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implement dpkg-realpath in perl so that we don't need to run tar inside the chroot anymore for modes other than fakechroot and proot

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This commit is contained in:
Johannes 'josch' Schauer 2020-08-15 18:29:17 +02:00
parent dc67c1f4be
commit c2c270390b
Signed by untrusted user: josch
GPG key ID: F2CBA5C78FBD83E1
1 changed files with 105 additions and 30 deletions
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135
mmdebstrap
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@ -2585,6 +2585,49 @@ sub checkokthx {
return;
}
# resolve a path inside a chroot
sub chrooted_realpath {
my $root = shift;
my $src = shift;
my $result = $root;
my $prefix;
# relative paths are relative to the root of the chroot
# remove prefixed slashes
$src =~ s{^/+}{};
my $loop = 0;
while (length $src) {
if ($loop > 25) {
error "too many levels of symbolic links";
}
# Get the first directory component.
($prefix, $src) = split m{/+}, $src, 2;
# Resolve the first directory component.
if ($prefix eq ".") {
# Ignore, stay at the same directory.
} elsif ($prefix eq "..") {
# Go up one directory.
$result =~ s{(.*)/[^/]*}{$1};
# but not further than the root
if ($result !~ m/^\Q$root\E/) {
$result = $root;
}
} elsif (-l "$result/$prefix") {
my $dst = readlink "$result/$prefix";
if ($dst =~ s{^/+}{}) {
# Absolute pathname, reset result back to $root.
$result = $root;
}
$src = length $src ? "$dst/$src" : $dst;
$loop++;
} else {
# Otherwise append the prefix.
$result = "$result/$prefix";
}
}
return $result;
}
sub hookhelper {
# we put everything in an eval block because that way we can easily handle
# errors without goto labels or much code duplication: the error handler
@ -2597,15 +2640,6 @@ sub hookhelper {
$verbosity_level = $ARGV[5];
my $command = $ARGV[6];
# unless we are in the setup hook (where there is no tar inside the
# chroot) we need to run tar on the inside because otherwise, possible
# absolute symlinks in the path given via --directory are not
# correctly resolved
#
# FIXME: the issue above can be fixed by a function that is able to
# resolve absolute symlinks even inside the chroot directory to a full
# path that is valid on the outside -- fakechroot and proot have their
# own reasons, see below
my @cmdprefix = ();
my @tarcmd = (
'tar', '--numeric-owner', '--xattrs', '--format=pax',
@ -2634,7 +2668,7 @@ sub hookhelper {
push @cmdprefix, 'proot', '--root-id', "--rootfs=$root",
'--cwd=/', "--qemu=$qemu";
} elsif (any { $_ eq $mode } ('root', 'chrootless', 'unshare')) {
push @cmdprefix, '/usr/sbin/chroot', $root;
# not chrooting in this case
} else {
error "unknown mode: $mode";
}
@ -2657,21 +2691,43 @@ sub hookhelper {
# outside
my $directory;
if ($hook eq 'setup') {
$directory = "$root/$outpath";
# tar runs outside, so acquire the correct path
$directory = chrooted_realpath $root, $outpath;
} elsif (
any { $_ eq $hook }
('extract', 'essential', 'customize')
) {
$directory = $outpath;
if (any { $_ eq $mode } ('fakechroot', 'proot')) {
# tar will run inside the chroot
$directory = $outpath;
} elsif (
any { $_ eq $mode }
('root', 'chrootless', 'unshare')
) {
$directory = chrooted_realpath $root, $outpath;
} else {
error "unknown mode: $mode";
}
} else {
error "unknown hook: $hook";
}
# FIXME: here we would like to check if the path inside the
# chroot given by $directory actually exists but we cannot
# because we are missing a function that can resolve even
# paths including absolute symlinks to paths that are valid
# outside the chroot
# if chrooted_realpath was used and if neither fakechroot or
# proot were used (absolute symlinks will be broken) we can
# check and potentially fail early if the target does not exist
if (none { $_ eq $mode } ('fakechroot', 'proot')) {
my $dirtocheck = $directory;
if ($command eq 'upload') {
# check the parent directory instead
$dirtocheck =~ s/(.*)\/[^\/]*/$1/;
}
if (!-e $dirtocheck) {
error "path does not exist: $dirtocheck";
}
if (!-d $dirtocheck) {
error "path is not a directory: $dirtocheck";
}
}
my $fh;
if ($command eq 'upload') {
@ -2779,21 +2835,40 @@ sub hookhelper {
# outside
my $directory;
if ($hook eq 'setup') {
$directory = "$root/$ARGV[$i]";
# tar runs outside, so acquire the correct path
$directory = chrooted_realpath $root, $ARGV[$i];
} elsif (
any { $_ eq $hook }
('extract', 'essential', 'customize')
) {
$directory = $ARGV[$i];
if (any { $_ eq $mode } ('fakechroot', 'proot')) {
# tar will run inside the chroot
$directory = $ARGV[$i];
} elsif (
any { $_ eq $mode }
('root', 'chrootless', 'unshare')
) {
$directory = chrooted_realpath $root, $ARGV[$i];
} else {
error "unknown mode: $mode";
}
} else {
error "unknown hook: $hook";
}
# FIXME: here we would like to check if the path inside the
# chroot given by $directory actually exists but we cannot
# because we are missing a function that can resolve even
# paths including absolute symlinks to paths that are valid
# outside the chroot
# if chrooted_realpath was used and if neither fakechroot or
# proot were used (absolute symlinks will be broken) we can
# check and potentially fail early if the source does not exist
if (none { $_ eq $mode } ('fakechroot', 'proot')) {
if (!-e $directory) {
error "path does not exist: $directory";
}
if ($command eq 'download') {
if (!-f $directory) {
error "path is not a file: $directory";
}
}
}
my $fh;
if ($command eq 'download') {
@ -5444,12 +5519,12 @@ The path on the outside is relative to current directory of the original
B<mmdebstrap> invocation. The path inside the chroot must already exist. Paths
outside the chroot are created as necessary.
To be able to resolve even absolute symlinks, C<tar> or C<sh> and C<cat> are
executed inside the chroot for the B<essential> and B<customize> hooks. This
means that the special hooks might fail for the B<extract> and B<custom>
variants if no C<tar> or C<sh> and C<cat> is available inside the chroot.
Since nothing is yet installed at the time of the B<setup> hook, no absolute
symlinks in paths inside the chroot are supported during that hook.
In B<fakechroot> and B<proot> mode, C<tar>, or C<sh> and C<cat> have to be run
inside the chroot or otherwise, symlinks will be wrongly resolved and/or
permissions will be off. This means that the special hooks might fail in
B<fakechroot> and B<proot> mode for the B<setup> hook or for the B<extract> and
B<custom> variants if no C<tar> or C<sh> and C<cat> is available inside the
chroot.
=over 8