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Tue, 23 Jan 2024 10:35:05 -0500 (EST) From: Tycho Andersen To: Christian Brauner Cc: Oleg Nesterov , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Tycho Andersen , Tycho Andersen Subject: [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group leaders Date: Tue, 23 Jan 2024 08:34:50 -0700 Message-Id: <20240123153452.170866-2-tycho@tycho.pizza> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240123153452.170866-1-tycho@tycho.pizza> References: <20240123153452.170866-1-tycho@tycho.pizza> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tycho Andersen We are using the pidfd family of syscalls with the seccomp userspace notifier. When some thread triggers a seccomp notification, we want to do some things to its context (munge fd tables via pidfd_getfd(), maybe write to its memory, etc.). However, threads created with ~CLONE_FILES or ~CLONE_VM mean that we can't use the pidfd family of syscalls for this purpose, since their fd table or mm are distinct from the thread group leader's. In this patch, we relax this restriction for pidfd_open(). In order to avoid dangling poll() users we need to notify pidfd waiters when individual threads die, but once we do that all the other machinery seems to work ok viz. the tests. But I suppose there are more cases than just this one. Signed-off-by: Tycho Andersen -- v2: unify pidfd notification to all go through do_notify_pidfd() inside of __exit_signals() suggested by Oleg. Link to v1: https://lore.kernel.org/all/20231130163946.277502-1-tycho@t= ycho.pizza/ v3: go back to two separate call sites, the exiting one in do_notify_parent(), and a new one in release_task(), when a thread is not the thread group leader. --- include/linux/sched/signal.h | 1 + kernel/exit.c | 11 +++++++++++ kernel/fork.c | 4 +--- kernel/pid.c | 11 +---------- kernel/signal.c | 2 +- 5 files changed, 15 insertions(+), 14 deletions(-) diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 4b7664c56208..d752f003a69a 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -333,6 +333,7 @@ extern int kill_pid_usb_asyncio(int sig, int errno, sig= val_t addr, struct pid *, extern int kill_pgrp(struct pid *pid, int sig, int priv); extern int kill_pid(struct pid *pid, int sig, int priv); extern __must_check bool do_notify_parent(struct task_struct *, int); +extern void do_notify_pidfd(struct task_struct *task); extern void __wake_up_parent(struct task_struct *p, struct task_struct *pa= rent); extern void force_sig(int); extern void force_fatal_sig(int); diff --git a/kernel/exit.c b/kernel/exit.c index 3988a02efaef..90117d7861f4 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -256,6 +256,17 @@ void release_task(struct task_struct *p) write_lock_irq(&tasklist_lock); ptrace_release_task(p); thread_pid =3D get_pid(p->thread_pid); + + /* + * If we're not the leader, notify any waiters on our pidfds. Note that + * we don't want to notify the leader until /everyone/ in the thread + * group is dead, viz. the condition below. + * + * We have to do this here, since __exit_signal() will + * __unhash_processes(), and break do_notify_pidfd()'s lookup. + */ + if (!thread_group_leader(p)) + do_notify_pidfd(p); __exit_signal(p); =20 /* diff --git a/kernel/fork.c b/kernel/fork.c index 47ff3b35352e..44969cd472f0 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2157,8 +2157,6 @@ static int __pidfd_prepare(struct pid *pid, unsigned = int flags, struct file **re * Allocate a new file that stashes @pid and reserve a new pidfd number in= the * caller's file descriptor table. The pidfd is reserved but not installed= yet. * - * The helper verifies that @pid is used as a thread group leader. - * * If this function returns successfully the caller is responsible to eith= er * call fd_install() passing the returned pidfd and pidfd file as argument= s in * order to install the pidfd into its file descriptor table or they must = use @@ -2176,7 +2174,7 @@ static int __pidfd_prepare(struct pid *pid, unsigned = int flags, struct file **re */ int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret) { - if (!pid || !pid_has_task(pid, PIDTYPE_TGID)) + if (!pid) return -EINVAL; =20 return __pidfd_prepare(pid, flags, ret); diff --git a/kernel/pid.c b/kernel/pid.c index b52b10865454..b55c0adf457b 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -552,11 +552,6 @@ struct pid *pidfd_get_pid(unsigned int fd, unsigned in= t *flags) * Return the task associated with @pidfd. The function takes a reference = on * the returned task. The caller is responsible for releasing that referen= ce. * - * Currently, the process identified by @pidfd is always a thread-group le= ader. - * This restriction currently exists for all aspects of pidfds including p= idfd - * creation (CLONE_PIDFD cannot be used with CLONE_THREAD) and pidfd polli= ng - * (only supports thread group leaders). - * * Return: On success, the task_struct associated with the pidfd. * On error, a negative errno number will be returned. */ @@ -615,11 +610,7 @@ int pidfd_create(struct pid *pid, unsigned int flags) * @flags: flags to pass * * This creates a new pid file descriptor with the O_CLOEXEC flag set for - * the process identified by @pid. Currently, the process identified by - * @pid must be a thread-group leader. This restriction currently exists - * for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot - * be used with CLONE_THREAD) and pidfd polling (only supports thread group - * leaders). + * the process identified by @pid. * * Return: On success, a cloexec pidfd is returned. * On error, a negative errno number will be returned. diff --git a/kernel/signal.c b/kernel/signal.c index c9c57d053ce4..3e3c9d0fa3a5 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2019,7 +2019,7 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid= , enum pid_type type) return ret; } =20 -static void do_notify_pidfd(struct task_struct *task) +void do_notify_pidfd(struct task_struct *task) { struct pid *pid; =20 --=20 2.34.1