diff options
| author | Pavel Tikhomirov <ptikhomirov@virtuozzo.com> | 2026-03-18 13:21:49 +0100 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2026-03-20 14:44:25 +0100 |
| commit | d9c857aee2ebcdf5e9d81718b78b7966b8eee876 (patch) | |
| tree | f4003aa6169b05bf5907a37f208de86600490509 /kernel | |
| parent | 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681 (diff) | |
pid_namespace: avoid optimization of accesses to ->child_reaper
To avoid potential problems related to cpu/compiler optimizations around
->child_reaper, let's use WRITE_ONCE (additional to task_list lock)
everywhere we write it and use READ_ONCE where we read it without
explicit lock. Note: It also pairs with existing READ_ONCE with no lock
in nsfs_fh_to_dentry().
Also let's add ASSERT_EXCLUSIVE_WRITER before write to identify to KCSAN
that we don't expect any concurrent ->child_reaper modifications, and
those must be detected.
--
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Link: https://patch.msgid.link/20260318122157.280595-2-ptikhomirov@virtuozzo.com
v3: Split from main commit. Add ASSERT_EXCLUSIVE_WRITER.
v5: Add one more READ_ONCE for access without lock in free_pid().
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/exit.c | 3 | ||||
| -rw-r--r-- | kernel/fork.c | 5 | ||||
| -rw-r--r-- | kernel/pid.c | 4 |
3 files changed, 8 insertions, 4 deletions
diff --git a/kernel/exit.c b/kernel/exit.c index ede3117fa7d4..31b714c3a791 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -608,7 +608,8 @@ static struct task_struct *find_child_reaper(struct task_struct *father, reaper = find_alive_thread(father); if (reaper) { - pid_ns->child_reaper = reaper; + ASSERT_EXCLUSIVE_WRITER(pid_ns->child_reaper); + WRITE_ONCE(pid_ns->child_reaper, reaper); return reaper; } diff --git a/kernel/fork.c b/kernel/fork.c index 65113a304518..874670450996 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2423,7 +2423,10 @@ __latent_entropy struct task_struct *copy_process( init_task_pid(p, PIDTYPE_SID, task_session(current)); if (is_child_reaper(pid)) { - ns_of_pid(pid)->child_reaper = p; + struct pid_namespace *ns = ns_of_pid(pid); + + ASSERT_EXCLUSIVE_WRITER(ns->child_reaper); + WRITE_ONCE(ns->child_reaper, p); p->signal->flags |= SIGNAL_UNKILLABLE; } p->signal->shared_pending.signal = delayed.signal; diff --git a/kernel/pid.c b/kernel/pid.c index 3b96571d0fe6..386e51fcebb3 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -128,7 +128,7 @@ void free_pid(struct pid *pid) * is the reaper wake up the reaper. The reaper * may be sleeping in zap_pid_ns_processes(). */ - wake_up_process(ns->child_reaper); + wake_up_process(READ_ONCE(ns->child_reaper)); break; case PIDNS_ADDING: /* Handle a fork failure of the first process */ @@ -219,7 +219,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *arg_set_tid, * Also fail if a PID != 1 is requested and * no PID 1 exists. */ - if (tid != 1 && !tmp->child_reaper) + if (tid != 1 && !READ_ONCE(tmp->child_reaper)) goto out_abort; retval = -EPERM; if (!checkpoint_restore_ns_capable(tmp->user_ns)) |