Chris Mason
4e02162a6e
apply_root_directory() calls chroot() but never pairs it with a
chdir("/"). Moving cwd into the new root is left to the subsequent
apply_working_directory() call. That delegation breaks when the unit
sets WorkingDirectory=-/path (working_directory_missing_ok):
apply_root_directory() apply_working_directory()
chroot(new_root) --> chdir(wd) fails (ENOENT)
return 0 return 0 /* missing_ok */
chroot(2) changes only the process root, not cwd. With cwd still
resolving to the pre-chroot host dentry, the process runs with the
kernel root pointing at the new root while relative-path accesses
and /proc/self/cwd reach paths outside RootDirectory=.
Only the chroot-only branch (exec_needs_mount_namespace() == false)
is affected. The mount-namespace branch uses pivot_root(), which
restructures the mount tree and makes the pre-chroot dentry
unreachable.
Fix by issuing chdir("/") immediately after the successful chroot()
in apply_root_directory() and propagating any failure with
EXIT_CHROOT, matching the standard chroot+chdir idiom and making
the chroot self-contained regardless of how
apply_working_directory() later handles a missing directory.
Assisted-by: kres (claude-opus-4-7)
Signed-off-by: Chris Mason <clm@meta.com>
System and Service Manager
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