LXR linux/net/unix/scm.c

   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/module.h>
   3#include <linux/kernel.h>
   4#include <linux/string.h>
   5#include <linux/socket.h>
   6#include <linux/net.h>
   7#include <linux/fs.h>
   8#include <net/af_unix.h>
   9#include <net/scm.h>
  10#include <linux/init.h>
  11#include <linux/io_uring.h>
  12
  13#include "scm.h"
  14
  15unsigned int unix_tot_inflight;
  16EXPORT_SYMBOL(unix_tot_inflight);
  17
  18LIST_HEAD(gc_inflight_list);
  19EXPORT_SYMBOL(gc_inflight_list);
  20
  21DEFINE_SPINLOCK(unix_gc_lock);
  22EXPORT_SYMBOL(unix_gc_lock);
  23
  24struct sock *unix_get_socket(struct file *filp)
  25{
  26        struct sock *u_sock = NULL;
  27        struct inode *inode = file_inode(filp);
  28
  29        /* Socket ? */
  30        if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
  31                struct socket *sock = SOCKET_I(inode);
  32                struct sock *s = sock->sk;
  33
  34                /* PF_UNIX ? */
  35                if (s && sock->ops && sock->ops->family == PF_UNIX)
  36                        u_sock = s;
  37        } else {
  38                /* Could be an io_uring instance */
  39                u_sock = io_uring_get_socket(filp);
  40        }
  41        return u_sock;
  42}
  43EXPORT_SYMBOL(unix_get_socket);
  44
  45/* Keep the number of times in flight count for the file
  46 * descriptor if it is for an AF_UNIX socket.
  47 */
  48void unix_inflight(struct user_struct *user, struct file *fp)
  49{
  50        struct sock *s = unix_get_socket(fp);
  51
  52        spin_lock(&unix_gc_lock);
  53
  54        if (s) {
  55                struct unix_sock *u = unix_sk(s);
  56
  57                if (atomic_long_inc_return(&u->inflight) == 1) {
  58                        BUG_ON(!list_empty(&u->link));
  59                        list_add_tail(&u->link, &gc_inflight_list);
  60                } else {
  61                        BUG_ON(list_empty(&u->link));
  62                }
  63                unix_tot_inflight++;
  64        }
  65        user->unix_inflight++;
  66        spin_unlock(&unix_gc_lock);
  67}
  68
  69void unix_notinflight(struct user_struct *user, struct file *fp)
  70{
  71        struct sock *s = unix_get_socket(fp);
  72
  73        spin_lock(&unix_gc_lock);
  74
  75        if (s) {
  76                struct unix_sock *u = unix_sk(s);
  77
  78                BUG_ON(!atomic_long_read(&u->inflight));
  79                BUG_ON(list_empty(&u->link));
  80
  81                if (atomic_long_dec_and_test(&u->inflight))
  82                        list_del_init(&u->link);
  83                unix_tot_inflight--;
  84        }
  85        user->unix_inflight--;
  86        spin_unlock(&unix_gc_lock);
  87}
  88
  89/*
  90 * The "user->unix_inflight" variable is protected by the garbage
  91 * collection lock, and we just read it locklessly here. If you go
  92 * over the limit, there might be a tiny race in actually noticing
  93 * it across threads. Tough.
  94 */
  95static inline bool too_many_unix_fds(struct task_struct *p)
  96{
  97        struct user_struct *user = current_user();
  98
  99        if (unlikely(user->unix_inflight > task_rlimit(p, RLIMIT_NOFILE)))
 100                return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
 101        return false;
 102}
 103
 104int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
 105{
 106        int i;
 107
 108        if (too_many_unix_fds(current))
 109                return -ETOOMANYREFS;
 110
 111        /*
 112         * Need to duplicate file references for the sake of garbage
 113         * collection.  Otherwise a socket in the fps might become a
 114         * candidate for GC while the skb is not yet queued.
 115         */
 116        UNIXCB(skb).fp = scm_fp_dup(scm->fp);
 117        if (!UNIXCB(skb).fp)
 118                return -ENOMEM;
 119
 120        for (i = scm->fp->count - 1; i >= 0; i--)
 121                unix_inflight(scm->fp->user, scm->fp->fp[i]);
 122        return 0;
 123}
 124EXPORT_SYMBOL(unix_attach_fds);
 125
 126void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
 127{
 128        int i;
 129
 130        scm->fp = UNIXCB(skb).fp;
 131        UNIXCB(skb).fp = NULL;
 132
 133        for (i = scm->fp->count-1; i >= 0; i--)
 134                unix_notinflight(scm->fp->user, scm->fp->fp[i]);
 135}
 136EXPORT_SYMBOL(unix_detach_fds);
 137
 138void unix_destruct_scm(struct sk_buff *skb)
 139{
 140        struct scm_cookie scm;
 141
 142        memset(&scm, 0, sizeof(scm));
 143        scm.pid  = UNIXCB(skb).pid;
 144        if (UNIXCB(skb).fp)
 145                unix_detach_fds(&scm, skb);
 146
 147        /* Alas, it calls VFS */
 148        /* So fscking what? fput() had been SMP-safe since the last Summer */
 149        scm_destroy(&scm);
 150        sock_wfree(skb);
 151}
 152EXPORT_SYMBOL(unix_destruct_scm);
 153