so the package doesn't migrate to testing for now.

Regards,
Michael

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