fs/proc/self.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/sched.h>
   3 #include <linux/slab.h>
   4 #include <linux/pid_namespace.h>
   5 #include "internal.h"
   6
   7 /*
   8  * /proc/self:
   9  */
  10 static const char *proc_self_get_link(struct dentry *dentry,
  11                                       struct inode *inode,
  12                                       struct delayed_call *done)
  13 {
  14         struct pid_namespace *ns = inode->i_sb->s_fs_info;
  15         pid_t tgid = task_tgid_nr_ns(current, ns);
  16         char *name;
  17
  18         if (!tgid)
  19                 return ERR_PTR(-ENOENT);
  20         /* 11 for max length of signed int in decimal + NULL term */
  21         name = kmalloc(12, dentry ? GFP_KERNEL : GFP_ATOMIC);
  22         if (unlikely(!name))
  23                 return dentry ? ERR_PTR(-ENOMEM) : ERR_PTR(-ECHILD);
  24         sprintf(name, "%d", tgid);
  25         set_delayed_call(done, kfree_link, name);
  26         return name;
  27 }
  28
  29 static const struct inode_operations proc_self_inode_operations = {
  30         .get_link       = proc_self_get_link,
  31 };
  32
  33 static unsigned self_inum;
  34
  35 int proc_setup_self(struct super_block *s)
  36 {
  37         struct inode *root_inode = d_inode(s->s_root);
  38         struct pid_namespace *ns = s->s_fs_info;
  39         struct dentry *self;
  40
  41         inode_lock(root_inode);
  42         self = d_alloc_name(s->s_root, "self");
  43         if (self) {
  44                 struct inode *inode = new_inode_pseudo(s);
  45                 if (inode) {
  46                         inode->i_ino = self_inum;
  47                         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  48                         inode->i_mode = S_IFLNK | S_IRWXUGO;
  49                         inode->i_uid = GLOBAL_ROOT_UID;
  50                         inode->i_gid = GLOBAL_ROOT_GID;
  51                         inode->i_op = &proc_self_inode_operations;
  52                         d_add(self, inode);
  53                 } else {
  54                         dput(self);
  55                         self = ERR_PTR(-ENOMEM);
  56                 }
  57         } else {
  58                 self = ERR_PTR(-ENOMEM);
  59         }
  60         inode_unlock(root_inode);
  61         if (IS_ERR(self)) {
  62                 pr_err("proc_fill_super: can't allocate /proc/self\n");
  63                 return PTR_ERR(self);
  64         }
  65         ns->proc_self = self;
  66         return 0;
  67 }
  68
  69 void __init proc_self_init(void)
  70 {
  71         proc_alloc_inum(&self_inum);
  72 }