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// Copyright (c) 2009 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// The following is duplicated from base/linux_utils.cc.
// We shouldn't link against C++ code in a setuid binary.
#define _GNU_SOURCE // For O_DIRECTORY
#include "linux_util.h"
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
// expected prefix of the target of the /proc/self/fd/%d link for a socket
static const char kSocketLinkPrefix[] = "socket:[";
// Parse a symlink in /proc/pid/fd/$x and return the inode number of the
// socket.
// inode_out: (output) set to the inode number on success
// path: e.g. /proc/1234/fd/5 (must be a UNIX domain socket descriptor)
static bool ProcPathGetInodeAt(ino_t* inode_out, int base_dir_fd,
const char* path) {
// We also check that the path is relative.
if (!inode_out || !path || *path == '/')
return false;
char buf[256];
const ssize_t n = readlinkat(base_dir_fd, path, buf, sizeof(buf) - 1);
if (n < 0)
return false;
buf[n] = 0;
if (memcmp(kSocketLinkPrefix, buf, sizeof(kSocketLinkPrefix) - 1))
return false;
char *endptr = NULL;
errno = 0;
const unsigned long long int inode_ull =
strtoull(buf + sizeof(kSocketLinkPrefix) - 1, &endptr, 10);
if (inode_ull == ULLONG_MAX || !endptr || *endptr != ']' || errno != 0)
return false;
*inode_out = inode_ull;
return true;
}
static DIR* opendirat(int base_dir_fd, const char* name) {
// Also check that |name| is relative.
if (base_dir_fd < 0 || !name || *name == '/')
return NULL;
int new_dir_fd = openat(base_dir_fd, name, O_RDONLY | O_DIRECTORY);
if (new_dir_fd < 0)
return NULL;
return fdopendir(new_dir_fd);
}
bool FindProcessHoldingSocket(pid_t* pid_out, ino_t socket_inode) {
bool already_found = false;
DIR* proc = opendir("/proc");
if (!proc)
return false;
const uid_t uid = getuid();
struct dirent* dent;
while ((dent = readdir(proc))) {
char *endptr = NULL;
errno = 0;
const unsigned long int pid_ul = strtoul(dent->d_name, &endptr, 10);
if (pid_ul == ULONG_MAX || !endptr || *endptr || errno != 0)
continue;
// We have this setuid code here because the zygote and its children have
// /proc/$pid/fd owned by root. While scanning through /proc, we add this
// extra check so users cannot accidentally gain information about other
// users' processes. To determine process ownership, we use the property
// that if user foo owns process N, then /proc/N is owned by foo.
int proc_pid_fd = -1;
{
char buf[256];
struct stat statbuf;
snprintf(buf, sizeof(buf), "/proc/%lu", pid_ul);
proc_pid_fd = open(buf, O_RDONLY | O_DIRECTORY);
if (proc_pid_fd < 0)
continue;
if (fstat(proc_pid_fd, &statbuf) < 0 || uid != statbuf.st_uid) {
close(proc_pid_fd);
continue;
}
}
DIR* fd = opendirat(proc_pid_fd, "fd");
if (!fd) {
close(proc_pid_fd);
continue;
}
while ((dent = readdir(fd))) {
char buf[256];
int printed = snprintf(buf, sizeof(buf), "fd/%s", dent->d_name);
if (printed < 0 || printed >= (int)(sizeof(buf) - 1)) {
continue;
}
ino_t fd_inode;
if (ProcPathGetInodeAt(&fd_inode, proc_pid_fd, buf)) {
if (fd_inode == socket_inode) {
if (already_found) {
closedir(fd);
close(proc_pid_fd);
closedir(proc);
return false;
}
already_found = true;
*pid_out = pid_ul;
break;
}
}
}
closedir(fd);
close(proc_pid_fd);
}
closedir(proc);
return already_found;
}
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