1 // Copyright (c) 2009 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // The following is duplicated from base/linux_utils.cc. 6 // We shouldn't link against C++ code in a setuid binary. 7 8 // Needed for O_DIRECTORY, must be defined before fcntl.h is included 9 // (and it can be included earlier than the explicit #include below 10 // in some versions of glibc). 11 #define _GNU_SOURCE 12 13 #include "sandbox/linux/suid/linux_util.h" 14 15 #include <dirent.h> 16 #include <errno.h> 17 #include <fcntl.h> 18 #include <limits.h> 19 #include <stdio.h> 20 #include <stdlib.h> 21 #include <string.h> 22 #include <sys/stat.h> 23 #include <sys/types.h> 24 #include <unistd.h> 25 26 // expected prefix of the target of the /proc/self/fd/%d link for a socket 27 static const char kSocketLinkPrefix[] = "socket:["; 28 29 // Parse a symlink in /proc/pid/fd/$x and return the inode number of the 30 // socket. 31 // inode_out: (output) set to the inode number on success 32 // path: e.g. /proc/1234/fd/5 (must be a UNIX domain socket descriptor) 33 static bool ProcPathGetInodeAt(ino_t* inode_out, 34 int base_dir_fd, 35 const char* path) { 36 // We also check that the path is relative. 37 if (!inode_out || !path || *path == '/') 38 return false; 39 char buf[256]; 40 const ssize_t n = readlinkat(base_dir_fd, path, buf, sizeof(buf) - 1); 41 if (n < 0) 42 return false; 43 buf[n] = 0; 44 45 if (memcmp(kSocketLinkPrefix, buf, sizeof(kSocketLinkPrefix) - 1)) 46 return false; 47 48 char* endptr = NULL; 49 errno = 0; 50 const unsigned long long int inode_ull = 51 strtoull(buf + sizeof(kSocketLinkPrefix) - 1, &endptr, 10); 52 if (inode_ull == ULLONG_MAX || !endptr || *endptr != ']' || errno != 0) 53 return false; 54 55 *inode_out = inode_ull; 56 return true; 57 } 58 59 static DIR* opendirat(int base_dir_fd, const char* name) { 60 // Also check that |name| is relative. 61 if (base_dir_fd < 0 || !name || *name == '/') 62 return NULL; 63 int new_dir_fd = openat(base_dir_fd, name, O_RDONLY | O_DIRECTORY); 64 if (new_dir_fd < 0) 65 return NULL; 66 67 return fdopendir(new_dir_fd); 68 } 69 70 bool FindProcessHoldingSocket(pid_t* pid_out, ino_t socket_inode) { 71 bool already_found = false; 72 73 DIR* proc = opendir("/proc"); 74 if (!proc) 75 return false; 76 77 const uid_t uid = getuid(); 78 struct dirent* dent; 79 while ((dent = readdir(proc))) { 80 char* endptr = NULL; 81 errno = 0; 82 const unsigned long int pid_ul = strtoul(dent->d_name, &endptr, 10); 83 if (pid_ul == ULONG_MAX || !endptr || *endptr || errno != 0) 84 continue; 85 86 // We have this setuid code here because the zygote and its children have 87 // /proc/$pid/fd owned by root. While scanning through /proc, we add this 88 // extra check so users cannot accidentally gain information about other 89 // users' processes. To determine process ownership, we use the property 90 // that if user foo owns process N, then /proc/N is owned by foo. 91 int proc_pid_fd = -1; 92 { 93 char buf[256]; 94 struct stat statbuf; 95 snprintf(buf, sizeof(buf), "/proc/%lu", pid_ul); 96 proc_pid_fd = open(buf, O_RDONLY | O_DIRECTORY); 97 if (proc_pid_fd < 0) 98 continue; 99 if (fstat(proc_pid_fd, &statbuf) < 0 || uid != statbuf.st_uid) { 100 close(proc_pid_fd); 101 continue; 102 } 103 } 104 105 DIR* fd = opendirat(proc_pid_fd, "fd"); 106 if (!fd) { 107 close(proc_pid_fd); 108 continue; 109 } 110 111 while ((dent = readdir(fd))) { 112 char buf[256]; 113 int printed = snprintf(buf, sizeof(buf), "fd/%s", dent->d_name); 114 if (printed < 0 || printed >= (int)(sizeof(buf) - 1)) { 115 continue; 116 } 117 118 ino_t fd_inode; 119 if (ProcPathGetInodeAt(&fd_inode, proc_pid_fd, buf)) { 120 if (fd_inode == socket_inode) { 121 if (already_found) { 122 closedir(fd); 123 close(proc_pid_fd); 124 closedir(proc); 125 return false; 126 } 127 128 already_found = true; 129 *pid_out = pid_ul; 130 break; 131 } 132 } 133 } 134 closedir(fd); 135 close(proc_pid_fd); 136 } 137 closedir(proc); 138 139 return already_found; 140 } 141
