diff options
Diffstat (limited to 'chromium/sandbox/linux/suid/linux_util.c')
-rw-r--r-- | chromium/sandbox/linux/suid/linux_util.c | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/chromium/sandbox/linux/suid/linux_util.c b/chromium/sandbox/linux/suid/linux_util.c new file mode 100644 index 00000000000..256468ff4ea --- /dev/null +++ b/chromium/sandbox/linux/suid/linux_util.c @@ -0,0 +1,135 @@ +// 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; +} |