[PATCH] tracing/user_events: Fail fork when event state duplication fails
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HOTtoday
From: Jeff Barnes <hidden>
Date: 2026-10-02 22:26:49
Also in:
lkml
Subsystem:
exec & binfmt api, elf, memory management - core, scheduler, the rest, tracing · Maintainers:
Kees Cook, Andrew Morton, David Hildenbrand, Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
Registered user events are retained across fork, but duplicating their
state for a child with a separate mm can fail. Both user_event_mm_dup() and
user_events_fork() currently return void, so allocation failure silently
creates a child without the inherited registration state.
The child can consequently retain a stale copy-on-write enable word and
miss later event enable and disable updates.
Return an error from user_event_mm_dup() and user_events_fork(), and
perform the duplication in copy_process() while failure can still be
unwound. Return -ENOMEM when the child user_event_mm or any of its enablers
cannot be duplicated.
Add a cleanup path so successfully acquired user-events state is removed if
a later fork operation fails. Preserve the existing CLONE_VM behavior and
its task reference accounting.
A deterministic allocation-failure test on upstream master previously
allowed fork() to succeed while the child missed an enablement update. With
this change, the same fork fails with ENOMEM. The complete user_events ABI
suite passes.
Fixes: 7235759084a4 ("tracing/user_events: Use remote writes for event enablement")
Cc: stable@vger.kernel.org
Signed-off-by: Jeff Barnes <redacted>
---
include/linux/user_events.h | 16 +++++++---------
kernel/fork.c | 8 ++++++--
kernel/trace/trace_events_user.c | 8 +++++---
3 files changed, 18 insertions(+), 14 deletions(-)
diff --git a/include/linux/user_events.h b/include/linux/user_events.h
index 57d1ff006090..75f184126727 100644
--- a/include/linux/user_events.h
+++ b/include/linux/user_events.h@@ -27,28 +27,26 @@ struct user_event_mm { struct rcu_work put_rwork; }; -extern void user_event_mm_dup(struct task_struct *t, - struct user_event_mm *old_mm); +int user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm); extern void user_event_mm_remove(struct task_struct *t); -static inline void user_events_fork(struct task_struct *t, - u64 clone_flags) +static inline int user_events_fork(struct task_struct *t, u64 clone_flags) { struct user_event_mm *old_mm; if (!t || !current->user_event_mm) - return; + return 0; old_mm = current->user_event_mm; if (clone_flags & CLONE_VM) { t->user_event_mm = old_mm; refcount_inc(&old_mm->tasks); - return; + return 0; } - user_event_mm_dup(t, old_mm); + return user_event_mm_dup(t, old_mm); } static inline void user_events_execve(struct task_struct *t)
@@ -67,9 +65,9 @@ static inline void user_events_exit(struct task_struct *t) user_event_mm_remove(t); } #else -static inline void user_events_fork(struct task_struct *t, - u64 clone_flags) +static inline int user_events_fork(struct task_struct *t, u64 clone_flags) { + return 0; } static inline void user_events_execve(struct task_struct *t)
diff --git a/kernel/fork.c b/kernel/fork.c
index 10f2d05d816a..9e3da2e6059f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c@@ -2311,9 +2311,12 @@ __latent_entropy struct task_struct *copy_process( retval = copy_mm(clone_flags, p); if (retval) goto bad_fork_cleanup_signal; - retval = copy_namespaces(clone_flags, p); + retval = user_events_fork(p, clone_flags); if (retval) goto bad_fork_cleanup_mm; + retval = copy_namespaces(clone_flags, p); + if (retval) + goto bad_fork_cleanup_user_events; retval = copy_io(clone_flags, p); if (retval) goto bad_fork_cleanup_namespaces;
@@ -2575,7 +2578,6 @@ __latent_entropy struct task_struct *copy_process( trace_task_newtask(p, clone_flags); uprobe_copy_process(p, clone_flags); - user_events_fork(p, clone_flags); copy_oom_score_adj(clone_flags, p);
@@ -2602,6 +2604,8 @@ __latent_entropy struct task_struct *copy_process( exit_io_context(p); bad_fork_cleanup_namespaces: exit_nsproxy_namespaces(p); +bad_fork_cleanup_user_events: + user_events_exit(p); bad_fork_cleanup_mm: sched_cache_fork_cleanup(p); if (p->mm) {
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index f658c3a77aa7..8941c8d7c193 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c@@ -863,7 +863,7 @@ void user_event_mm_remove(struct task_struct *t) queue_rcu_work(system_percpu_wq, &mm->put_rwork); } -void user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm) +int user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm) { struct user_event_mm *mm = user_event_mm_alloc(t); struct user_event_enabler *enabler;
@@ -872,7 +872,7 @@ void user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm) t->user_event_mm = NULL; if (!mm) - return; + return -ENOMEM; rcu_read_lock();
@@ -884,10 +884,12 @@ void user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm) rcu_read_unlock(); user_event_mm_attach(mm, t); - return; + return 0; error: rcu_read_unlock(); user_event_mm_destroy(mm); + + return -ENOMEM; } static bool current_user_event_enabler_exists(unsigned long uaddr,
--
2.43.0