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-rw-r--r--fs/pidfs.c1104
1 files changed, 1104 insertions, 0 deletions
diff --git a/fs/pidfs.c b/fs/pidfs.c
new file mode 100644
index 000000000000..dba703d4ce4a
--- /dev/null
+++ b/fs/pidfs.c
@@ -0,0 +1,1104 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/anon_inodes.h>
+#include <linux/exportfs.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>
+#include <linux/pidfs.h>
+#include <linux/pid_namespace.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/proc_ns.h>
+#include <linux/pseudo_fs.h>
+#include <linux/ptrace.h>
+#include <linux/seq_file.h>
+#include <uapi/linux/pidfd.h>
+#include <linux/ipc_namespace.h>
+#include <linux/time_namespace.h>
+#include <linux/utsname.h>
+#include <net/net_namespace.h>
+#include <linux/coredump.h>
+#include <linux/xattr.h>
+
+#include "internal.h"
+#include "mount.h"
+
+#define PIDFS_PID_DEAD ERR_PTR(-ESRCH)
+
+static struct kmem_cache *pidfs_attr_cachep __ro_after_init;
+static struct kmem_cache *pidfs_xattr_cachep __ro_after_init;
+
+static struct path pidfs_root_path = {};
+
+void pidfs_get_root(struct path *path)
+{
+ *path = pidfs_root_path;
+ path_get(path);
+}
+
+enum pidfs_attr_mask_bits {
+ PIDFS_ATTR_BIT_EXIT = 0,
+ PIDFS_ATTR_BIT_COREDUMP = 1,
+};
+
+struct pidfs_attr {
+ unsigned long attr_mask;
+ struct simple_xattrs *xattrs;
+ struct /* exit info */ {
+ __u64 cgroupid;
+ __s32 exit_code;
+ };
+ __u32 coredump_mask;
+ __u32 coredump_signal;
+};
+
+static struct rb_root pidfs_ino_tree = RB_ROOT;
+
+#if BITS_PER_LONG == 32
+static inline unsigned long pidfs_ino(u64 ino)
+{
+ return lower_32_bits(ino);
+}
+
+/* On 32 bit the generation number are the upper 32 bits. */
+static inline u32 pidfs_gen(u64 ino)
+{
+ return upper_32_bits(ino);
+}
+
+#else
+
+/* On 64 bit simply return ino. */
+static inline unsigned long pidfs_ino(u64 ino)
+{
+ return ino;
+}
+
+/* On 64 bit the generation number is 0. */
+static inline u32 pidfs_gen(u64 ino)
+{
+ return 0;
+}
+#endif
+
+static int pidfs_ino_cmp(struct rb_node *a, const struct rb_node *b)
+{
+ struct pid *pid_a = rb_entry(a, struct pid, pidfs_node);
+ struct pid *pid_b = rb_entry(b, struct pid, pidfs_node);
+ u64 pid_ino_a = pid_a->ino;
+ u64 pid_ino_b = pid_b->ino;
+
+ if (pid_ino_a < pid_ino_b)
+ return -1;
+ if (pid_ino_a > pid_ino_b)
+ return 1;
+ return 0;
+}
+
+void pidfs_add_pid(struct pid *pid)
+{
+ static u64 pidfs_ino_nr = 2;
+
+ /*
+ * On 64 bit nothing special happens. The 64bit number assigned
+ * to struct pid is the inode number.
+ *
+ * On 32 bit the 64 bit number assigned to struct pid is split
+ * into two 32 bit numbers. The lower 32 bits are used as the
+ * inode number and the upper 32 bits are used as the inode
+ * generation number.
+ *
+ * On 32 bit pidfs_ino() will return the lower 32 bit. When
+ * pidfs_ino() returns zero a wrap around happened. When a
+ * wraparound happens the 64 bit number will be incremented by 2
+ * so inode numbering starts at 2 again.
+ *
+ * On 64 bit comparing two pidfds is as simple as comparing
+ * inode numbers.
+ *
+ * When a wraparound happens on 32 bit multiple pidfds with the
+ * same inode number are likely to exist (This isn't a problem
+ * since before pidfs pidfds used the anonymous inode meaning
+ * all pidfds had the same inode number.). Userspace can
+ * reconstruct the 64 bit identifier by retrieving both the
+ * inode number and the inode generation number to compare or
+ * use file handles.
+ */
+ if (pidfs_ino(pidfs_ino_nr) == 0)
+ pidfs_ino_nr += 2;
+
+ pid->ino = pidfs_ino_nr;
+ pid->stashed = NULL;
+ pid->attr = NULL;
+ pidfs_ino_nr++;
+
+ write_seqcount_begin(&pidmap_lock_seq);
+ rb_find_add_rcu(&pid->pidfs_node, &pidfs_ino_tree, pidfs_ino_cmp);
+ write_seqcount_end(&pidmap_lock_seq);
+}
+
+void pidfs_remove_pid(struct pid *pid)
+{
+ write_seqcount_begin(&pidmap_lock_seq);
+ rb_erase(&pid->pidfs_node, &pidfs_ino_tree);
+ write_seqcount_end(&pidmap_lock_seq);
+}
+
+void pidfs_free_pid(struct pid *pid)
+{
+ struct pidfs_attr *attr __free(kfree) = no_free_ptr(pid->attr);
+ struct simple_xattrs *xattrs __free(kfree) = NULL;
+
+ /*
+ * Any dentry must've been wiped from the pid by now.
+ * Otherwise there's a reference count bug.
+ */
+ VFS_WARN_ON_ONCE(pid->stashed);
+
+ /*
+ * This if an error occurred during e.g., task creation that
+ * causes us to never go through the exit path.
+ */
+ if (unlikely(!attr))
+ return;
+
+ /* This never had a pidfd created. */
+ if (IS_ERR(attr))
+ return;
+
+ xattrs = no_free_ptr(attr->xattrs);
+ if (xattrs)
+ simple_xattrs_free(xattrs, NULL);
+}
+
+#ifdef CONFIG_PROC_FS
+/**
+ * pidfd_show_fdinfo - print information about a pidfd
+ * @m: proc fdinfo file
+ * @f: file referencing a pidfd
+ *
+ * Pid:
+ * This function will print the pid that a given pidfd refers to in the
+ * pid namespace of the procfs instance.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its pid. This is
+ * similar to calling getppid() on a process whose parent is outside of
+ * its pid namespace.
+ *
+ * NSpid:
+ * If pid namespaces are supported then this function will also print
+ * the pid of a given pidfd refers to for all descendant pid namespaces
+ * starting from the current pid namespace of the instance, i.e. the
+ * Pid field and the first entry in the NSpid field will be identical.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its first NSpid
+ * entry and no others will be shown.
+ * Note that this differs from the Pid and NSpid fields in
+ * /proc/<pid>/status where Pid and NSpid are always shown relative to
+ * the pid namespace of the procfs instance. The difference becomes
+ * obvious when sending around a pidfd between pid namespaces from a
+ * different branch of the tree, i.e. where no ancestral relation is
+ * present between the pid namespaces:
+ * - create two new pid namespaces ns1 and ns2 in the initial pid
+ * namespace (also take care to create new mount namespaces in the
+ * new pid namespace and mount procfs)
+ * - create a process with a pidfd in ns1
+ * - send pidfd from ns1 to ns2
+ * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
+ * have exactly one entry, which is 0
+ */
+static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+ struct pid *pid = pidfd_pid(f);
+ struct pid_namespace *ns;
+ pid_t nr = -1;
+
+ if (likely(pid_has_task(pid, PIDTYPE_PID))) {
+ ns = proc_pid_ns(file_inode(m->file)->i_sb);
+ nr = pid_nr_ns(pid, ns);
+ }
+
+ seq_put_decimal_ll(m, "Pid:\t", nr);
+
+#ifdef CONFIG_PID_NS
+ seq_put_decimal_ll(m, "\nNSpid:\t", nr);
+ if (nr > 0) {
+ int i;
+
+ /* If nr is non-zero it means that 'pid' is valid and that
+ * ns, i.e. the pid namespace associated with the procfs
+ * instance, is in the pid namespace hierarchy of pid.
+ * Start at one below the already printed level.
+ */
+ for (i = ns->level + 1; i <= pid->level; i++)
+ seq_put_decimal_ll(m, "\t", pid->numbers[i].nr);
+ }
+#endif
+ seq_putc(m, '\n');
+}
+#endif
+
+/*
+ * Poll support for process exit notification.
+ */
+static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
+{
+ struct pid *pid = pidfd_pid(file);
+ struct task_struct *task;
+ __poll_t poll_flags = 0;
+
+ poll_wait(file, &pid->wait_pidfd, pts);
+ /*
+ * Don't wake waiters if the thread-group leader exited
+ * prematurely. They either get notified when the last subthread
+ * exits or not at all if one of the remaining subthreads execs
+ * and assumes the struct pid of the old thread-group leader.
+ */
+ guard(rcu)();
+ task = pid_task(pid, PIDTYPE_PID);
+ if (!task)
+ poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP;
+ else if (task->exit_state && !delay_group_leader(task))
+ poll_flags = EPOLLIN | EPOLLRDNORM;
+
+ return poll_flags;
+}
+
+static inline bool pid_in_current_pidns(const struct pid *pid)
+{
+ const struct pid_namespace *ns = task_active_pid_ns(current);
+
+ if (ns->level <= pid->level)
+ return pid->numbers[ns->level].ns == ns;
+
+ return false;
+}
+
+static __u32 pidfs_coredump_mask(unsigned long mm_flags)
+{
+ switch (__get_dumpable(mm_flags)) {
+ case SUID_DUMP_USER:
+ return PIDFD_COREDUMP_USER;
+ case SUID_DUMP_ROOT:
+ return PIDFD_COREDUMP_ROOT;
+ case SUID_DUMP_DISABLE:
+ return PIDFD_COREDUMP_SKIP;
+ default:
+ WARN_ON_ONCE(true);
+ }
+
+ return 0;
+}
+
+/* This must be updated whenever a new flag is added */
+#define PIDFD_INFO_SUPPORTED (PIDFD_INFO_PID | \
+ PIDFD_INFO_CREDS | \
+ PIDFD_INFO_CGROUPID | \
+ PIDFD_INFO_EXIT | \
+ PIDFD_INFO_COREDUMP | \
+ PIDFD_INFO_SUPPORTED_MASK | \
+ PIDFD_INFO_COREDUMP_SIGNAL)
+
+static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
+{
+ struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg;
+ struct task_struct *task __free(put_task) = NULL;
+ struct pid *pid = pidfd_pid(file);
+ size_t usize = _IOC_SIZE(cmd);
+ struct pidfd_info kinfo = {};
+ struct user_namespace *user_ns;
+ struct pidfs_attr *attr;
+ const struct cred *c;
+ __u64 mask;
+
+ BUILD_BUG_ON(sizeof(struct pidfd_info) != PIDFD_INFO_SIZE_VER2);
+
+ 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;
+
+ /*
+ * Restrict information retrieval to tasks within the caller's pid
+ * namespace hierarchy.
+ */
+ if (!pid_in_current_pidns(pid))
+ return -ESRCH;
+
+ attr = READ_ONCE(pid->attr);
+ if (mask & PIDFD_INFO_EXIT) {
+ if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) {
+ smp_rmb();
+ kinfo.mask |= PIDFD_INFO_EXIT;
+#ifdef CONFIG_CGROUPS
+ kinfo.cgroupid = attr->cgroupid;
+ kinfo.mask |= PIDFD_INFO_CGROUPID;
+#endif
+ kinfo.exit_code = attr->exit_code;
+ }
+ }
+
+ if (mask & PIDFD_INFO_COREDUMP) {
+ if (test_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask)) {
+ smp_rmb();
+ kinfo.mask |= PIDFD_INFO_COREDUMP | PIDFD_INFO_COREDUMP_SIGNAL;
+ kinfo.coredump_mask = attr->coredump_mask;
+ kinfo.coredump_signal = attr->coredump_signal;
+ }
+ }
+
+ task = get_pid_task(pid, PIDTYPE_PID);
+ if (!task) {
+ /*
+ * If the task has already been reaped, only exit
+ * information is available
+ */
+ if (!(mask & PIDFD_INFO_EXIT))
+ return -ESRCH;
+
+ goto copy_out;
+ }
+
+ c = get_task_cred(task);
+ if (!c)
+ return -ESRCH;
+
+ if ((mask & PIDFD_INFO_COREDUMP) && !kinfo.coredump_mask) {
+ guard(task_lock)(task);
+ if (task->mm) {
+ unsigned long flags = __mm_flags_get_dumpable(task->mm);
+
+ kinfo.coredump_mask = pidfs_coredump_mask(flags);
+ kinfo.mask |= PIDFD_INFO_COREDUMP;
+ /* No coredump actually took place, so no coredump signal. */
+ }
+ }
+
+ /* 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
+ if (!kinfo.cgroupid) {
+ struct cgroup *cgrp;
+
+ 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)
+ return -ESRCH;
+
+copy_out:
+ if (mask & PIDFD_INFO_SUPPORTED_MASK) {
+ kinfo.mask |= PIDFD_INFO_SUPPORTED_MASK;
+ kinfo.supported_mask = PIDFD_INFO_SUPPORTED;
+ }
+
+ /* Are there bits in the return mask not present in PIDFD_INFO_SUPPORTED? */
+ WARN_ON_ONCE(~PIDFD_INFO_SUPPORTED & kinfo.mask);
+ /*
+ * 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.
+ */
+ return copy_struct_to_user(uinfo, usize, &kinfo, sizeof(kinfo), NULL);
+}
+
+static bool pidfs_ioctl_valid(unsigned int cmd)
+{
+ switch (cmd) {
+ case FS_IOC_GETVERSION:
+ case PIDFD_GET_CGROUP_NAMESPACE:
+ case PIDFD_GET_IPC_NAMESPACE:
+ case PIDFD_GET_MNT_NAMESPACE:
+ case PIDFD_GET_NET_NAMESPACE:
+ case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
+ case PIDFD_GET_TIME_NAMESPACE:
+ case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
+ case PIDFD_GET_UTS_NAMESPACE:
+ case PIDFD_GET_USER_NAMESPACE:
+ case PIDFD_GET_PID_NAMESPACE:
+ return true;
+ }
+
+ /* Extensible ioctls require some more careful checks. */
+ switch (_IOC_NR(cmd)) {
+ case _IOC_NR(PIDFD_GET_INFO):
+ /*
+ * Try to prevent performing a pidfd ioctl when someone
+ * erronously mistook the file descriptor for a pidfd.
+ * This is not perfect but will catch most cases.
+ */
+ return extensible_ioctl_valid(cmd, PIDFD_GET_INFO, PIDFD_INFO_SIZE_VER0);
+ }
+
+ return false;
+}
+
+static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+ struct task_struct *task __free(put_task) = NULL;
+ struct nsproxy *nsp __free(put_nsproxy) = NULL;
+ struct ns_common *ns_common = NULL;
+
+ if (!pidfs_ioctl_valid(cmd))
+ return -ENOIOCTLCMD;
+
+ if (cmd == FS_IOC_GETVERSION) {
+ if (!arg)
+ return -EINVAL;
+
+ __u32 __user *argp = (__u32 __user *)arg;
+ return put_user(file_inode(file)->i_generation, argp);
+ }
+
+ /* Extensible IOCTL that does not open namespace FDs, take a shortcut */
+ if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO))
+ return pidfd_info(file, cmd, arg);
+
+ task = get_pid_task(pidfd_pid(file), PIDTYPE_PID);
+ if (!task)
+ return -ESRCH;
+
+ if (arg)
+ return -EINVAL;
+
+ scoped_guard(task_lock, task) {
+ nsp = task->nsproxy;
+ if (nsp)
+ get_nsproxy(nsp);
+ }
+ if (!nsp)
+ return -ESRCH; /* just pretend it didn't exist */
+
+ /*
+ * We're trying to open a file descriptor to the namespace so perform a
+ * filesystem cred ptrace check. Also, we mirror nsfs behavior.
+ */
+ if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
+ return -EACCES;
+
+ switch (cmd) {
+ /* Namespaces that hang of nsproxy. */
+ case PIDFD_GET_CGROUP_NAMESPACE:
+ if (!ns_ref_get(nsp->cgroup_ns))
+ break;
+ ns_common = to_ns_common(nsp->cgroup_ns);
+ break;
+ case PIDFD_GET_IPC_NAMESPACE:
+ if (!ns_ref_get(nsp->ipc_ns))
+ break;
+ ns_common = to_ns_common(nsp->ipc_ns);
+ break;
+ case PIDFD_GET_MNT_NAMESPACE:
+ if (!ns_ref_get(nsp->mnt_ns))
+ break;
+ ns_common = to_ns_common(nsp->mnt_ns);
+ break;
+ case PIDFD_GET_NET_NAMESPACE:
+ if (!ns_ref_get(nsp->net_ns))
+ break;
+ ns_common = to_ns_common(nsp->net_ns);
+ break;
+ case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
+ if (!ns_ref_get(nsp->pid_ns_for_children))
+ break;
+ ns_common = to_ns_common(nsp->pid_ns_for_children);
+ break;
+ case PIDFD_GET_TIME_NAMESPACE:
+ if (!ns_ref_get(nsp->time_ns))
+ break;
+ ns_common = to_ns_common(nsp->time_ns);
+ break;
+ case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
+ if (!ns_ref_get(nsp->time_ns_for_children))
+ break;
+ ns_common = to_ns_common(nsp->time_ns_for_children);
+ break;
+ case PIDFD_GET_UTS_NAMESPACE:
+ if (!ns_ref_get(nsp->uts_ns))
+ break;
+ ns_common = to_ns_common(nsp->uts_ns);
+ break;
+ /* Namespaces that don't hang of nsproxy. */
+ case PIDFD_GET_USER_NAMESPACE:
+ scoped_guard(rcu) {
+ struct user_namespace *user_ns;
+
+ user_ns = task_cred_xxx(task, user_ns);
+ if (!ns_ref_get(user_ns))
+ break;
+ ns_common = to_ns_common(user_ns);
+ }
+ break;
+ case PIDFD_GET_PID_NAMESPACE:
+ scoped_guard(rcu) {
+ struct pid_namespace *pid_ns;
+
+ pid_ns = task_active_pid_ns(task);
+ if (!ns_ref_get(pid_ns))
+ break;
+ ns_common = to_ns_common(pid_ns);
+ }
+ break;
+ default:
+ return -ENOIOCTLCMD;
+ }
+
+ if (!ns_common)
+ return -EOPNOTSUPP;
+
+ /* open_namespace() unconditionally consumes the reference */
+ return open_namespace(ns_common);
+}
+
+static const struct file_operations pidfs_file_operations = {
+ .poll = pidfd_poll,
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = pidfd_show_fdinfo,
+#endif
+ .unlocked_ioctl = pidfd_ioctl,
+ .compat_ioctl = compat_ptr_ioctl,
+};
+
+struct pid *pidfd_pid(const struct file *file)
+{
+ if (file->f_op != &pidfs_file_operations)
+ return ERR_PTR(-EBADF);
+ return file_inode(file)->i_private;
+}
+
+/*
+ * We're called from release_task(). We know there's at least one
+ * reference to struct pid being held that won't be released until the
+ * task has been reaped which cannot happen until we're out of
+ * release_task().
+ *
+ * If this struct pid has at least once been referred to by a pidfd then
+ * pid->attr will be allocated. If not we mark the struct pid as dead so
+ * anyone who is trying to register it with pidfs will fail to do so.
+ * Otherwise we would hand out pidfs for reaped tasks without having
+ * exit information available.
+ *
+ * Worst case is that we've filled in the info and the pid gets freed
+ * right away in free_pid() when no one holds a pidfd anymore. Since
+ * pidfs_exit() currently is placed after exit_task_work() we know that
+ * it cannot be us aka the exiting task holding a pidfd to itself.
+ */
+void pidfs_exit(struct task_struct *tsk)
+{
+ struct pid *pid = task_pid(tsk);
+ struct pidfs_attr *attr;
+#ifdef CONFIG_CGROUPS
+ struct cgroup *cgrp;
+#endif
+
+ might_sleep();
+
+ /* Synchronize with pidfs_register_pid(). */
+ scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) {
+ attr = pid->attr;
+ if (!attr) {
+ /*
+ * No one ever held a pidfd for this struct pid.
+ * Mark it as dead so no one can add a pidfs
+ * entry anymore. We're about to be reaped and
+ * so no exit information would be available.
+ */
+ pid->attr = PIDFS_PID_DEAD;
+ return;
+ }
+ }
+
+ /*
+ * If @pid->attr is set someone might still legitimately hold a
+ * pidfd to @pid or someone might concurrently still be getting
+ * a reference to an already stashed dentry from @pid->stashed.
+ * So defer cleaning @pid->attr until the last reference to @pid
+ * is put
+ */
+
+#ifdef CONFIG_CGROUPS
+ rcu_read_lock();
+ cgrp = task_dfl_cgroup(tsk);
+ attr->cgroupid = cgroup_id(cgrp);
+ rcu_read_unlock();
+#endif
+ attr->exit_code = tsk->exit_code;
+
+ /* Ensure that PIDFD_GET_INFO sees either all or nothing. */
+ smp_wmb();
+ set_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask);
+}
+
+#ifdef CONFIG_COREDUMP
+void pidfs_coredump(const struct coredump_params *cprm)
+{
+ struct pid *pid = cprm->pid;
+ struct pidfs_attr *attr;
+
+ attr = READ_ONCE(pid->attr);
+
+ VFS_WARN_ON_ONCE(!attr);
+ VFS_WARN_ON_ONCE(attr == PIDFS_PID_DEAD);
+
+ /* Note how we were coredumped and that we coredumped. */
+ attr->coredump_mask = pidfs_coredump_mask(cprm->mm_flags) |
+ PIDFD_COREDUMPED;
+ /* If coredumping is set to skip we should never end up here. */
+ VFS_WARN_ON_ONCE(attr->coredump_mask & PIDFD_COREDUMP_SKIP);
+ /* Expose the signal number that caused the coredump. */
+ attr->coredump_signal = cprm->siginfo->si_signo;
+ smp_wmb();
+ set_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask);
+}
+#endif
+
+static struct vfsmount *pidfs_mnt __ro_after_init;
+
+/*
+ * The vfs falls back to simple_setattr() if i_op->setattr() isn't
+ * implemented. Let's reject it completely until we have a clean
+ * permission concept for pidfds.
+ */
+static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+ struct iattr *attr)
+{
+ return anon_inode_setattr(idmap, dentry, attr);
+}
+
+static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
+ struct kstat *stat, u32 request_mask,
+ unsigned int query_flags)
+{
+ return anon_inode_getattr(idmap, path, stat, request_mask, query_flags);
+}
+
+static ssize_t pidfs_listxattr(struct dentry *dentry, char *buf, size_t size)
+{
+ struct inode *inode = d_inode(dentry);
+ struct pid *pid = inode->i_private;
+ struct pidfs_attr *attr = pid->attr;
+ struct simple_xattrs *xattrs;
+
+ xattrs = READ_ONCE(attr->xattrs);
+ if (!xattrs)
+ return 0;
+
+ return simple_xattr_list(inode, xattrs, buf, size);
+}
+
+static const struct inode_operations pidfs_inode_operations = {
+ .getattr = pidfs_getattr,
+ .setattr = pidfs_setattr,
+ .listxattr = pidfs_listxattr,
+};
+
+static void pidfs_evict_inode(struct inode *inode)
+{
+ struct pid *pid = inode->i_private;
+
+ clear_inode(inode);
+ put_pid(pid);
+}
+
+static const struct super_operations pidfs_sops = {
+ .drop_inode = inode_just_drop,
+ .evict_inode = pidfs_evict_inode,
+ .statfs = simple_statfs,
+};
+
+/*
+ * 'lsof' has knowledge of out historical anon_inode use, and expects
+ * the pidfs dentry name to start with 'anon_inode'.
+ */
+static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen)
+{
+ return dynamic_dname(buffer, buflen, "anon_inode:[pidfd]");
+}
+
+const struct dentry_operations pidfs_dentry_operations = {
+ .d_dname = pidfs_dname,
+ .d_prune = stashed_dentry_prune,
+};
+
+static int pidfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
+ struct inode *parent)
+{
+ const struct pid *pid = inode->i_private;
+
+ if (*max_len < 2) {
+ *max_len = 2;
+ return FILEID_INVALID;
+ }
+
+ *max_len = 2;
+ *(u64 *)fh = pid->ino;
+ return FILEID_KERNFS;
+}
+
+static int pidfs_ino_find(const void *key, const struct rb_node *node)
+{
+ const u64 pid_ino = *(u64 *)key;
+ const struct pid *pid = rb_entry(node, struct pid, pidfs_node);
+
+ if (pid_ino < pid->ino)
+ return -1;
+ if (pid_ino > pid->ino)
+ return 1;
+ return 0;
+}
+
+/* Find a struct pid based on the inode number. */
+static struct pid *pidfs_ino_get_pid(u64 ino)
+{
+ struct pid *pid;
+ struct rb_node *node;
+ unsigned int seq;
+
+ guard(rcu)();
+ do {
+ seq = read_seqcount_begin(&pidmap_lock_seq);
+ node = rb_find_rcu(&ino, &pidfs_ino_tree, pidfs_ino_find);
+ if (node)
+ break;
+ } while (read_seqcount_retry(&pidmap_lock_seq, seq));
+
+ if (!node)
+ return NULL;
+
+ pid = rb_entry(node, struct pid, pidfs_node);
+
+ /* Within our pid namespace hierarchy? */
+ if (pid_vnr(pid) == 0)
+ return NULL;
+
+ return get_pid(pid);
+}
+
+static struct dentry *pidfs_fh_to_dentry(struct super_block *sb,
+ struct fid *fid, int fh_len,
+ int fh_type)
+{
+ int ret;
+ u64 pid_ino;
+ struct path path;
+ struct pid *pid;
+
+ if (fh_len < 2)
+ return NULL;
+
+ switch (fh_type) {
+ case FILEID_KERNFS:
+ pid_ino = *(u64 *)fid;
+ break;
+ default:
+ return NULL;
+ }
+
+ pid = pidfs_ino_get_pid(pid_ino);
+ if (!pid)
+ return NULL;
+
+ ret = path_from_stashed(&pid->stashed, pidfs_mnt, pid, &path);
+ if (ret < 0)
+ return ERR_PTR(ret);
+
+ VFS_WARN_ON_ONCE(!pid->attr);
+
+ mntput(path.mnt);
+ return path.dentry;
+}
+
+/*
+ * Make sure that we reject any nonsensical flags that users pass via
+ * open_by_handle_at(). Note that PIDFD_THREAD is defined as O_EXCL, and
+ * PIDFD_NONBLOCK as O_NONBLOCK.
+ */
+#define VALID_FILE_HANDLE_OPEN_FLAGS \
+ (O_RDONLY | O_WRONLY | O_RDWR | O_NONBLOCK | O_CLOEXEC | O_EXCL)
+
+static int pidfs_export_permission(struct handle_to_path_ctx *ctx,
+ unsigned int oflags)
+{
+ if (oflags & ~(VALID_FILE_HANDLE_OPEN_FLAGS | O_LARGEFILE))
+ return -EINVAL;
+
+ /*
+ * pidfd_ino_get_pid() will verify that the struct pid is part
+ * of the caller's pid namespace hierarchy. No further
+ * permission checks are needed.
+ */
+ return 0;
+}
+
+static struct file *pidfs_export_open(const struct path *path, unsigned int oflags)
+{
+ /*
+ * Clear O_LARGEFILE as open_by_handle_at() forces it and raise
+ * O_RDWR as pidfds always are.
+ */
+ oflags &= ~O_LARGEFILE;
+ return dentry_open(path, oflags | O_RDWR, current_cred());
+}
+
+static const struct export_operations pidfs_export_operations = {
+ .encode_fh = pidfs_encode_fh,
+ .fh_to_dentry = pidfs_fh_to_dentry,
+ .open = pidfs_export_open,
+ .permission = pidfs_export_permission,
+};
+
+static int pidfs_init_inode(struct inode *inode, void *data)
+{
+ const struct pid *pid = data;
+
+ inode->i_private = data;
+ inode->i_flags |= S_PRIVATE | S_ANON_INODE;
+ /* We allow to set xattrs. */
+ inode->i_flags &= ~S_IMMUTABLE;
+ inode->i_mode |= S_IRWXU;
+ inode->i_op = &pidfs_inode_operations;
+ inode->i_fop = &pidfs_file_operations;
+ inode->i_ino = pidfs_ino(pid->ino);
+ inode->i_generation = pidfs_gen(pid->ino);
+ return 0;
+}
+
+static void pidfs_put_data(void *data)
+{
+ struct pid *pid = data;
+ put_pid(pid);
+}
+
+/**
+ * pidfs_register_pid - register a struct pid in pidfs
+ * @pid: pid to pin
+ *
+ * Register a struct pid in pidfs.
+ *
+ * Return: On success zero, on error a negative error code is returned.
+ */
+int pidfs_register_pid(struct pid *pid)
+{
+ struct pidfs_attr *new_attr __free(kfree) = NULL;
+ struct pidfs_attr *attr;
+
+ might_sleep();
+
+ if (!pid)
+ return 0;
+
+ attr = READ_ONCE(pid->attr);
+ if (unlikely(attr == PIDFS_PID_DEAD))
+ return PTR_ERR(PIDFS_PID_DEAD);
+ if (attr)
+ return 0;
+
+ new_attr = kmem_cache_zalloc(pidfs_attr_cachep, GFP_KERNEL);
+ if (!new_attr)
+ return -ENOMEM;
+
+ /* Synchronize with pidfs_exit(). */
+ guard(spinlock_irq)(&pid->wait_pidfd.lock);
+
+ attr = pid->attr;
+ if (unlikely(attr == PIDFS_PID_DEAD))
+ return PTR_ERR(PIDFS_PID_DEAD);
+ if (unlikely(attr))
+ return 0;
+
+ pid->attr = no_free_ptr(new_attr);
+ return 0;
+}
+
+static struct dentry *pidfs_stash_dentry(struct dentry **stashed,
+ struct dentry *dentry)
+{
+ int ret;
+ struct pid *pid = d_inode(dentry)->i_private;
+
+ VFS_WARN_ON_ONCE(stashed != &pid->stashed);
+
+ ret = pidfs_register_pid(pid);
+ if (ret)
+ return ERR_PTR(ret);
+
+ return stash_dentry(stashed, dentry);
+}
+
+static const struct stashed_operations pidfs_stashed_ops = {
+ .stash_dentry = pidfs_stash_dentry,
+ .init_inode = pidfs_init_inode,
+ .put_data = pidfs_put_data,
+};
+
+static int pidfs_xattr_get(const struct xattr_handler *handler,
+ struct dentry *unused, struct inode *inode,
+ const char *suffix, void *value, size_t size)
+{
+ struct pid *pid = inode->i_private;
+ struct pidfs_attr *attr = pid->attr;
+ const char *name;
+ struct simple_xattrs *xattrs;
+
+ xattrs = READ_ONCE(attr->xattrs);
+ if (!xattrs)
+ return 0;
+
+ name = xattr_full_name(handler, suffix);
+ return simple_xattr_get(xattrs, name, value, size);
+}
+
+static int pidfs_xattr_set(const struct xattr_handler *handler,
+ struct mnt_idmap *idmap, struct dentry *unused,
+ struct inode *inode, const char *suffix,
+ const void *value, size_t size, int flags)
+{
+ struct pid *pid = inode->i_private;
+ struct pidfs_attr *attr = pid->attr;
+ const char *name;
+ struct simple_xattrs *xattrs;
+ struct simple_xattr *old_xattr;
+
+ /* Ensure we're the only one to set @attr->xattrs. */
+ WARN_ON_ONCE(!inode_is_locked(inode));
+
+ xattrs = READ_ONCE(attr->xattrs);
+ if (!xattrs) {
+ xattrs = kmem_cache_zalloc(pidfs_xattr_cachep, GFP_KERNEL);
+ if (!xattrs)
+ return -ENOMEM;
+
+ simple_xattrs_init(xattrs);
+ smp_store_release(&pid->attr->xattrs, xattrs);
+ }
+
+ name = xattr_full_name(handler, suffix);
+ old_xattr = simple_xattr_set(xattrs, name, value, size, flags);
+ if (IS_ERR(old_xattr))
+ return PTR_ERR(old_xattr);
+
+ simple_xattr_free(old_xattr);
+ return 0;
+}
+
+static const struct xattr_handler pidfs_trusted_xattr_handler = {
+ .prefix = XATTR_TRUSTED_PREFIX,
+ .get = pidfs_xattr_get,
+ .set = pidfs_xattr_set,
+};
+
+static const struct xattr_handler *const pidfs_xattr_handlers[] = {
+ &pidfs_trusted_xattr_handler,
+ NULL
+};
+
+static int pidfs_init_fs_context(struct fs_context *fc)
+{
+ struct pseudo_fs_context *ctx;
+
+ ctx = init_pseudo(fc, PID_FS_MAGIC);
+ if (!ctx)
+ return -ENOMEM;
+
+ fc->s_iflags |= SB_I_NOEXEC;
+ fc->s_iflags |= SB_I_NODEV;
+ ctx->s_d_flags |= DCACHE_DONTCACHE;
+ ctx->ops = &pidfs_sops;
+ ctx->eops = &pidfs_export_operations;
+ ctx->dops = &pidfs_dentry_operations;
+ ctx->xattr = pidfs_xattr_handlers;
+ fc->s_fs_info = (void *)&pidfs_stashed_ops;
+ return 0;
+}
+
+static struct file_system_type pidfs_type = {
+ .name = "pidfs",
+ .init_fs_context = pidfs_init_fs_context,
+ .kill_sb = kill_anon_super,
+};
+
+struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
+{
+ struct file *pidfd_file;
+ struct path path __free(path_put) = {};
+ int ret;
+
+ /*
+ * Ensure that PIDFD_STALE can be passed as a flag without
+ * overloading other uapi pidfd flags.
+ */
+ BUILD_BUG_ON(PIDFD_STALE == PIDFD_THREAD);
+ BUILD_BUG_ON(PIDFD_STALE == PIDFD_NONBLOCK);
+
+ ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path);
+ if (ret < 0)
+ return ERR_PTR(ret);
+
+ VFS_WARN_ON_ONCE(!pid->attr);
+
+ flags &= ~PIDFD_STALE;
+ flags |= O_RDWR;
+ pidfd_file = dentry_open(&path, flags, current_cred());
+ /* Raise PIDFD_THREAD explicitly as do_dentry_open() strips it. */
+ if (!IS_ERR(pidfd_file))
+ pidfd_file->f_flags |= (flags & PIDFD_THREAD);
+
+ return pidfd_file;
+}
+
+void __init pidfs_init(void)
+{
+ pidfs_attr_cachep = kmem_cache_create("pidfs_attr_cache", sizeof(struct pidfs_attr), 0,
+ (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
+ SLAB_ACCOUNT | SLAB_PANIC), NULL);
+
+ pidfs_xattr_cachep = kmem_cache_create("pidfs_xattr_cache",
+ sizeof(struct simple_xattrs), 0,
+ (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
+ SLAB_ACCOUNT | SLAB_PANIC), NULL);
+
+ pidfs_mnt = kern_mount(&pidfs_type);
+ if (IS_ERR(pidfs_mnt))
+ panic("Failed to mount pidfs pseudo filesystem");
+
+ pidfs_root_path.mnt = pidfs_mnt;
+ pidfs_root_path.dentry = pidfs_mnt->mnt_root;
+}
generated by cgit (git 2.34.1) at 2025-12-21 21:12:36 +0000