From: Tao Cui Since Linux 4.9, /proc/locks only shows locks whose owning process is visible in the reader's pid namespace. The check cannot see the owner of an OFD lock, though: locks_translate_pid() always returns -1 for FL_OFDLCK, so an OFD lock held outside of that namespace bypasses the filter and is shown with its device/inode numbers and byte range, e.g. 4: OFDLCK ADVISORY WRITE -1 fd:00:70536961 0 EOF This was observed on a Kubernetes node: a pod reading /proc/locks listed the OFD write lock of an unrelated host process, while the POSIX locks of the very same process were correctly hidden. The device/inode pair identifies which host file is locked, the byte range discloses where it is actively written, and the appearance/disappearance of entries reflects host task activity, contrary to the documented per-pidns visibility of /proc/locks (proc_locks(5)). OFD locks record the owner tgid in flc_pid, so use it for the visibility decision in locks_show(), mirroring what locks_translate_pid() does for POSIX locks. The pid column is still reported as -1 for OFD locks; only the filter decision changes. Remote locks keep their negative flc_pid and stay visible as before. Verified with an OFD and a POSIX write lock held in the initial pid namespace while a process in a fresh pid namespace reads /proc/locks: the OFD entry is visible without this patch and hidden with it, the POSIX entry is hidden in both cases. Signed-off-by: Tao Cui --- Changes since v1: keep remote OFD locks (negative flc_pid) visible in non-initial pid namespaces, as locks_translate_pid() does for remote POSIX locks. --- fs/locks.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/fs/locks.c b/fs/locks.c index 6e4ff7fcec05..4af1385682e4 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -3022,6 +3022,25 @@ static int locks_show(struct seq_file *f, void *v) cur = hlist_entry(v, struct file_lock_core, flc_link); + /* + * OFD locks are reported with pid -1, so the filter below cannot see + * their owner; flc_pid holds the owner tgid, so filter on it. + * Remote locks keep a negative flc_pid and stay visible as before. + */ + if ((cur->flc_flags & FL_OFDLCK) && cur->flc_pid > 0 && + proc_pidns != &init_pid_ns) { + struct pid *pid; + bool visible = false; + + rcu_read_lock(); + pid = find_pid_ns(cur->flc_pid, &init_pid_ns); + if (pid) + visible = pid_nr_ns(pid, proc_pidns) != 0; + rcu_read_unlock(); + if (!visible) + return 0; + } + if (locks_translate_pid(cur, proc_pidns) == 0) return 0; -- 2.43.0