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Groups > linux.debian.bugs.dist > #1130933

Bug#1027429: mmdebstrap: unshare backend not working

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Hi Andrea,

Quoting Andrea Pappacoda (2022-12-31 12:54:35)
> Hi, for some reason I'm unable to get the unshare backend working on one of
> my machines.
> 
> When I try to create an unstable-amd64 tarball to use with sbuild I get this
> strange error:
> 
>     mmdebstrap --variant=apt --include=build-essential unstable unstable-
> amd64.tar
>     I: automatically chosen mode: unshare
>     I: chroot architecture amd64 is equal to the host's architecture
>     I: automatically chosen format: tar
>     I: using /tmp/mmdebstrap.panqVhWsFm as tempdir
>     W: /etc/subuid is empty
>     E: invalid idmap

Do you have a valid /etc/subuid? Mine says (josch is my username):

josch:100000:65536

How could the error message be improved?

> If I force the creation of the above tarball with root mode

A tarball created in root mode will be bit-by-bit identical to one created in
unshare mode (if SOURCE_DATE_EPOCH was set to the same value).

> and I then try to
> use it in sbuild, I get this even bigger error:
> 
>     Package: yuzu
>     Version: 0-1284+ds-1
>     Source Version: 0-1284+ds-1
>     Distribution: unstable
>     Machine Architecture: amd64
>     Host Architecture: amd64
>     Build Architecture: amd64
>     Build Type: binary
> 
>     Use of uninitialized value $nsid in concatenation (.) or string at
> /usr/share/perl5/Sbuild/Utility.pm line 401.
>     Use of uninitialized value $range in concatenation (.) or string at
> /usr/share/perl5/Sbuild/Utility.pm line 401.
>     Use of uninitialized value $nsid in concatenation (.) or string at
> /usr/share/perl5/Sbuild/Utility.pm line 404.
>     Use of uninitialized value $range in concatenation (.) or string at
> /usr/share/perl5/Sbuild/Utility.pm line 404.
>     Use of uninitialized value $nsid in concatenation (.) or string at
> /usr/share/perl5/Sbuild/Utility.pm line 401.
>     Use of uninitialized value $nsid in concatenation (.) or string at
> /usr/share/perl5/Sbuild/Utility.pm line 404.
>     ranges: 2 argc: 5
>     newuidmap: Not enough arguments to form 2 mappings
>     usage: newuidmap <pid> <uid> <loweruid> <count> [ <uid> <loweruid> <count>
> ] ...
>     newuidmap failed:  at -e line 1.
>     child had a non-zero exit status: 256 at -e line 1.
>     bad exit status (29): perl -e require 'syscall.ph';pipe my $rfh, my $wfh;my
> $ppid = $$;my $cpid = fork() // die "fork() failed: $!";if ($cpid == 0) {close
> $wfh;0 == sysread $rfh, my $c, 1 or die "read() did not receive EOF";0 ==
> system "newuidmap $ppid  0 60092 1 1  1" or die "newuidmap failed: $!";0 ==
> system "newgidmap $ppid  0 60092 1 1  1" or die "newgidmap failed: $!";exit
> 0;}0 == syscall &SYS_unshare, 268435456 or die "unshare() failed: $!";close
> $wfh;$cpid == waitpid $cpid, 0 or die "waitpid() failed: $!";if ($? != 0) {die
> "child had a non-zero exit status: $?";}0 == syscall &SYS_setgid, 0 or die
> "setgid failed: $!";0 == syscall &SYS_setuid, 0 or die "setuid failed: $!";0 ==
> syscall &SYS_setgroups, 0, 0 or die "setgroups failed: $!";exec { $ARGV[0] }
> @ARGV or die "exec() failed: $!"; chown 1:1 /tmp/tmp.sbuild.LKlB9A2jh_
>     E: Error creating chroot session: skipping yuzu
> 
> I've installed this system fairly recently (after the bullseye release), and I
> don't have messed with it that much. One thing that comes to my mind that could
> be messing with UIDs and GIDs is that I'm using systemd-homed to manage my user
> and home directory.
> 
> Under systemd-homed, users aren't saved to /etc/passwd, but are retrievable
> with glibc's NSS API, i.e. with getent(1) and the various getpwuid(3) C
> functions. For instance,
> 
>     $ diff /etc/passwd <(getent passwd)
>     42a43
>     > tachi:x:60092:60092:Andrea Pappacoda:/home/tachi:/usr/bin/zsh
> 
> How could I debug and/or solve this issue? I'm a bit lost.

The error message in sbuild could certainly be improved. Could you try out the
following patch:

diff --git a/lib/Sbuild/ChrootUnshare.pm b/lib/Sbuild/ChrootUnshare.pm
index 9734293a..d48de32d 100644
--- a/lib/Sbuild/ChrootUnshare.pm
+++ b/lib/Sbuild/ChrootUnshare.pm
@@ -105,9 +105,16 @@ sub begin_session {
     my @idmap = read_subuid_subgid;
 
     # sanity check
-    if (scalar(@idmap) != 2 || $idmap[0][0] ne 'u' || $idmap[1][0] ne 'g') {
-       printf STDERR "invalid idmap\n";
-       return 0;
+    if (   scalar(@idmap) != 2
+        || $idmap[0][0] ne 'u'
+        || $idmap[1][0] ne 'g'
+        || length $idmap[0][1] == 0
+        || length $idmap[0][2] == 0
+        || length $idmap[1][1] == 0
+        || length $idmap[1][2] == 0)
+    {
+        printf STDERR "invalid idmap\n";
+        return 0;
     }
 
     $self->set('Uid Gid Map', \@idmap);
diff --git a/lib/Sbuild/Utility.pm b/lib/Sbuild/Utility.pm
index 7405055e..5a59b28a 100644
--- a/lib/Sbuild/Utility.pm
+++ b/lib/Sbuild/Utility.pm
@@ -546,34 +546,28 @@ sub read_subuid_subgid() {
        last if ($n eq $username);
     }
     close $fh;
+
+    if ($n ne $username) {
+       printf STDERR "No entry for $username in /etc/subuid";
+       return;
+    }
+
     push @result, ["u", 0, $subid, $num_subid];
 
-    if (scalar(@result) < 1) {
-       printf STDERR "/etc/subuid does not contain an entry for $username\n";
-       return;
-    }
-    if (scalar(@result) > 1) {
-       printf STDERR "/etc/subuid contains multiple entries for $username\n";
-       return;
-    }
-
     open $fh, "<", "/etc/subgid" or die "cannot open /etc/subgid for reading: $!";
     while (my $line = <$fh>) {
        ($n, $subid, $num_subid) = split(/:/, $line, 3);
        last if ($n eq $username);
     }
     close $fh;
+
+    if ($n ne $username) {
+       printf STDERR "No entry for $username in /etc/subgid";
+       return;
+    }
+
     push @result, ["g", 0, $subid, $num_subid];
 
-    if (scalar(@result) < 2) {
-       printf STDERR "/etc/subgid does not contain an entry for $username\n";
-       return;
-    }
-    if (scalar(@result) > 2) {
-       printf STDERR "/etc/subgid contains multiple entries for $username\n";
-       return;
-    }
-
     return @result;
 }
 

Thanks!

cheers, josch

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Bug#1027429: mmdebstrap: unshare backend not working Andrea Pappacoda <andrea@pappacoda.it> - 2022-12-31 13:00 +0100
  Bug#1027429: mmdebstrap: unshare backend not working Johannes Schauer Marin Rodrigues <josch@debian.org> - 2022-12-31 14:10 +0100
    Bug#1027429: mmdebstrap: unshare backend not working Andrea Pappacoda <andrea@pappacoda.it> - 2022-12-31 16:40 +0100
      Bug#1027429: mmdebstrap: unshare backend not working Johannes Schauer Marin Rodrigues <josch@debian.org> - 2022-12-31 17:50 +0100

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