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>
#include <linux/anon_inodes.h>
#include <linux/file.h>
#include <linux/fs.h>
+#include <linux/cgroup.h>
#include <linux/magic.h>
#include <linux/mount.h>
#include <linux/pid.h>
return poll_flags;
}
+static long pidfd_info(struct task_struct *task, unsigned int cmd, unsigned long arg)
+{
+ struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg;
+ size_t usize = _IOC_SIZE(cmd);
+ struct pidfd_info kinfo = {};
+ struct user_namespace *user_ns;
+ const struct cred *c;
+ __u64 mask;
+#ifdef CONFIG_CGROUPS
+ struct cgroup *cgrp;
+#endif
+
+ if (!uinfo)
+ return -EINVAL;
+ if (usize < PIDFD_INFO_SIZE_VER0)
+ return -EINVAL; /* First version, no smaller struct possible */
+
+ if (copy_from_user(&mask, &uinfo->mask, sizeof(mask)))
+ return -EFAULT;
+
+ c = get_task_cred(task);
+ if (!c)
+ return -ESRCH;
+
+ /* Unconditionally return identifiers and credentials, the rest only on request */
+
+ user_ns = current_user_ns();
+ kinfo.ruid = from_kuid_munged(user_ns, c->uid);
+ kinfo.rgid = from_kgid_munged(user_ns, c->gid);
+ kinfo.euid = from_kuid_munged(user_ns, c->euid);
+ kinfo.egid = from_kgid_munged(user_ns, c->egid);
+ kinfo.suid = from_kuid_munged(user_ns, c->suid);
+ kinfo.sgid = from_kgid_munged(user_ns, c->sgid);
+ kinfo.fsuid = from_kuid_munged(user_ns, c->fsuid);
+ kinfo.fsgid = from_kgid_munged(user_ns, c->fsgid);
+ kinfo.mask |= PIDFD_INFO_CREDS;
+ put_cred(c);
+
+#ifdef CONFIG_CGROUPS
+ rcu_read_lock();
+ cgrp = task_dfl_cgroup(task);
+ kinfo.cgroupid = cgroup_id(cgrp);
+ kinfo.mask |= PIDFD_INFO_CGROUPID;
+ rcu_read_unlock();
+#endif
+
+ /*
+ * Copy pid/tgid last, to reduce the chances the information might be
+ * stale. Note that it is not possible to ensure it will be valid as the
+ * task might return as soon as the copy_to_user finishes, but that's ok
+ * and userspace expects that might happen and can act accordingly, so
+ * this is just best-effort. What we can do however is checking that all
+ * the fields are set correctly, or return ESRCH to avoid providing
+ * incomplete information. */
+
+ kinfo.ppid = task_ppid_nr_ns(task, NULL);
+ kinfo.tgid = task_tgid_vnr(task);
+ kinfo.pid = task_pid_vnr(task);
+ kinfo.mask |= PIDFD_INFO_PID;
+
+ if (kinfo.pid == 0 || kinfo.tgid == 0 || (kinfo.ppid == 0 && kinfo.pid != 1))
+ return -ESRCH;
+
+ /*
+ * If userspace and the kernel have the same struct size it can just
+ * be copied. If userspace provides an older struct, only the bits that
+ * userspace knows about will be copied. If userspace provides a new
+ * struct, only the bits that the kernel knows about will be copied.
+ */
+ if (copy_to_user(uinfo, &kinfo, min(usize, sizeof(kinfo))))
+ return -EFAULT;
+
+ return 0;
+}
+
static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct task_struct *task __free(put_task) = NULL;
struct ns_common *ns_common = NULL;
struct pid_namespace *pid_ns;
- if (arg)
- return -EINVAL;
-
task = get_pid_task(pid, PIDTYPE_PID);
if (!task)
return -ESRCH;
+ /* Extensible IOCTL that does not open namespace FDs, take a shortcut */
+ if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO))
+ return pidfd_info(task, cmd, arg);
+
+ if (arg)
+ return -EINVAL;
+
scoped_guard(task_lock, task) {
nsp = task->nsproxy;
if (nsp)
#define PIDFD_SIGNAL_THREAD_GROUP (1UL << 1)
#define PIDFD_SIGNAL_PROCESS_GROUP (1UL << 2)
+/* Flags for pidfd_info. */
+#define PIDFD_INFO_PID (1UL << 0) /* Always returned, even if not requested */
+#define PIDFD_INFO_CREDS (1UL << 1) /* Always returned, even if not requested */
+#define PIDFD_INFO_CGROUPID (1UL << 2) /* Always returned if available, even if not requested */
+
+#define PIDFD_INFO_SIZE_VER0 64 /* sizeof first published struct */
+
+struct pidfd_info {
+ /*
+ * This mask is similar to the request_mask in statx(2).
+ *
+ * Userspace indicates what extensions or expensive-to-calculate fields
+ * they want by setting the corresponding bits in mask. The kernel
+ * will ignore bits that it does not know about.
+ *
+ * When filling the structure, the kernel will only set bits
+ * corresponding to the fields that were actually filled by the kernel.
+ * This also includes any future extensions that might be automatically
+ * filled. If the structure size is too small to contain a field
+ * (requested or not), to avoid confusion the mask will not
+ * contain a bit for that field.
+ *
+ * As such, userspace MUST verify that mask contains the
+ * corresponding flags after the ioctl(2) returns to ensure that it is
+ * using valid data.
+ */
+ __u64 mask;
+ /*
+ * The information contained in the following fields might be stale at the
+ * time it is received, as the target process might have exited as soon as
+ * the IOCTL was processed, and there is no way to avoid that. However, it
+ * is guaranteed that if the call was successful, then the information was
+ * correct and referred to the intended process at the time the work was
+ * performed. */
+ __u64 cgroupid;
+ __u32 pid;
+ __u32 tgid;
+ __u32 ppid;
+ __u32 ruid;
+ __u32 rgid;
+ __u32 euid;
+ __u32 egid;
+ __u32 suid;
+ __u32 sgid;
+ __u32 fsuid;
+ __u32 fsgid;
+ __u32 spare0[1];
+};
+
#define PIDFS_IOCTL_MAGIC 0xFF
#define PIDFD_GET_CGROUP_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 1)
#define PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 8)
#define PIDFD_GET_USER_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 9)
#define PIDFD_GET_UTS_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 10)
+#define PIDFD_GET_INFO _IOWR(PIDFS_IOCTL_MAGIC, 11, struct pidfd_info)
#endif /* _UAPI_LINUX_PIDFD_H */
#include <stdlib.h>
#include <string.h>
#include <syscall.h>
+#include <sys/ioctl.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/wait.h>
#include "pidfd.h"
#include "../kselftest.h"
+#ifndef PIDFS_IOCTL_MAGIC
+#define PIDFS_IOCTL_MAGIC 0xFF
+#endif
+
+#ifndef PIDFD_GET_INFO
+#define PIDFD_GET_INFO _IOWR(PIDFS_IOCTL_MAGIC, 11, struct pidfd_info)
+#define PIDFD_INFO_CGROUPID (1UL << 0)
+
+struct pidfd_info {
+ __u64 request_mask;
+ __u64 cgroupid;
+ __u32 pid;
+ __u32 tgid;
+ __u32 ppid;
+ __u32 ruid;
+ __u32 rgid;
+ __u32 euid;
+ __u32 egid;
+ __u32 suid;
+ __u32 sgid;
+ __u32 fsuid;
+ __u32 fsgid;
+ __u32 spare0[1];
+};
+#endif
+
static int safe_int(const char *numstr, int *converted)
{
char *err = NULL;
int main(int argc, char **argv)
{
+ struct pidfd_info info = {
+ .request_mask = PIDFD_INFO_CGROUPID,
+ };
int pidfd = -1, ret = 1;
pid_t pid;
- ksft_set_plan(3);
+ ksft_set_plan(4);
pidfd = sys_pidfd_open(-1, 0);
if (pidfd >= 0) {
pid = get_pid_from_fdinfo_file(pidfd, "Pid:", sizeof("Pid:") - 1);
ksft_print_msg("pidfd %d refers to process with pid %d\n", pidfd, pid);
+ if (ioctl(pidfd, PIDFD_GET_INFO, &info) < 0) {
+ ksft_print_msg("%s - failed to get info from pidfd\n", strerror(errno));
+ goto on_error;
+ }
+ if (info.pid != pid) {
+ ksft_print_msg("pid from fdinfo file %d does not match pid from ioctl %d\n",
+ pid, info.pid);
+ goto on_error;
+ }
+ if (info.ppid != getppid()) {
+ ksft_print_msg("ppid %d does not match ppid from ioctl %d\n",
+ pid, info.pid);
+ goto on_error;
+ }
+ if (info.ruid != getuid()) {
+ ksft_print_msg("uid %d does not match uid from ioctl %d\n",
+ getuid(), info.ruid);
+ goto on_error;
+ }
+ if (info.rgid != getgid()) {
+ ksft_print_msg("gid %d does not match gid from ioctl %d\n",
+ getgid(), info.rgid);
+ goto on_error;
+ }
+ if (info.euid != geteuid()) {
+ ksft_print_msg("euid %d does not match euid from ioctl %d\n",
+ geteuid(), info.euid);
+ goto on_error;
+ }
+ if (info.egid != getegid()) {
+ ksft_print_msg("egid %d does not match egid from ioctl %d\n",
+ getegid(), info.egid);
+ goto on_error;
+ }
+ if (info.suid != geteuid()) {
+ ksft_print_msg("suid %d does not match suid from ioctl %d\n",
+ geteuid(), info.suid);
+ goto on_error;
+ }
+ if (info.sgid != getegid()) {
+ ksft_print_msg("sgid %d does not match sgid from ioctl %d\n",
+ getegid(), info.sgid);
+ goto on_error;
+ }
+ if ((info.request_mask & PIDFD_INFO_CGROUPID) && info.cgroupid == 0) {
+ ksft_print_msg("cgroupid should not be 0 when PIDFD_INFO_CGROUPID is set\n");
+ goto on_error;
+ }
+ ksft_test_result_pass("get info from pidfd test: passed\n");
+
ret = 0;
on_error:
projects / thirdparty / linux.git / commitdiff
