diff options
| author | Tycho Andersen <tandersen@netflix.com> | 2024-02-07 10:19:29 +0100 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2024-02-07 12:09:44 +0100 |
| commit | 0c9bd6bc4bb2ecfe8ce12e9a77ccd762dabe18b4 (patch) | |
| tree | 1dbd5b043ffe82884c4e95b1c7aa9bd8afef273e | |
| parent | 83b290c9e3b5d95891f43a4aeadf6071cbff25d3 (diff) | |
pidfd: getfd should always report ESRCH if a task is exiting
We can get EBADF from pidfd_getfd() if a task is currently exiting,
which might be confusing. Let's check PF_EXITING, and just report ESRCH
if so.
I chose PF_EXITING, because it is set in exit_signals(), which is called
before exit_files(). Since ->exit_status is mostly set after
exit_files() in exit_notify(), using that still leaves a window open for
the race.
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Tycho Andersen <tandersen@netflix.com>
Link: https://lore.kernel.org/r/20240206192357.81942-1-tycho@tycho.pizza
Signed-off-by: Christian Brauner <brauner@kernel.org>
| -rw-r--r-- | kernel/pid.c | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/kernel/pid.c b/kernel/pid.c index de0bf2f8d18b..c1d940fbd314 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -678,7 +678,26 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd) up_read(&task->signal->exec_update_lock); - return file ?: ERR_PTR(-EBADF); + if (!file) { + /* + * It is possible that the target thread is exiting; it can be + * either: + * 1. before exit_signals(), which gives a real fd + * 2. before exit_files() takes the task_lock() gives a real fd + * 3. after exit_files() releases task_lock(), ->files is NULL; + * this has PF_EXITING, since it was set in exit_signals(), + * __pidfd_fget() returns EBADF. + * In case 3 we get EBADF, but that really means ESRCH, since + * the task is currently exiting and has freed its files + * struct, so we fix it up. + */ + if (task->flags & PF_EXITING) + file = ERR_PTR(-ESRCH); + else + file = ERR_PTR(-EBADF); + } + + return file; } static int pidfd_getfd(struct pid *pid, int fd) |