From c166890023f56388cb3482cff3def04171a488c4 Mon Sep 17 00:00:00 2001 From: "Heiko Schlittermann (HS12-RIPE)" Date: Thu, 25 Mar 2021 22:48:09 +0100 Subject: [PATCH 26/29] CVE-2020-28014, CVE-2021-27216: Arbitrary PID file creation, clobbering, and deletion Arbitrary PID file creation, clobbering, and deletion. Patch provided by Qualys. (cherry picked from commit 974f32939a922512b27d9f0a8a1cb5dec60e7d37) (cherry picked from commit 43c6f0b83200b7082353c50187ef75de3704580a) --- doc/ChangeLog | 5 + src/daemon.c | 212 ++++++++++++++++++++++++++++++++++++++---- src/exim.c | 12 ++- test/stderr/0433 | 24 +++++ 4 files changed, 232 insertions(+), 21 deletions(-) --- a/doc/ChangeLog +++ b/doc/ChangeLog @@ -10,13 +10,18 @@ QS/02 PID file creation/deletion: only p runtime user. QS/01 Creation of (database) files in $spool_dir: only uid=0 or the euid of the Exim runtime user are allowed to create files. +QS/01 Creation of (database) files in $spool_dir: only uid=0 or the uid of + the Exim runtime user are allowed to create files. HS/01 Handle trailing backslash gracefully. (CVE-2019-15846) +QS/02 PID file creation/deletion: only possible if uid=0 or uid is the Exim + runtime user. + Since version 4.92 ------------------ JH/06 Fix buggy handling of autoreply bounce_return_size_limit, and a possible --- a/src/daemon.c +++ b/src/daemon.c @@ -886,10 +886,198 @@ while ((pid = waitpid(-1, &status, WNOHA } } } +static void +set_pid_file_path(void) +{ +if (override_pid_file_path) + pid_file_path = override_pid_file_path; + +if (!*pid_file_path) + pid_file_path = string_sprintf("%s/exim-daemon.pid", spool_directory); + +if (pid_file_path[0] != '/') + log_write(0, LOG_PANIC_DIE, "pid file path %s must be absolute\n", pid_file_path); +} + + +enum pid_op { PID_WRITE, PID_CHECK, PID_DELETE }; + +/* Do various pid file operations as safe as possible. Ideally we'd just +drop the privileges for creation of the pid file and not care at all about removal of +the file. FIXME. +Returns: true on success, false + errno==EACCES otherwise +*/ +static BOOL +operate_on_pid_file(const enum pid_op operation, const pid_t pid) +{ +char pid_line[sizeof(int) * 3 + 2]; +const int pid_len = snprintf(pid_line, sizeof(pid_line), "%d\n", (int)pid); +BOOL lines_match = FALSE; + +char * path = NULL; +char * base = NULL; +char * dir = NULL; + +const int dir_flags = O_RDONLY | O_NONBLOCK; +const int base_flags = O_NOFOLLOW | O_NONBLOCK; +const mode_t base_mode = 0644; +struct stat sb; + +int cwd_fd = -1; +int dir_fd = -1; +int base_fd = -1; + +BOOL success = FALSE; +errno = EACCES; + +set_pid_file_path(); +if (!f.running_in_test_harness && real_uid != root_uid && real_uid != exim_uid) goto cleanup; +if (pid_len < 2 || pid_len >= (int)sizeof(pid_line)) goto cleanup; + +path = CS string_copy(pid_file_path); +if ((base = Ustrrchr(path, '/')) == NULL) /* should not happen, but who knows */ + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "pid file path \"%s\" does not contain a '/'", pid_file_path); + +dir = (base != path) ? path : "/"; +*base++ = '\0'; + +if (!dir || !*dir || *dir != '/') goto cleanup; +if (!base || !*base || strchr(base, '/') != NULL) goto cleanup; + +cwd_fd = open(".", dir_flags); +if (cwd_fd < 0 || fstat(cwd_fd, &sb) != 0 || !S_ISDIR(sb.st_mode)) goto cleanup; +dir_fd = open(dir, dir_flags); +if (dir_fd < 0 || fstat(dir_fd, &sb) != 0 || !S_ISDIR(sb.st_mode)) goto cleanup; + +/* emulate openat */ +if (fchdir(dir_fd) != 0) goto cleanup; +base_fd = open(base, O_RDONLY | base_flags); +if (fchdir(cwd_fd) != 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "can't return to previous working dir: %s", strerror(errno)); + +if (base_fd >= 0) + { + char line[sizeof(pid_line)]; + ssize_t len = -1; + + if (fstat(base_fd, &sb) != 0 || !S_ISREG(sb.st_mode)) goto cleanup; + if ((sb.st_mode & 07777) != base_mode || sb.st_nlink != 1) goto cleanup; + if (sb.st_size < 2 || sb.st_size >= (off_t)sizeof(line)) goto cleanup; + + len = read(base_fd, line, sizeof(line)); + if (len != (ssize_t)sb.st_size) goto cleanup; + line[len] = '\0'; + + if (strspn(line, "0123456789") != (size_t)len-1) goto cleanup; + if (line[len-1] != '\n') goto cleanup; + lines_match = (len == pid_len && strcmp(line, pid_line) == 0); + } + +if (operation == PID_WRITE) + { + if (!lines_match) + { + if (base_fd >= 0) + { + int error = -1; + /* emulate unlinkat */ + if (fchdir(dir_fd) != 0) goto cleanup; + error = unlink(base); + if (fchdir(cwd_fd) != 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "can't return to previous working dir: %s", strerror(errno)); + if (error) goto cleanup; + (void)close(base_fd); + base_fd = -1; + } + /* emulate openat */ + if (fchdir(dir_fd) != 0) goto cleanup; + base_fd = open(base, O_WRONLY | O_CREAT | O_EXCL | base_flags, base_mode); + if (fchdir(cwd_fd) != 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "can't return to previous working dir: %s", strerror(errno)); + if (base_fd < 0) goto cleanup; + if (fchmod(base_fd, base_mode) != 0) goto cleanup; + if (write(base_fd, pid_line, pid_len) != pid_len) goto cleanup; + DEBUG(D_any) debug_printf("pid written to %s\n", pid_file_path); + } + } +else + { + if (!lines_match) goto cleanup; + if (operation == PID_DELETE) + { + int error = -1; + /* emulate unlinkat */ + if (fchdir(dir_fd) != 0) goto cleanup; + error = unlink(base); + if (fchdir(cwd_fd) != 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "can't return to previous working dir: %s", strerror(errno)); + if (error) goto cleanup; + } + } + +success = TRUE; +errno = 0; + +cleanup: +if (cwd_fd >= 0) (void)close(cwd_fd); +if (dir_fd >= 0) (void)close(dir_fd); +if (base_fd >= 0) (void)close(base_fd); +return success; +} + + +/* Remove the daemon's pidfile. Note: runs with root privilege, +as a direct child of the daemon. Does not return. */ + +void +delete_pid_file(void) +{ +const BOOL success = operate_on_pid_file(PID_DELETE, getppid()); + +DEBUG(D_any) + debug_printf("delete pid file %s %s: %s\n", pid_file_path, + success ? "success" : "failure", strerror(errno)); + +exim_exit(EXIT_SUCCESS, US""); +} + + +/* Called by the daemon; exec a child to get the pid file deleted +since we may require privs for the containing directory */ + +static void +daemon_die(void) +{ +int pid; + +DEBUG(D_any) debug_printf("SIGTERM/SIGINT seen\n"); +#if defined(SUPPORT_TLS) && (defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)) +tls_watch_invalidate(); +#endif + +if (f.running_in_test_harness || write_pid) + { + if ((pid = fork()) == 0) + { + if (override_pid_file_path) + (void)child_exec_exim(CEE_EXEC_PANIC, FALSE, NULL, FALSE, 3, + "-oP", override_pid_file_path, "-oPX"); + else + (void)child_exec_exim(CEE_EXEC_PANIC, FALSE, NULL, FALSE, 1, "-oPX"); + + /* Control never returns here. */ + } + if (pid > 0) + child_close(pid, 1); + } +exim_exit(EXIT_SUCCESS, US""); +} + + /************************************************* * Exim Daemon Mainline * *************************************************/ @@ -1538,32 +1726,18 @@ automatically. Consequently, Exim 4 writ The variable daemon_write_pid is used to control this. */ if (f.running_in_test_harness || write_pid) { - FILE *f; - - if (override_pid_file_path) - pid_file_path = override_pid_file_path; - - if (pid_file_path[0] == 0) - pid_file_path = string_sprintf("%s/exim-daemon.pid", spool_directory); - - if ((f = modefopen(pid_file_path, "wb", 0644))) - { - (void)fprintf(f, "%d\n", (int)getpid()); - (void)fclose(f); - DEBUG(D_any) debug_printf("pid written to %s\n", pid_file_path); - } - else - DEBUG(D_any) - debug_printf("%s\n", string_open_failed(errno, "pid file %s", - pid_file_path)); + const enum pid_op operation = (f.running_in_test_harness + || real_uid == root_uid + || (real_uid == exim_uid && !override_pid_file_path)) ? PID_WRITE : PID_CHECK; + if (!operate_on_pid_file(operation, getpid())) + DEBUG(D_any) debug_printf("%s pid file %s: %s\n", (operation == PID_WRITE) ? "write" : "check", pid_file_path, strerror(errno)); } /* Set up the handler for SIGHUP, which causes a restart of the daemon. */ - sighup_seen = FALSE; signal(SIGHUP, sighup_handler); /* Give up root privilege at this point (assuming that exim_uid and exim_gid are not root). The third argument controls the running of initgroups(). --- a/src/exim.c +++ b/src/exim.c @@ -3042,12 +3042,20 @@ for (i = 1; i < argc; i++) else if (Ustrcmp(argrest, "o") == 0) {} /* -oP : set pid file path for daemon */ - else if (Ustrcmp(argrest, "P") == 0) - override_pid_file_path = argv[++i]; + else if (*argrest == 'P') + { + if (!f.running_in_test_harness && real_uid != root_uid && real_uid != exim_uid) + exim_fail("exim: only uid=%d or uid=%d can use -oP and -oPX " + "(uid=%d euid=%d | %d)\n", + root_uid, exim_uid, getuid(), geteuid(), real_uid); + if (Ustrcmp(argrest, "P") == 0) override_pid_file_path = argv[++i]; + else if (Ustrcmp(argrest, "PX") == 0) delete_pid_file(); + else badarg = TRUE; + } /* -or : set timeout for non-SMTP acceptance -os : set timeout for SMTP acceptance */ else if (*argrest == 'r' || *argrest == 's')