| Message ID | 87lfhet1d2.fsf@rdklein.fr |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [bug#43371] doc: prevent host/container nscd mismatch | expand |
| Context | Check | Description |
|---|---|---|
| cbaines/comparison | success | View comparision |
| cbaines/git branch | success | View Git branch |
| cbaines/applying patch | success | View Laminar job |
Hi, edk@beaver-labs.com skribis: > doc/guix.texi: (Name Service Switch) add a workaround for bug #41575 > --- > doc/guix.texi | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > diff --git a/doc/guix.texi b/doc/guix.texi > index a6e14ea177..a9472e680e 100644 > --- a/doc/guix.texi > +++ b/doc/guix.texi > @@ -1706,6 +1706,20 @@ this binary incompatibility problem because those @code{libnss_*.so} > files are loaded in the @command{nscd} process, not in applications > themselves. > > +For applications running in containers (@pxref{Invokin guix container}), > +however, @code{nscd} may leak information from the host to the container. > +If there is a configuration mismatch between the two ---e.g., the host > +has no @code{sshd} user while the container needs one--- then it may be I find the example is hard to understand. How about: “applications in the container could end up looking users in the host”? > +worthwhile to limit which kind of information the host's @code{nscd} > +daemon may give to the container by adding the following to > +@code{/etc/nscd.conf}. > + > +@example > + enable-cache passwd no > + enable-cache group no > + enable-cache netgroup no > +@end example Actually, perhaps the better fix is to never use the host’s nscd? We could change ‘containerized-operating-system’ accordingly. That would allow guest OSes to work correctly regardless of the host’s nscd config, which seems like an improvement. Thoughts? Ludo’.
Hello Ludo', A separate nscd per container also seems like a reasonable option. However, for the sake of machines hosting many long-lived containers, perhaps we should consider reducing the cache size: currently it's 32MB for each name service type, with an expiration of 12-24 hours: https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/base.scm?id=1042d269a723360a02b19a2baafef1e24a3bfc73#n1115 Cheers, Jason On Sun, Sep 13, 2020 at 5:05 PM Ludovic Courtès <ludo@gnu.org> wrote: > Hi, > > edk@beaver-labs.com skribis: > > > doc/guix.texi: (Name Service Switch) add a workaround for bug #41575 > > --- > > doc/guix.texi | 16 +++++++++++++++- > > 1 file changed, 15 insertions(+), 1 deletion(-) > > > > diff --git a/doc/guix.texi b/doc/guix.texi > > index a6e14ea177..a9472e680e 100644 > > --- a/doc/guix.texi > > +++ b/doc/guix.texi > > @@ -1706,6 +1706,20 @@ this binary incompatibility problem because those > @code{libnss_*.so} > > files are loaded in the @command{nscd} process, not in applications > > themselves. > > > > +For applications running in containers (@pxref{Invokin guix container}), > > +however, @code{nscd} may leak information from the host to the > container. > > +If there is a configuration mismatch between the two ---e.g., the host > > +has no @code{sshd} user while the container needs one--- then it may be > > I find the example is hard to understand. How about: “applications in > the container could end up looking users in the host”? > > > +worthwhile to limit which kind of information the host's @code{nscd} > > +daemon may give to the container by adding the following to > > +@code{/etc/nscd.conf}. > > + > > +@example > > + enable-cache passwd no > > + enable-cache group no > > + enable-cache netgroup no > > +@end example > > Actually, perhaps the better fix is to never use the host’s nscd? We > could change ‘containerized-operating-system’ accordingly. > > That would allow guest OSes to work correctly regardless of the host’s > nscd config, which seems like an improvement. > > Thoughts? > > Ludo’. >
Hi ! Ludovic Courtès writes: > Hi, > > edk@beaver-labs.com skribis: > >> doc/guix.texi: (Name Service Switch) add a workaround for bug #41575 >> --- >> doc/guix.texi | 16 +++++++++++++++- >> 1 file changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/doc/guix.texi b/doc/guix.texi >> index a6e14ea177..a9472e680e 100644 >> --- a/doc/guix.texi >> +++ b/doc/guix.texi >> @@ -1706,6 +1706,20 @@ this binary incompatibility problem because those @code{libnss_*.so} >> files are loaded in the @command{nscd} process, not in applications >> themselves. >> >> +For applications running in containers (@pxref{Invokin guix container}), >> +however, @code{nscd} may leak information from the host to the container. >> +If there is a configuration mismatch between the two ---e.g., the host >> +has no @code{sshd} user while the container needs one--- then it may be > > I find the example is hard to understand. How about: “applications in > the container could end up looking users in the host”? > >> +worthwhile to limit which kind of information the host's @code{nscd} >> +daemon may give to the container by adding the following to >> +@code{/etc/nscd.conf}. >> + >> +@example >> + enable-cache passwd no >> + enable-cache group no >> + enable-cache netgroup no >> +@end example > > Actually, perhaps the better fix is to never use the host’s nscd? We > could change ‘containerized-operating-system’ accordingly. > I think this would be best, but I did not know where to make this change, so I just edited the doc instead. I don't know if containers need the host's nscd to avoid the libc issues mentionned in the doc, but if they dont, then prevening them from accessing the host's nscd seems logical and would solve the problem. And we wouldn't need to amend the doc at all. > That would allow guest OSes to work correctly regardless of the host’s > nscd config, which seems like an improvement. > > Thoughts? > > Ludo’.
Hi, conjaroy <conjaroy@gmail.com> skribis: > A separate nscd per container also seems like a reasonable option. However, > for the sake of machines hosting many long-lived containers, perhaps we > should consider reducing the cache size: currently it's 32MB for each name > service type, with an expiration of 12-24 hours: > > https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/base.scm?id=1042d269a723360a02b19a2baafef1e24a3bfc73#n1115 Good point. In that case, we can have ‘containerized-operating-system’ provide its own NSS configuration with a reduced cache size (or without cache since there’s caching happening on the host for host name lookups, for instance). WDYT? Would you like to give it a try? Thanks, Ludo’.
Sure, I'm happy to take a stab at this. Jason On Mon, Sep 14, 2020 at 3:28 AM Ludovic Courtès <ludo@gnu.org> wrote: > In that case, we can have ‘containerized-operating-system’ provide its > own NSS configuration with a reduced cache size (or without cache since > there’s caching happening on the host for host name lookups, for > instance). > > WDYT? Would you like to give it a try? > > Thanks, > Ludo’. > > > >
Hi, Edouard Klein <edou@rdklein.fr> skribis: >> Actually, perhaps the better fix is to never use the host’s nscd? We >> could change ‘containerized-operating-system’ accordingly. >> > > I think this would be best, but I did not know where to make this > change, so I just edited the doc instead. I don't know if containers > need the host's nscd to avoid the libc issues mentionned in the doc, but > if they dont, then prevening them from accessing the host's nscd seems > logical and would solve the problem. And we wouldn't need to amend the > doc at all. This has now been done by Jason in 5627bfe45ce46f498979b4ad2deab1fdfed22b6c. Closing! Ludo’.
Thanks to you both :) Ludovic Courtès writes: > Hi, > > Edouard Klein <edou@rdklein.fr> skribis: > >>> Actually, perhaps the better fix is to never use the host’s nscd? We >>> could change ‘containerized-operating-system’ accordingly. >>> >> >> I think this would be best, but I did not know where to make this >> change, so I just edited the doc instead. I don't know if containers >> need the host's nscd to avoid the libc issues mentionned in the doc, but >> if they dont, then prevening them from accessing the host's nscd seems >> logical and would solve the problem. And we wouldn't need to amend the >> doc at all. > > This has now been done by Jason in > 5627bfe45ce46f498979b4ad2deab1fdfed22b6c. > > Closing! > > Ludo’.
diff --git a/doc/guix.texi b/doc/guix.texi index a6e14ea177..a9472e680e 100644 --- a/doc/guix.texi +++ b/doc/guix.texi @@ -1706,6 +1706,20 @@ this binary incompatibility problem because those @code{libnss_*.so} files are loaded in the @command{nscd} process, not in applications themselves. +For applications running in containers (@pxref{Invokin guix container}), +however, @code{nscd} may leak information from the host to the container. +If there is a configuration mismatch between the two ---e.g., the host +has no @code{sshd} user while the container needs one--- then it may be +worthwhile to limit which kind of information the host's @code{nscd} +daemon may give to the container by adding the following to +@code{/etc/nscd.conf}. + +@example + enable-cache passwd no + enable-cache group no + enable-cache netgroup no +@end example + @subsection X11 Fonts @cindex fonts @@ -27582,7 +27596,7 @@ that should be preferably killed. @item @code{avoid-regexp} (default: @code{#f}) A regular expression (as a string) to match the names of the processes -that should @emph{not} be killed. +that should @emph{not} be kcoilled. @item @code{memory-report-interval} (default: @code{0}) The interval in seconds at which a memory report is printed. It is