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         /*
  20          * Not currently supported. Once we can inherit all of struct pid,
  21          * we can allow this.
  22          */
  23         if (current->flags & PF_KTHREAD)
  24                 return ERR_PTR(-EOPNOTSUPP);
  25
  26         if (!tgid)
  27                 return ERR_PTR(-ENOENT);
  28         /* max length of unsigned int in decimal + NULL term */
  29         name = kmalloc(10 + 1, dentry ? GFP_KERNEL : GFP_ATOMIC);
  30         if (unlikely(!name))
  31                 return dentry ? ERR_PTR(-ENOMEM) : ERR_PTR(-ECHILD);
  32         sprintf(name, "%u", tgid);
  33         set_delayed_call(done, kfree_link, name);
  34         return name;
  35 }
  36
  37 static const struct inode_operations proc_self_inode_operations = {
  38         .get_link       = proc_self_get_link,
  39 };
  40
  41 static unsigned self_inum __ro_after_init;
  42
  43 int proc_setup_self(struct super_block *s)
  44 {
  45         struct inode *root_inode = d_inode(s->s_root);
  46         struct pid_namespace *ns = proc_pid_ns(root_inode);
  47         struct dentry *self;
  48
  49         inode_lock(root_inode);
  50         self = d_alloc_name(s->s_root, "self");
  51         if (self) {
  52                 struct inode *inode = new_inode(s);
  53                 if (inode) {
  54                         inode->i_ino = self_inum;
  55                         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
  56                         inode->i_mode = S_IFLNK | S_IRWXUGO;
  57                         inode->i_uid = GLOBAL_ROOT_UID;
  58                         inode->i_gid = GLOBAL_ROOT_GID;
  59                         inode->i_op = &proc_self_inode_operations;
  60                         d_add(self, inode);
  61                 } else {
  62                         dput(self);
  63                         self = ERR_PTR(-ENOMEM);
  64                 }
  65         } else {
  66                 self = ERR_PTR(-ENOMEM);
  67         }
  68         inode_unlock(root_inode);
  69         if (IS_ERR(self)) {
  70                 pr_err("proc_fill_super: can't allocate /proc/self\n");
  71                 return PTR_ERR(self);
  72         }
  73         ns->proc_self = self;
  74         return 0;
  75 }
  76
  77 void __init proc_self_init(void)
  78 {
  79         proc_alloc_inum(&self_inum);
  80 }