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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>
This commit is contained in:
peterz@infradead.org 2020-08-28 14:37:20 +02:00 committed by Peter Zijlstra
parent e6e4f42eb7
commit 78af4dc949
1 changed files with 23 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

46
kernel/events/core.c
View File

@ -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);