Re: [PATCH v6 15/16] exec: Fix dead-lock in de_thread with ptrace_attach
From: Bernd Edlinger <hidden>
Date: 2020-03-29 06:36:41
Also in:
linux-api, linux-fsdevel, linux-mm, lkml, stable
Subsystem:
ptrace support, the rest · Maintainers:
Oleg Nesterov, Linus Torvalds
Possibly related (same subject, not in this thread)
- 2020-03-21 · [PATCH v6 15/16] exec: Fix dead-lock in de_thread with ptrace_attach · Bernd Edlinger <hidden>
On 3/29/20 6:31 AM, Bernd Edlinger wrote:
On 3/25/20 3:27 PM, Eric W. Biederman wrote:quoted
Bernd Edlinger [off-list ref] writes: At a minimum the code is subtle and I don't see big fat warning comments that subtle code needs to keep people from using it wrong.Okay, I can add big fat warning comments, yeah.
So how about that:
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 221759e..2d6b5cd 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c@@ -395,6 +395,17 @@ static int ptrace_attach(struct task_struct *task, long req if (mutex_lock_interruptible(&task->signal->exec_guard_mutex)) goto out; + /* + * BIG FAT WARNING - Fragile code ahead. + * Please do not insert any code between these two + * if statements. It may happen that execve has to + * release the exec_guard_mutex in order to prevent + * deadlocks. In that case unsafe_execve_in_progress + * will be set. If that happens you cannot assume that + * the usual guarantees implied by exec_guard_mutex + * are valid. Just return -EAGAIN in that case and + * unlock the mutex immediately. + */ retval = -EAGAIN; if (unlikely(task->signal->unsafe_execve_in_progress)) goto unlock_creds;
Is that cool enough :-) Thanks Bernd.