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authorpeterz@infradead.org <peterz@infradead.org>2020-08-28 14:37:20 +0200
committerPeter Zijlstra <peterz@infradead.org>2020-12-09 17:08:57 +0100
commit78af4dc949daaa37b3fcd5f348f373085b4e858f (patch)
treefc680c63d7cb4156603b7896d963ac2b272012f1 /kernel/events
parente6e4f42eb773c1da869af4bad544c26c89cd01ab (diff)
downloadlinux-78af4dc949daaa37b3fcd5f348f373085b4e858f.tar.bz2
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+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Diffstat (limited to 'kernel/events')
-rw-r--r--kernel/events/core.c46
1 files changed, 23 insertions, 23 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a21b0be2f22c..19ae6c931c52 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);