[PATCH 4/4] perf: Use new infrastructure to fix deadlocks in execve

Bernd Edlinger
2020-03-10T17:46:04Z

This changes perf_event_set_clock to use the new exec_update_mutex
instead of cred_guard_mutex.

This should be safe, as the credentials are only used for reading.

Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
---
kernel/events/core.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2173c23..c37f6eb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1248,7 +1248,7 @@ static void put_ctx(struct perf_event_context *ctx)
* function.
*
* Lock order:
- * cred_guard_mutex
+ * exec_update_mutex
* task_struct::perf_event_mutex
* perf_event_context::mutex
* perf_event::child_mutex;
@@ -11254,14 +11254,14 @@ static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id)
}

if (task) {
- err = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
+ err = mutex_lock_interruptible(&task->signal->exec_update_mutex);
if (err)
goto err_task;

/*
* Reuse ptrace permission checks for now.
*
- * We must hold cred_guard_mutex across this and any potential
+ * We must hold exec_update_mutex across this and any potential
* perf_install_in_context() call for this new event to
* serialize against exec() altering our credentials (and the
* perf_event_exit_task() that could imply).
@@ -11550,7 +11550,7 @@ static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id)
mutex_unlock(&ctx->mutex);

if (task) {
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
put_task_struct(task);
}

@@ -11586,7 +11586,7 @@ static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id)
free_event(event);
err_cred:
if (task)
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
err_task:
if (task)
put_task_struct(task);
@@ -11891,7 +11891,7 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
/*
* When a child task exits, feed back event values to parent events.
*
- * Can be called with cred_guard_mutex held when called from
+ * Can be called with exec_update_mutex held when called from
* install_exec_creds().
*/
void perf_event_exit_task(struct task_struct *child)
--
1.9.1