[Bug nss/28300] New: move of nss_files functions into libc breaks NSS ABI stability

[Bug nss/28300] New: move of nss_files functions into libc breaks NSS ABI stability

[michael.hudson at canonical dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28300

            Bug ID: 28300
           Summary: move of nss_files functions into libc breaks NSS ABI
                    stability
           Product: glibc
           Version: 2.34
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: nss
          Assignee: unassigned at sourceware dot org
          Reporter: michael.hudson at canonical dot com
  Target Milestone: ---

I should start by saying that I'm not really sure how much this counts as a
bug. But anyway:

This mail to libc-alpha:

https://sourceware.org/legacy-ml/libc-help/2016-12/msg00006.html

says:

TLDR; You can mix any NSS modules you want with any version of glibc. The
dlopen
and dlsym interface used isolates you from ABI issues. 

But the change to move nss_files functions into libc in 2.34 means this is no
longer true: If code running glibc 2.33 dlopens nss_files from 2.34, nothing
works.

This is causing a problem in Ubuntu where systemd cannot start services that
have a User= or Group= setting:
https://bugs.launchpad.net/ubuntu/+source/docker.io/+bug/1942276

Perhaps we need to fix this by restarting systemd when updating libc (although
this was stopped due to this bug
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=753725 which I haven't really
understood yet) but anyway, this change appears to contradict stated policy so
I thought I'd mention it. (I certainly don't know how to fix it in glibc -- I
guess symbol versioning games of some kind might do the trick).

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[Bug nss/28300] move of nss_files functions into libc breaks NSS ABI stability

[michael.hudson at canonical dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28300

Michael Hudson-Doyle <michael.hudson at canonical dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |michael.hudson at canonical dot co
                   |                            |m

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[Bug nss/28300] move of nss_files functions into libc breaks NSS ABI stability

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28300

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> ---
The NSS modules have always been closely tied to the glibc version, given they
are using GLIBC_PRIVATE interfaces.

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[Bug nss/28300] move of nss_files functions into libc breaks NSS ABI stability

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28300

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |fweimer at redhat dot com
         Resolution|---                         |NOTABUG

--- Comment #2 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to Michael Hudson-Doyle from comment #0)
> I should start by saying that I'm not really sure how much this counts as a
> bug. But anyway:
> 
> This mail to libc-alpha:
> 
> https://sourceware.org/legacy-ml/libc-help/2016-12/msg00006.html
> 
> says:
> 
> TLDR; You can mix any NSS modules you want with any version of glibc. The
> dlopen and dlsym interface used isolates you from ABI issues. 

>From the context (“[We] are trying […] to properly integrate third-party NSS
modules into NixOS”) it is clear that this refers to external NSS modules, not
the NSS modules which are part of glibc.

On the plus side, after the change in glibc 2.34, this problem goes away
completely for nss_files and nss_dns (the most widely used NSS modules).

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