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chrootenv-user: don't unshare user namespace if we are root

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This commit is contained in:
Nikolay Amiantov 2015-12-15 16:46:37 +03:00
parent 83a8e8e4ef
commit 230898ceb2
1 changed files with 25 additions and 14 deletions
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39
pkgs/build-support/build-fhs-userenv/chroot-user.rb
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@ -53,6 +53,7 @@ $unshare = make_fcall 'unshare', [Fiddle::TYPE_INT], Fiddle::TYPE_INT
MS_BIND = 0x1000 MS_BIND = 0x1000
MS_REC = 0x4000 MS_REC = 0x4000
MS_SLAVE = 0x80000
$mount = make_fcall 'mount', [Fiddle::TYPE_VOIDP, $mount = make_fcall 'mount', [Fiddle::TYPE_VOIDP,
Fiddle::TYPE_VOIDP, Fiddle::TYPE_VOIDP,
Fiddle::TYPE_VOIDP, Fiddle::TYPE_VOIDP,
@ -92,23 +93,31 @@ root = Dir.mktmpdir 'chrootenv'
# we don't use threads at all. # we don't use threads at all.
$cpid = $fork.call $cpid = $fork.call
if $cpid == 0 if $cpid == 0
# Save user UID and GID # If we are root, no need to create new user namespace.
uid = Process.uid if Process.uid == 0
gid = Process.gid $unshare.call CLONE_NEWNS
# Mark all mounted filesystems as slave so changes
# don't propagate to the parent mount namespace.
$mount.call nil, '/', nil, MS_REC | MS_SLAVE, nil
else
# Save user UID and GID
uid = Process.uid
gid = Process.gid
# Create new mount and user namespaces # Create new mount and user namespaces
# CLONE_NEWUSER requires a program to be non-threaded, hence # CLONE_NEWUSER requires a program to be non-threaded, hence
# native fork above. # native fork above.
$unshare.call CLONE_NEWNS | CLONE_NEWUSER $unshare.call CLONE_NEWNS | CLONE_NEWUSER
# Map users and groups to the parent namespace # Map users and groups to the parent namespace
begin begin
# setgroups is only available since Linux 3.19 # setgroups is only available since Linux 3.19
write_file '/proc/self/setgroups', 'deny' write_file '/proc/self/setgroups', 'deny'
rescue rescue
end
write_file '/proc/self/uid_map', "#{uid} #{uid} 1"
write_file '/proc/self/gid_map', "#{gid} #{gid} 1"
end end
write_file '/proc/self/uid_map', "#{uid} #{uid} 1"
write_file '/proc/self/gid_map', "#{gid} #{gid} 1"
# Do rbind mounts. # Do rbind mounts.
mounts.each do |from, rto| mounts.each do |from, rto|
@ -117,6 +126,8 @@ if $cpid == 0
$mount.call from, to, nil, MS_BIND | MS_REC, nil $mount.call from, to, nil, MS_BIND | MS_REC, nil
end end
# Don't make root private so privilege drops inside chroot are possible
File.chmod(0755, root)
# Chroot! # Chroot!
Dir.chroot root Dir.chroot root
Dir.chdir '/' Dir.chdir '/'