During exec some file descriptors are closed and the files struct is unshared. But all of that can happen at other times and it has the same protections during exec as at ordinary times. So stop taking the cred_guard_mutex as it is useless.
Furthermore he cred_guard_mutex is a bad idea because it is deadlock prone, as it is held in serveral while waiting possibly indefinitely for userspace to do something.
Cc: Sargun Dhillon sargun@sargun.me Cc: Christian Brauner christian.brauner@ubuntu.com Cc: Arnd Bergmann arnd@arndb.de Fixes: 8649c322f75c ("pid: Implement pidfd_getfd syscall") Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com --- kernel/pid.c | 6 ------ 1 file changed, 6 deletions(-)
Christian if you don't have any objections I will take this one through my tree.
I tried to figure out why this code path takes the cred_guard_mutex and the archive on lore.kernel.org was not helpful in finding that part of the conversation.
diff --git a/kernel/pid.c b/kernel/pid.c index 60820e72634c..53646d5616d2 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -577,17 +577,11 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd) struct file *file; int ret;
- ret = mutex_lock_killable(&task->signal->cred_guard_mutex); - if (ret) - return ERR_PTR(ret); - if (ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)) file = fget_task(task, fd); else file = ERR_PTR(-EPERM);
- mutex_unlock(&task->signal->cred_guard_mutex); - return file ?: ERR_PTR(-EBADF); }