fs/proc/self.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/cache.h>
   3 #include <linux/sched.h>
   4 #include <linux/slab.h>
   5 #include <linux/pid_namespace.h>
   6 #include "internal.h"
   7
   8 /*
   9  * /proc/self:
  10  */
  11 static const char *proc_self_get_link(struct dentry *dentry,
  12                                       struct inode *inode,
  13                                       struct delayed_call *done)
  14 {
  15         struct pid_namespace *ns = proc_pid_ns(inode);
  16         pid_t tgid = task_tgid_nr_ns(current, ns);
  17         char *name;
  18
  19         if (!tgid)
  20                 return ERR_PTR(-ENOENT);
  21         /* max length of unsigned int in decimal + NULL term */
  22         name = kmalloc(10 + 1, dentry ? GFP_KERNEL : GFP_ATOMIC);
  23         if (unlikely(!name))
  24                 return dentry ? ERR_PTR(-ENOMEM) : ERR_PTR(-ECHILD);
  25         sprintf(name, "%u", tgid);
  26         set_delayed_call(done, kfree_link, name);
  27         return name;
  28 }
  29
  30 static const struct inode_operations proc_self_inode_operations = {
  31         .get_link       = proc_self_get_link,
  32 };
  33
  34 static unsigned self_inum __ro_after_init;
  35
  36 int proc_setup_self(struct super_block *s)
  37 {
  38         struct inode *root_inode = d_inode(s->s_root);
  39         struct pid_namespace *ns = proc_pid_ns(root_inode);
  40         struct dentry *self;
  41         int ret = -ENOMEM;
  42
  43         inode_lock(root_inode);
  44         self = d_alloc_name(s->s_root, "self");
  45         if (self) {
  46                 struct inode *inode = new_inode(s);
  47                 if (inode) {
  48                         inode->i_ino = self_inum;
  49                         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  50                         inode->i_mode = S_IFLNK | S_IRWXUGO;
  51                         inode->i_uid = GLOBAL_ROOT_UID;
  52                         inode->i_gid = GLOBAL_ROOT_GID;
  53                         inode->i_op = &proc_self_inode_operations;
  54                         d_add(self, inode);
  55                         ret = 0;
  56                 } else {
  57                         dput(self);
  58                 }
  59         }
  60         inode_unlock(root_inode);
  61
  62         if (ret)
  63                 pr_err("proc_fill_super: can't allocate /proc/self\n");
  64         else
  65                 ns->proc_self = self;
  66
  67         return ret;
  68 }
  69
  70 void __init proc_self_init(void)
  71 {
  72         proc_alloc_inum(&self_inum);
  73 }