2 * Utility functions to track file descriptors.
4 * Copyright (C) 2013-2018 Simon Ruderich
6 * This program is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
23 /* Array of tracked file descriptors. Used for fast lookups for the normally
24 * used file descriptors (0 <= fd < TRACKFDS_STATIC_COUNT). */
25 static int tracked_fds[TRACKFDS_STATIC_COUNT];
27 /* List of tracked file descriptors >= TRACKFDS_STATIC_COUNT. */
28 static int *tracked_fds_list;
29 /* Current number of items in the list. */
30 static size_t tracked_fds_list_count;
31 /* Allocated items, used to reduce realloc()s. */
32 static size_t tracked_fds_list_space;
36 static void tracked_fds_debug(void) {
39 for (i = 0; i < TRACKFDS_STATIC_COUNT; i++) {
41 debug(" tracked_fds[%d]: %d\n", i, tracked_fds[i]);
44 debug(" tracked_fds_list: %d/%d\t[%d]\n", tracked_fds_list_count,
45 tracked_fds_list_space,
47 for (i = 0; i < tracked_fds_list_count; i++) {
48 debug(" tracked_fds_list[%d]: %d\n", i, tracked_fds_list[i]);
53 /* Check if filename occurs in the comma-separated list ignore. */
54 static int is_program_ignored(char const *filename, char const *ignore) {
56 size_t filename_length = strlen(filename);
59 debug(" is_program_ignored(\"%s\", \"%s\")\n", filename, ignore);
62 for (; *ignore; ignore += length) {
63 while (*ignore == ',') {
67 length = strcspn(ignore, ",");
72 if (length != filename_length) {
75 if (!strncmp(filename, ignore, length)) {
83 static int init_tracked_fds_list(size_t count) {
86 /* Reduce reallocs. */
87 count += TRACKFDS_REALLOC_STEP;
89 tracked_fds_list = malloc(count * sizeof(*tracked_fds_list));
90 if (!tracked_fds_list) {
92 warning("malloc(tracked_fds_list, %d) failed [%d]\n",
93 count * sizeof(*tracked_fds_list), getpid());
98 tracked_fds_list_space = count;
103 * Load tracked file descriptors from the environment. The environment is used
104 * to pass the information to child processes.
106 * ENV_NAME_FDS and ENV_NAME_PRIVATE_FDS have the following format: Each
107 * descriptor as string followed by a comma; there's a trailing comma.
110 static void init_from_environment(void) {
112 debug("init_from_environment()\t\t[%d]\n", getpid());
116 int saved_errno = errno;
118 assert(!initialized);
121 tracked_fds_list_count = 0;
123 /* Don't color writes to stderr for this binary (and its children) if it's
124 * contained in the comma-separated list in ENV_NAME_IGNORED_BINARIES. */
125 env = getenv(ENV_NAME_IGNORED_BINARIES);
129 /* TODO: Don't require /proc/. */
130 ssize_t written = readlink("/proc/self/exe", path, sizeof(path) - 1);
132 path[written] = 0; /* readlink() does not null-terminate! */
133 if (is_program_ignored(path, env)) {
139 /* If ENV_NAME_FORCE_WRITE is set and not empty, allow writes to a non-tty
140 * device. Use with care! Mainly used for the test suite. */
141 env = getenv(ENV_NAME_FORCE_WRITE);
142 if (env && env[0] != '\0') {
143 force_write_to_non_tty = 1;
146 /* Prefer user defined list of file descriptors, fall back to file
147 * descriptors passed through the environment from the parent process. */
148 env = getenv(ENV_NAME_FDS);
150 used_fds_set_by_user = 1;
152 env = getenv(ENV_NAME_PRIVATE_FDS);
159 debug(" getenv(\"%s\"): \"%s\"\n", ENV_NAME_FDS, env);
160 debug(" getenv(\"%s\"): \"%s\"\n", ENV_NAME_PRIVATE_FDS, env);
163 /* Environment must be treated read-only. */
164 char env_copy[strlen(env) + 1];
165 strcpy(env_copy, env);
170 for (x = env_copy; *x; x++) {
178 /* Parse file descriptor numbers from environment string and store them as
179 * integers in tracked_fds and tracked_fds_list. */
181 for (x = env_copy, last = env_copy; *x; x++) {
185 /* ',' at the beginning or double ',' - ignore. */
190 /* Replace ',' to null-terminate number for atoi(). */
197 } else if (fd < TRACKFDS_STATIC_COUNT) {
200 if (!tracked_fds_list) {
201 /* Pessimistic count estimate, but allocating a few more
202 * elements doesn't hurt. */
203 if (!init_tracked_fds_list(count)) {
204 /* Couldn't allocate memory, skip this entry. */
208 tracked_fds_list[i++] = fd;
210 debug(" large fd: %d\n", fd);
218 tracked_fds_list_count = i;
227 static char *update_environment_buffer_entry(char *x, int fd) {
230 int length = snprintf(x, 10 + 1, "%d", fd);
231 if (length >= 10 + 1 || length <= 0 /* shouldn't happen */) {
232 /* Integer too big to fit the buffer, skip it. */
234 warning("update_environment_buffer_entry(): truncated fd: %d [%d]\n",
240 /* Write comma after number. */
243 /* Make sure the string is always null-terminated. */
248 static void update_environment_buffer(char *x) {
252 for (i = 0; i < TRACKFDS_STATIC_COUNT; i++) {
253 if (tracked_fds[i]) {
254 x = update_environment_buffer_entry(x, (int)i);
257 for (i = 0; i < tracked_fds_list_count; i++) {
258 x = update_environment_buffer_entry(x, tracked_fds_list[i]);
261 inline static size_t update_environment_buffer_size(void) {
264 /* Use the maximum count (TRACKFDS_STATIC_COUNT) of used descriptors
265 * because it's simple and small enough not to be a problem.
267 * An integer (32-bit) has at most 10 digits, + 1 for the comma after each
268 * number. Bigger file descriptors (which shouldn't occur in reality) are
270 return (TRACKFDS_STATIC_COUNT + tracked_fds_list_count)
271 * (10 + 1) + 1 /* to fit '\0' */;
273 static void update_environment(void) {
275 debug("update_environment()\t\t[%d]\n", getpid());
278 /* If we haven't parsed the environment we also haven't modified it - so
284 int saved_errno = errno;
286 char env[update_environment_buffer_size()];
289 update_environment_buffer(env);
292 debug(" setenv(\"%s\", \"%s\", 1)\n", ENV_NAME_PRIVATE_FDS, env);
294 setenv(ENV_NAME_PRIVATE_FDS, env, 1 /* overwrite */);
296 /* Child processes must use ENV_NAME_PRIVATE_FDS to get the updated list
297 * of tracked file descriptors, not the static list provided by the user
300 * But only remove it if the static list in ENV_NAME_FDS was loaded by
301 * init_from_environment() and merged into ENV_NAME_PRIVATE_FDS. */
302 if (used_fds_set_by_user) {
303 unsetenv(ENV_NAME_FDS);
311 static void tracked_fds_add(int fd) {
314 if (fd < TRACKFDS_STATIC_COUNT) {
317 debug("tracked_fds_add(): %-3d\t\t[%d]\n", fd, getpid());
323 if (tracked_fds_list_count >= tracked_fds_list_space) {
324 int saved_errno = errno;
326 size_t new_space = tracked_fds_list_space + TRACKFDS_REALLOC_STEP;
327 int *tmp = realloc(tracked_fds_list,
328 sizeof(*tracked_fds_list) * new_space);
330 /* We can do nothing, just ignore the error. We made sure not to
331 * destroy our state, so the new descriptor is ignored without any
332 * other consequences. */
334 warning("realloc(tracked_fds_list, %zu) failed! [%d]\n",
335 sizeof(*tracked_fds_list) * new_space, getpid());
342 tracked_fds_list = tmp;
343 tracked_fds_list_space = new_space;
346 tracked_fds_list[tracked_fds_list_count++] = fd;
349 debug("tracked_fds_add(): %-3d\t\t[%d]\n", fd, getpid());
353 static int tracked_fds_remove(int fd) {
356 if (fd < TRACKFDS_STATIC_COUNT) {
357 int old_value = tracked_fds[fd];
361 debug("tracked_fds_remove(): %-3d\t[%d]\n", fd, getpid());
364 return old_value; /* Found vs. not found. */
368 for (i = 0; i < tracked_fds_list_count; i++) {
369 if (fd != tracked_fds_list[i]) {
373 memmove(tracked_fds_list + i, tracked_fds_list + i + 1,
374 sizeof(*tracked_fds_list) * (tracked_fds_list_count - i - 1));
375 tracked_fds_list_count--;
378 debug("tracked_fds_remove(): %-3d\t[%d]\n", fd, getpid());
390 static int tracked_fds_find_slow(int fd) noinline;
392 * tracked_fds_find() is called for each hook call and should be as fast as
393 * possible. As most file descriptors are < TRACKFDS_STATIC_COUNT, force the
394 * compiler to inline that part which is almost exclusively used.
396 * Inlining tracked_fds_add()/tracked_fds_remove() isn't worth the effort as
397 * they are not called often enough.
399 inline static int tracked_fds_find(int fd) always_inline;
400 inline static int tracked_fds_find(int fd) {
401 /* Invalid file descriptor. No assert() as we're called from the hooked
403 if (unlikely(fd < 0)) {
407 if (likely(fd < TRACKFDS_STATIC_COUNT)) {
408 return tracked_fds[fd];
411 return tracked_fds_find_slow(fd);
413 static int tracked_fds_find_slow(int fd) {
417 if (tracked_fds_list_count == 0) {
422 for (i = 0; i < tracked_fds_list_count; i++) {
423 if (fd == tracked_fds_list[i]) {