The following commit has been merged into the perf/core branch of tip:
Commit-ID: 78af4dc949daaa37b3fcd5f348f373085b4e858f
Gitweb:
https://git.kernel.org/tip/78af4dc949daaa37b3fcd5f348f373085b4e858f
Author: pet...@infradead.org <pet...@infradead.org>
AuthorDate: Fri, 28 Aug 2020 14:37:20 +02:00
Committer: Peter Zijlstra <pet...@infradead.org>
CommitterDate: Wed, 09 Dec 2020 17:08:57 +01:00
perf: Break deadlock involving exec_update_mutex
Syzbot reported a lock inversion involving perf. The sore point being
perf holding exec_update_mutex() for a very long time, specifically
across a whole bunch of filesystem ops in pmu::event_init() (uprobes)
and anon_inode_getfile().
This then inverts against procfs code trying to take
exec_update_mutex.
Move the permission checks later, such that we need to hold the mutex
over less code.
Reported-by: syzbot+db9cdf3dd1f64252c...@syzkaller.appspotmail.com
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
kernel/events/core.c | 46 +++++++++++++++++++++----------------------
1 file changed, 23 insertions(+), 23 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a21b0be..19ae6c9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11832,24 +11832,6 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_task;
}
- if (task) {
- err =
mutex_lock_interruptible(&task->signal->exec_update_mutex);
- if (err)
- goto err_task;
-
- /*
- * Preserve ptrace permission check for backwards compatibility.
- *
- * 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).
- */
- err = -EACCES;
- if (!perfmon_capable() && !ptrace_may_access(task,
PTRACE_MODE_READ_REALCREDS))
- goto err_cred;
- }
-
if (flags & PERF_FLAG_PID_CGROUP)
cgroup_fd = pid;
@@ -11857,7 +11839,7 @@ SYSCALL_DEFINE5(perf_event_open,
NULL, NULL, cgroup_fd);
if (IS_ERR(event)) {
err = PTR_ERR(event);
- goto err_cred;
+ goto err_task;
}
if (is_sampling_event(event)) {
@@ -11976,6 +11958,24 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_context;
}
+ if (task) {
+ err =
mutex_lock_interruptible(&task->signal->exec_update_mutex);
+ if (err)
+ goto err_file;
+
+ /*
+ * Preserve ptrace permission check for backwards compatibility.
+ *
+ * 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).
+ */
+ err = -EACCES;
+ if (!perfmon_capable() && !ptrace_may_access(task,
PTRACE_MODE_READ_REALCREDS))
+ goto err_cred;
+ }
+
if (move_group) {
gctx = __perf_event_ctx_lock_double(group_leader, ctx);
@@ -12151,7 +12151,10 @@ err_locked:
if (move_group)
perf_event_ctx_unlock(group_leader, gctx);
mutex_unlock(&ctx->mutex);
-/* err_file: */
+err_cred:
+ if (task)
+ mutex_unlock(&task->signal->exec_update_mutex);
+err_file:
fput(event_file);
err_context:
perf_unpin_context(ctx);
@@ -12163,9 +12166,6 @@ err_alloc:
*/
if (!event_file)
free_event(event);
-err_cred:
- if (task)
- mutex_unlock(&task->signal->exec_update_mutex);
err_task:
if (task)
put_task_struct(task);
