kernel/linux.git/include/uapi/linux/pidfd.h, branch v6.19.11

pidfs: expose coredump signal

2025-10-30T13:25:14+00:00

Userspace needs access to the signal that caused the coredump before the coredumping process has been reaped. Expose it as part of the coredump information in struct pidfd_info. After the process has been reaped that info is also available as part of PIDFD_INFO_EXIT's exit_code field. Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-8-ca449b7b7aa0@kernel.org Reviewed-by: Alexander Mikhalitsyn Reviewed-by: Oleg Nesterov Signed-off-by: Christian Brauner

pidfd: add a new supported_mask field

2025-10-30T13:25:13+00:00

Some of the future fields in struct pidfd_info can be optional. If the kernel has nothing to emit in that field, then it doesn't set the flag in the reply. This presents a problem: There is currently no way to know what mask flags the kernel supports since one can't always count on them being in the reply. Add a new PIDFD_INFO_SUPPORTED_MASK flag and field that the kernel can set in the reply. Userspace can use this to determine if the fields it requires from the kernel are supported. This also gives us a way to deprecate fields in the future, if that should become necessary. Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-5-ca449b7b7aa0@kernel.org Reviewed-by: Alexander Mikhalitsyn Reviewed-by: Oleg Nesterov Signed-off-by: Christian Brauner

pidfs: add missing PIDFD_INFO_SIZE_VER1

2025-10-30T13:25:13+00:00

We grew struct pidfd_info not too long ago. Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-3-ca449b7b7aa0@kernel.org Fixes: 1d8db6fd698d ("pidfs, coredump: add PIDFD_INFO_COREDUMP") Reviewed-by: Alexander Mikhalitsyn Reviewed-by: Oleg Nesterov Signed-off-by: Christian Brauner

uapi/fcntl: mark range as reserved

2025-06-24T13:50:06+00:00

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 Reviewed-by: Amir Goldstein Signed-off-by: Christian Brauner

pidfs, coredump: add PIDFD_INFO_COREDUMP

2025-05-21T11:59:12+00:00

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 Reviewed-by: Alexander Mikhalitsyn Reviewed-by: Jann Horn Signed-off-by: Christian Brauner

pidfs: get rid of __pidfd_prepare()

2025-04-26T06:28:03+00:00

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 Reviewed-by: David Rheinsberg Signed-off-by: Christian Brauner

pidfs: ensure that PIDFS_INFO_EXIT is available

2025-03-19T13:40:18+00:00

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 Signed-off-by: Christian Brauner

pidfs: allow to retrieve exit information

2025-03-05T12:26:17+00:00

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 Reviewed-by: Oleg Nesterov Signed-off-by: Christian Brauner

pidfd: add PIDFD_SELF* sentinels to refer to own thread/process

2025-02-05T14:14:37+00:00

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 Link: https://lore.kernel.org/r/24315a16a3d01a548dd45c7515f7d51c767e954e.1738268370.git.lorenzo.stoakes@oracle.com Signed-off-by: Christian Brauner

pidfd: add ioctl to retrieve pid info

2024-10-24T11:54:51+00:00

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 Link: https://lore.kernel.org/r/20241010155401.2268522-1-luca.boccassi@gmail.com Signed-off-by: Christian Brauner