1 files changed, 153 insertions, 3 deletions

diff --git a/fs/pidfs.c b/fs/pidfs.c
index eccb291862a0..6c3f010074af 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -1,9 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/anon_inodes.h>
 #include <linux/file.h>
 #include <linux/fs.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>
@@ -14,10 +16,12 @@
 
 static int pidfd_release(struct inode *inode, struct file *file)
 {
+#ifndef CONFIG_FS_PID
 	struct pid *pid = file->private_data;
 
 	file->private_data = NULL;
 	put_pid(pid);
+#endif
 	return 0;
 }
 
@@ -59,7 +63,7 @@ static int pidfd_release(struct inode *inode, struct file *file)
  */
 static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
 {
-	struct pid *pid = f->private_data;
+	struct pid *pid = pidfd_pid(f);
 	struct pid_namespace *ns;
 	pid_t nr = -1;
 
@@ -93,7 +97,7 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
  */
 static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
 {
-	struct pid *pid = file->private_data;
+	struct pid *pid = pidfd_pid(file);
 	bool thread = file->f_flags & PIDFD_THREAD;
 	struct task_struct *task;
 	__poll_t poll_flags = 0;
@@ -113,10 +117,156 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
 	return poll_flags;
 }
 
-const struct file_operations pidfd_fops = {
+static const struct file_operations pidfs_file_operations = {
 	.release	= pidfd_release,
 	.poll		= pidfd_poll,
 #ifdef CONFIG_PROC_FS
 	.show_fdinfo	= pidfd_show_fdinfo,
 #endif
 };
+
+struct pid *pidfd_pid(const struct file *file)
+{
+	if (file->f_op != &pidfs_file_operations)
+		return ERR_PTR(-EBADF);
+#ifdef CONFIG_FS_PID
+	return file_inode(file)->i_private;
+#else
+	return file->private_data;
+#endif
+}
+
+#ifdef CONFIG_FS_PID
+static struct vfsmount *pidfs_mnt __ro_after_init;
+static struct super_block *pidfs_sb __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 -EOPNOTSUPP;
+}
+
+static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
+			 struct kstat *stat, u32 request_mask,
+			 unsigned int query_flags)
+{
+	struct inode *inode = d_inode(path->dentry);
+
+	generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
+	return 0;
+}
+
+static const struct inode_operations pidfs_inode_operations = {
+	.getattr = pidfs_getattr,
+	.setattr = pidfs_setattr,
+};
+
+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	= generic_delete_inode,
+	.evict_inode	= pidfs_evict_inode,
+	.statfs		= simple_statfs,
+};
+
+static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen)
+{
+	return dynamic_dname(buffer, buflen, "pidfd:[%lu]",
+			     d_inode(dentry)->i_ino);
+}
+
+static const struct dentry_operations pidfs_dentry_operations = {
+	.d_delete	= always_delete_dentry,
+	.d_dname	= pidfs_dname,
+};
+
+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;
+
+	ctx->ops = &pidfs_sops;
+	ctx->dops = &pidfs_dentry_operations;
+	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 inode *inode;
+	struct file *pidfd_file;
+
+	inode = iget_locked(pidfs_sb, pid->ino);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	if (inode->i_state & I_NEW) {
+		/*
+		 * Inode numbering for pidfs start at RESERVED_PIDS + 1.
+		 * This avoids collisions with the root inode which is 1
+		 * for pseudo filesystems.
+		 */
+		inode->i_ino = pid->ino;
+		inode->i_mode = S_IFREG | S_IRUGO;
+		inode->i_op = &pidfs_inode_operations;
+		inode->i_fop = &pidfs_file_operations;
+		inode->i_flags |= S_IMMUTABLE;
+		inode->i_private = get_pid(pid);
+		simple_inode_init_ts(inode);
+		unlock_new_inode(inode);
+	}
+
+	pidfd_file = alloc_file_pseudo(inode, pidfs_mnt, "", flags,
+				       &pidfs_file_operations);
+	if (IS_ERR(pidfd_file))
+		iput(inode);
+
+	return pidfd_file;
+}
+
+void __init pidfs_init(void)
+{
+	pidfs_mnt = kern_mount(&pidfs_type);
+	if (IS_ERR(pidfs_mnt))
+		panic("Failed to mount pidfs pseudo filesystem");
+
+	pidfs_sb = pidfs_mnt->mnt_sb;
+}
+
+#else /* !CONFIG_FS_PID */
+
+struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
+{
+	struct file *pidfd_file;
+
+	pidfd_file = anon_inode_getfile("[pidfd]", &pidfs_file_operations, pid,
+					flags | O_RDWR);
+	if (IS_ERR(pidfd_file))
+		return pidfd_file;
+
+	get_pid(pid);
+	return pidfd_file;
+}
+
+void __init pidfs_init(void) { }
+#endif