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Mark the range from -10000 to -40000 as a range reserved for special
in-kernel values. Move the PIDFD_SELF_*/PIDFD_THREAD_* sentinels over so
all the special values are in one place.
Link: https://lore.kernel.org/20250624-work-pidfs-fhandle-v2-6-d02a04858fe3@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Extend the PIDFD_INFO_COREDUMP ioctl() with the new PIDFD_INFO_COREDUMP
mask flag. This adds the @coredump_mask field to struct pidfd_info.
When a task coredumps the kernel will provide the following information
to userspace in @coredump_mask:
* PIDFD_COREDUMPED is raised if the task did actually coredump.
* PIDFD_COREDUMP_SKIP is raised if the task skipped coredumping (e.g.,
undumpable).
* PIDFD_COREDUMP_USER is raised if this is a regular coredump and
doesn't need special care by the coredump server.
* PIDFD_COREDUMP_ROOT is raised if the generated coredump should be
treated as sensitive and the coredump server should restrict to the
generated coredump to sufficiently privileged users.
The kernel guarantees that by the time the connection is made the all
PIDFD_INFO_COREDUMP info is available.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-5-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Fold it into pidfd_prepare() and rename PIDFD_CLONE to PIDFD_STALE to
indicate that the passed pid might not have task linkage and no explicit
check for that should be performed.
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-3-450a19461e75@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: David Rheinsberg <david@readahead.eu>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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When we currently create a pidfd we check that the task hasn't been
reaped right before we create the pidfd. But it is of course possible
that by the time we return the pidfd to userspace the task has already
been reaped since we don't check again after having created a dentry for
it.
This was fine until now because that race was meaningless. But now that
we provide PIDFD_INFO_EXIT it is a problem because it is possible that
the kernel returns a reaped pidfd and it depends on the race whether
PIDFD_INFO_EXIT information is available. This depends on if the task
gets reaped before or after a dentry has been attached to struct pid.
Make this consistent and only returned pidfds for reaped tasks if
PIDFD_INFO_EXIT information is available. This is done by performing
another check whether the task has been reaped right after we attached a
dentry to struct pid.
Since pidfs_exit() is called before struct pid's task linkage is removed
the case where the task got reaped but a dentry was already attached to
struct pid and exit information was recorded and published can be
handled correctly. In that case we do return a pidfd for a reaped task
like we would've before.
Link: https://lore.kernel.org/r/20250316-kabel-fehden-66bdb6a83436@brauner
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Some tools like systemd's jounral need to retrieve the exit and cgroup
information after a process has already been reaped. This can e.g.,
happen when retrieving a pidfd via SCM_PIDFD or SCM_PEERPIDFD.
Link: https://lore.kernel.org/r/20250305-work-pidfs-kill_on_last_close-v3-6-c8c3d8361705@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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It is useful to be able to utilise the pidfd mechanism to reference the
current thread or process (from a userland point of view - thread group
leader from the kernel's point of view).
Therefore introduce PIDFD_SELF_THREAD to refer to the current thread, and
PIDFD_SELF_THREAD_GROUP to refer to the current thread group leader.
For convenience and to avoid confusion from userland's perspective we alias
these:
* PIDFD_SELF is an alias for PIDFD_SELF_THREAD - This is nearly always what
the user will want to use, as they would find it surprising if for
instance fd's were unshared()'d and they wanted to invoke pidfd_getfd()
and that failed.
* PIDFD_SELF_PROCESS is an alias for PIDFD_SELF_THREAD_GROUP - Most users
have no concept of thread groups or what a thread group leader is, and
from userland's perspective and nomenclature this is what userland
considers to be a process.
We adjust pidfd_get_task() and the pidfd_send_signal() system call with
specific handling for this, implementing this functionality for
process_madvise(), process_mrelease() (albeit, using it here wouldn't
really make sense) and pidfd_send_signal().
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/r/24315a16a3d01a548dd45c7515f7d51c767e954e.1738268370.git.lorenzo.stoakes@oracle.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
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A common pattern when using pid fds is having to get information
about the process, which currently requires /proc being mounted,
resolving the fd to a pid, and then do manual string parsing of
/proc/N/status and friends. This needs to be reimplemented over
and over in all userspace projects (e.g.: I have reimplemented
resolving in systemd, dbus, dbus-daemon, polkit so far), and
requires additional care in checking that the fd is still valid
after having parsed the data, to avoid races.
Having a programmatic API that can be used directly removes all
these requirements, including having /proc mounted.
As discussed at LPC24, add an ioctl with an extensible struct
so that more parameters can be added later if needed. Start with
returning pid/tgid/ppid and creds unconditionally, and cgroupid
optionally.
Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Link: https://lore.kernel.org/r/20241010155401.2268522-1-luca.boccassi@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
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For users that hold a reference to a pidfd procfs might not even be
available nor is it desirable to parse through procfs just for the sake
of getting namespace file descriptors for a process.
Make it possible to directly retrieve namespace file descriptors from a
pidfd. Pidfds already can be used with setns() to change a set of
namespaces atomically.
Link: https://lore.kernel.org/r/20240627-work-pidfs-v1-4-7e9ab6cc3bb1@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Right now we determine the scope of the signal based on the type of
pidfd. There are use-cases where it's useful to override the scope of
the signal. For example in [1]. Add flags to determine the scope of the
signal:
(1) PIDFD_SIGNAL_THREAD: send signal to specific thread reference by @pidfd
(2) PIDFD_SIGNAL_THREAD_GROUP: send signal to thread-group of @pidfd
(2) PIDFD_SIGNAL_PROCESS_GROUP: send signal to process-group of @pidfd
Since we now allow specifying PIDFD_SEND_PROCESS_GROUP for
pidfd_send_signal() to send signals to process groups we need to adjust
the check restricting si_code emulation by userspace to account for
PIDTYPE_PGID.
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://github.com/systemd/systemd/issues/31093 [1]
Link: https://lore.kernel.org/r/20240210-chihuahua-hinzog-3945b6abd44a@brauner
Link: https://lore.kernel.org/r/20240214123655.GB16265@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
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With this flag:
- pidfd_open() doesn't require that the target task must be
a thread-group leader
- pidfd_poll() succeeds when the task exits and becomes a
zombie (iow, passes exit_notify()), even if it is a leader
and thread-group is not empty.
This means that the behaviour of pidfd_poll(PIDFD_THREAD,
pid-of-group-leader) is not well defined if it races with
exec() from its sub-thread; pidfd_poll() can succeed or not
depending on whether pidfd_task_exited() is called before
or after exchange_tids().
Perhaps we can improve this behaviour later, pidfd_poll()
can probably take sig->group_exec_task into account. But
this doesn't really differ from the case when the leader
exits before other threads (so pidfd_poll() succeeds) and
then another thread execs and pidfd_poll() will block again.
thread_group_exited() is no longer used, perhaps it can die.
Co-developed-by: Tycho Andersen <tycho@tycho.pizza>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20240131132602.GA23641@redhat.com
Tested-by: Tycho Andersen <tandersen@netflix.com>
Reviewed-by: Tycho Andersen <tandersen@netflix.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Introduce PIDFD_NONBLOCK to support non-blocking pidfd file descriptors.
Ever since the introduction of pidfds and more advanced async io various
programming languages such as Rust have grown support for async event
libraries. These libraries are created to help build epoll-based event loops
around file descriptors. A common pattern is to automatically make all file
descriptors they manage to O_NONBLOCK.
For such libraries the EAGAIN error code is treated specially. When a function
is called that returns EAGAIN the function isn't called again until the event
loop indicates the the file descriptor is ready. Supporting EAGAIN when
waiting on pidfds makes such libraries just work with little effort. In the
following patch we will extend waitid() internally to support non-blocking
pidfds.
This introduces a new flag PIDFD_NONBLOCK that is equivalent to O_NONBLOCK.
This follows the same patterns we have for other (anon inode) file descriptors
such as EFD_NONBLOCK, IN_NONBLOCK, SFD_NONBLOCK, TFD_NONBLOCK and the same for
close-on-exec flags.
Suggested-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/lkml/20200811181236.GA18763@localhost/
Link: https://github.com/joshtriplett/async-pidfd
Link: https://lore.kernel.org/r/20200902102130.147672-2-christian.brauner@ubuntu.com
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