On 3/29/20 6:31 AM, Bernd Edlinger wrote:
> On 3/25/20 3:27 PM, Eric W. Biederman wrote:
>> Bernd Edlinger <bernd.edlinger@xxxxxxxxxx> 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.
