tjh.dev
1#define _GNU_SOURCE
2#include <stdio.h>
3#include <stdarg.h>
4#include <stdlib.h>
5#include <unistd.h>
6#include <dlfcn.h>
7#include <sys/types.h>
8#include <sys/stat.h>
9#include <fcntl.h>
10#include <limits.h>
11#include <string.h>
12#include <spawn.h>
13#include <dirent.h>
14
15#define MAX_REDIRECTS 128
16
17#ifdef __APPLE__
18 struct dyld_interpose {
19 const void * replacement;
20 const void * replacee;
21 };
22 #define WRAPPER(ret, name) static ret _libredirect_wrapper_##name
23 #define LOOKUP_REAL(name) &name
24 #define WRAPPER_DEF(name) \
25 __attribute__((used)) static struct dyld_interpose _libredirect_interpose_##name \
26 __attribute__((section("__DATA,__interpose"))) = { &_libredirect_wrapper_##name, &name };
27#else
28 #define WRAPPER(ret, name) ret name
29 #define LOOKUP_REAL(name) dlsym(RTLD_NEXT, #name)
30 #define WRAPPER_DEF(name)
31#endif
32
33static int nrRedirects = 0;
34static char * from[MAX_REDIRECTS];
35static char * to[MAX_REDIRECTS];
36
37static int isInitialized = 0;
38
39// FIXME: might run too late.
40static void init() __attribute__((constructor));
41
42static void init()
43{
44 if (isInitialized) return;
45
46 char * spec = getenv("NIX_REDIRECTS");
47 if (!spec) return;
48
49 // Ensure we only run this code once.
50 // We do not do `unsetenv("NIX_REDIRECTS")` to ensure that redirects
51 // also get initialized for subprocesses.
52 isInitialized = 1;
53
54 char * spec2 = malloc(strlen(spec) + 1);
55 strcpy(spec2, spec);
56
57 char * pos = spec2, * eq;
58 while ((eq = strchr(pos, '='))) {
59 *eq = 0;
60 from[nrRedirects] = pos;
61 pos = eq + 1;
62 to[nrRedirects] = pos;
63 nrRedirects++;
64 if (nrRedirects == MAX_REDIRECTS) break;
65 char * end = strchr(pos, ':');
66 if (!end) break;
67 *end = 0;
68 pos = end + 1;
69 }
70
71}
72
73static const char * rewrite(const char * volatile path, char * buf)
74{
75 // Marking the path volatile is needed so the the following check isn't
76 // optimized away by the compiler.
77 if (path == NULL) return path;
78
79 for (int n = 0; n < nrRedirects; ++n) {
80 int len = strlen(from[n]);
81 if (strncmp(path, from[n], len) != 0) continue;
82 if (snprintf(buf, PATH_MAX, "%s%s", to[n], path + len) >= PATH_MAX)
83 abort();
84 return buf;
85 }
86
87 return path;
88}
89
90static char * rewrite_non_const(char * path, char * buf)
91{
92 // as long as the argument `path` is non-const, we can consider discarding
93 // the const qualifier of the return value to be safe.
94 return (char *)rewrite(path, buf);
95}
96
97static int open_needs_mode(int flags)
98{
99#ifdef O_TMPFILE
100 return (flags & O_CREAT) || (flags & O_TMPFILE) == O_TMPFILE;
101#else
102 return flags & O_CREAT;
103#endif
104}
105
106/* The following set of Glibc library functions is very incomplete -
107 it contains only what we needed for programs in Nixpkgs. Just add
108 more functions as needed. */
109
110WRAPPER(int, open)(const char * path, int flags, ...)
111{
112 int (*open_real) (const char *, int, ...) = LOOKUP_REAL(open);
113 mode_t mode = 0;
114 if (open_needs_mode(flags)) {
115 va_list ap;
116 va_start(ap, flags);
117 mode = va_arg(ap, mode_t);
118 va_end(ap);
119 }
120 char buf[PATH_MAX];
121 return open_real(rewrite(path, buf), flags, mode);
122}
123WRAPPER_DEF(open)
124
125// In musl libc, open64 is simply a macro for open
126#if !defined(__APPLE__) && !defined(open64)
127WRAPPER(int, open64)(const char * path, int flags, ...)
128{
129 int (*open64_real) (const char *, int, mode_t) = LOOKUP_REAL(open64);
130 mode_t mode = 0;
131 if (open_needs_mode(flags)) {
132 va_list ap;
133 va_start(ap, flags);
134 mode = va_arg(ap, mode_t);
135 va_end(ap);
136 }
137 char buf[PATH_MAX];
138 return open64_real(rewrite(path, buf), flags, mode);
139}
140WRAPPER_DEF(open64)
141#endif
142
143WRAPPER(int, openat)(int dirfd, const char * path, int flags, ...)
144{
145 int (*openat_real) (int, const char *, int, ...) = LOOKUP_REAL(openat);
146 mode_t mode = 0;
147 if (open_needs_mode(flags)) {
148 va_list ap;
149 va_start(ap, flags);
150 mode = va_arg(ap, mode_t);
151 va_end(ap);
152 }
153 char buf[PATH_MAX];
154 return openat_real(dirfd, rewrite(path, buf), flags, mode);
155}
156WRAPPER_DEF(openat)
157
158WRAPPER(FILE *, fopen)(const char * path, const char * mode)
159{
160 FILE * (*fopen_real) (const char *, const char *) = LOOKUP_REAL(fopen);
161 char buf[PATH_MAX];
162 return fopen_real(rewrite(path, buf), mode);
163}
164WRAPPER_DEF(fopen)
165
166#ifdef __GLIBC__
167WRAPPER(FILE *, __nss_files_fopen)(const char * path)
168{
169 FILE * (*__nss_files_fopen_real) (const char *) = LOOKUP_REAL(__nss_files_fopen);
170 char buf[PATH_MAX];
171 return __nss_files_fopen_real(rewrite(path, buf));
172}
173WRAPPER_DEF(__nss_files_fopen)
174#endif
175
176// In musl libc, fopen64 is simply a macro for fopen
177#if !defined(__APPLE__) && !defined(fopen64)
178WRAPPER(FILE *, fopen64)(const char * path, const char * mode)
179{
180 FILE * (*fopen64_real) (const char *, const char *) = LOOKUP_REAL(fopen64);
181 char buf[PATH_MAX];
182 return fopen64_real(rewrite(path, buf), mode);
183}
184WRAPPER_DEF(fopen64)
185#endif
186
187#ifdef __linux__
188WRAPPER(int, __xstat)(int ver, const char * path, struct stat * st)
189{
190 int (*__xstat_real) (int ver, const char *, struct stat *) = LOOKUP_REAL(__xstat);
191 char buf[PATH_MAX];
192 return __xstat_real(ver, rewrite(path, buf), st);
193}
194WRAPPER_DEF(__xstat)
195#endif
196
197#ifdef __linux__
198WRAPPER(int, __xstat64)(int ver, const char * path, struct stat64 * st)
199{
200 int (*__xstat64_real) (int ver, const char *, struct stat64 *) = LOOKUP_REAL(__xstat64);
201 char buf[PATH_MAX];
202 return __xstat64_real(ver, rewrite(path, buf), st);
203}
204WRAPPER_DEF(__xstat64)
205#endif
206
207#if defined(__linux__) && defined(STATX_TYPE)
208WRAPPER(int, statx)(int dirfd, const char * restrict pathname, int flags,
209 unsigned int mask, struct statx * restrict statxbuf)
210{
211 int (*statx_real) (int, const char * restrict, int,
212 unsigned int, struct statx * restrict) = LOOKUP_REAL(statx);
213 char buf[PATH_MAX];
214 return statx_real(dirfd, rewrite(pathname, buf), flags, mask, statxbuf);
215}
216WRAPPER_DEF(statx)
217#endif
218
219WRAPPER(int, fstatat)(int dirfd, const char * pathname, struct stat * statbuf, int flags)
220{
221 int (*fstatat_real) (int, const char *, struct stat *, int) = LOOKUP_REAL(fstatat);
222 char buf[PATH_MAX];
223 return fstatat_real(dirfd, rewrite(pathname, buf), statbuf, flags);
224}
225WRAPPER_DEF(fstatat);
226
227// In musl libc, fstatat64 is simply a macro for fstatat
228#if !defined(__APPLE__) && !defined(fstatat64)
229WRAPPER(int, fstatat64)(int dirfd, const char * pathname, struct stat64 * statbuf, int flags)
230{
231 int (*fstatat64_real) (int, const char *, struct stat64 *, int) = LOOKUP_REAL(fstatat64);
232 char buf[PATH_MAX];
233 return fstatat64_real(dirfd, rewrite(pathname, buf), statbuf, flags);
234}
235WRAPPER_DEF(fstatat64);
236#endif
237
238WRAPPER(int, stat)(const char * path, struct stat * st)
239{
240 int (*__stat_real) (const char *, struct stat *) = LOOKUP_REAL(stat);
241 char buf[PATH_MAX];
242 return __stat_real(rewrite(path, buf), st);
243}
244WRAPPER_DEF(stat)
245
246// In musl libc, stat64 is simply a macro for stat
247#if !defined(__APPLE__) && !defined(stat64)
248WRAPPER(int, stat64)(const char * path, struct stat64 * st)
249{
250 int (*stat64_real) (const char *, struct stat64 *) = LOOKUP_REAL(stat64);
251 char buf[PATH_MAX];
252 return stat64_real(rewrite(path, buf), st);
253}
254WRAPPER_DEF(stat64)
255#endif
256
257WRAPPER(int, access)(const char * path, int mode)
258{
259 int (*access_real) (const char *, int mode) = LOOKUP_REAL(access);
260 char buf[PATH_MAX];
261 return access_real(rewrite(path, buf), mode);
262}
263WRAPPER_DEF(access)
264
265WRAPPER(int, posix_spawn)(pid_t * pid, const char * path,
266 const posix_spawn_file_actions_t * file_actions,
267 const posix_spawnattr_t * attrp,
268 char * const argv[], char * const envp[])
269{
270 int (*posix_spawn_real) (pid_t *, const char *,
271 const posix_spawn_file_actions_t *,
272 const posix_spawnattr_t *,
273 char * const argv[], char * const envp[]) = LOOKUP_REAL(posix_spawn);
274 char buf[PATH_MAX];
275 return posix_spawn_real(pid, rewrite(path, buf), file_actions, attrp, argv, envp);
276}
277WRAPPER_DEF(posix_spawn)
278
279WRAPPER(int, posix_spawnp)(pid_t * pid, const char * file,
280 const posix_spawn_file_actions_t * file_actions,
281 const posix_spawnattr_t * attrp,
282 char * const argv[], char * const envp[])
283{
284 int (*posix_spawnp_real) (pid_t *, const char *,
285 const posix_spawn_file_actions_t *,
286 const posix_spawnattr_t *,
287 char * const argv[], char * const envp[]) = LOOKUP_REAL(posix_spawnp);
288 char buf[PATH_MAX];
289 return posix_spawnp_real(pid, rewrite(file, buf), file_actions, attrp, argv, envp);
290}
291WRAPPER_DEF(posix_spawnp)
292
293WRAPPER(int, execv)(const char * path, char * const argv[])
294{
295 int (*execv_real) (const char * path, char * const argv[]) = LOOKUP_REAL(execv);
296 char buf[PATH_MAX];
297 return execv_real(rewrite(path, buf), argv);
298}
299WRAPPER_DEF(execv)
300
301WRAPPER(int, execvp)(const char * path, char * const argv[])
302{
303 int (*_execvp) (const char *, char * const argv[]) = LOOKUP_REAL(execvp);
304 char buf[PATH_MAX];
305 return _execvp(rewrite(path, buf), argv);
306}
307WRAPPER_DEF(execvp)
308
309WRAPPER(int, execve)(const char * path, char * const argv[], char * const envp[])
310{
311 int (*_execve) (const char *, char * const argv[], char * const envp[]) = LOOKUP_REAL(execve);
312 char buf[PATH_MAX];
313 return _execve(rewrite(path, buf), argv, envp);
314}
315WRAPPER_DEF(execve)
316
317WRAPPER(DIR *, opendir)(const char * path)
318{
319 char buf[PATH_MAX];
320 DIR * (*_opendir) (const char*) = LOOKUP_REAL(opendir);
321
322 return _opendir(rewrite(path, buf));
323}
324WRAPPER_DEF(opendir)
325
326#define SYSTEM_CMD_MAX 512
327
328static char * replace_substring(char * source, char * buf, char * replace_string, char * start_ptr, char * suffix_ptr) {
329 char head[SYSTEM_CMD_MAX] = {0};
330 strncpy(head, source, start_ptr - source);
331
332 char tail[SYSTEM_CMD_MAX] = {0};
333 if(suffix_ptr < source + strlen(source)) {
334 strcpy(tail, suffix_ptr);
335 }
336
337 sprintf(buf, "%s%s%s", head, replace_string, tail);
338 return buf;
339}
340
341static char * replace_string(char * buf, char * from, char * to) {
342 int num_matches = 0;
343 char * matches[SYSTEM_CMD_MAX];
344 int from_len = strlen(from);
345 for(int i=0; i<strlen(buf); i++){
346 char *cmp_start = buf + i;
347 if(strncmp(from, cmp_start, from_len) == 0){
348 matches[num_matches] = cmp_start;
349 num_matches++;
350 }
351 }
352 int len_diff = strlen(to) - strlen(from);
353 for(int n = 0; n < num_matches; n++) {
354 char replaced[SYSTEM_CMD_MAX];
355 replace_substring(buf, replaced, to, matches[n], matches[n]+from_len);
356 strcpy(buf, replaced);
357 for(int nn = n+1; nn < num_matches; nn++) {
358 matches[nn] += len_diff;
359 }
360 }
361 return buf;
362}
363
364static void rewriteSystemCall(const char * command, char * buf) {
365 char * p = buf;
366
367 #ifdef __APPLE__
368 // The dyld environment variable is not inherited by the subprocess spawned
369 // by system(), so this hack redefines it.
370 Dl_info info;
371 dladdr(&rewriteSystemCall, &info);
372 p = stpcpy(p, "export DYLD_INSERT_LIBRARIES=");
373 p = stpcpy(p, info.dli_fname);
374 p = stpcpy(p, ";");
375 #endif
376
377 stpcpy(p, command);
378
379 for (int n = 0; n < nrRedirects; ++n) {
380 replace_string(buf, from[n], to[n]);
381 }
382}
383
384WRAPPER(int, system)(const char *command)
385{
386 int (*_system) (const char*) = LOOKUP_REAL(system);
387
388 char newCommand[SYSTEM_CMD_MAX];
389 rewriteSystemCall(command, newCommand);
390 return _system(newCommand);
391}
392WRAPPER_DEF(system)
393
394WRAPPER(int, chdir)(const char *path)
395{
396 int (*chdir_real) (const char *) = LOOKUP_REAL(chdir);
397 char buf[PATH_MAX];
398 return chdir_real(rewrite(path, buf));
399}
400WRAPPER_DEF(chdir);
401
402WRAPPER(int, mkdir)(const char *path, mode_t mode)
403{
404 int (*mkdir_real) (const char *path, mode_t mode) = LOOKUP_REAL(mkdir);
405 char buf[PATH_MAX];
406 return mkdir_real(rewrite(path, buf), mode);
407}
408WRAPPER_DEF(mkdir)
409
410WRAPPER(int, mkdirat)(int dirfd, const char *path, mode_t mode)
411{
412 int (*mkdirat_real) (int dirfd, const char *path, mode_t mode) = LOOKUP_REAL(mkdirat);
413 char buf[PATH_MAX];
414 return mkdirat_real(dirfd, rewrite(path, buf), mode);
415}
416WRAPPER_DEF(mkdirat)
417
418WRAPPER(int, unlink)(const char *path)
419{
420 int (*unlink_real) (const char *path) = LOOKUP_REAL(unlink);
421 char buf[PATH_MAX];
422 return unlink_real(rewrite(path, buf));
423}
424WRAPPER_DEF(unlink)
425
426WRAPPER(int, unlinkat)(int dirfd, const char *path, int flags)
427{
428 int (*unlinkat_real) (int dirfd, const char *path, int flags) = LOOKUP_REAL(unlinkat);
429 char buf[PATH_MAX];
430 return unlinkat_real(dirfd, rewrite(path, buf), flags);
431}
432WRAPPER_DEF(unlinkat)
433
434WRAPPER(int, rmdir)(const char *path)
435{
436 int (*rmdir_real) (const char *path) = LOOKUP_REAL(rmdir);
437 char buf[PATH_MAX];
438 return rmdir_real(rewrite(path, buf));
439}
440WRAPPER_DEF(rmdir)
441
442static void copy_temp_wildcard(char * dest, char * src, int suffixlen) {
443 int dest_len = strnlen(dest, PATH_MAX);
444 int src_len = strnlen(src, PATH_MAX);
445 memcpy(dest + dest_len - (6 + suffixlen), src + src_len - (6 + suffixlen), 6);
446}
447
448WRAPPER(int, mkstemp)(char *template)
449{
450 int (*mkstemp_real) (char *template) = LOOKUP_REAL(mkstemp);
451 char buf[PATH_MAX];
452 char * rewritten = rewrite_non_const(template, buf);
453 int retval = mkstemp_real(rewritten);
454 if (retval >= 0 && rewritten != template) {
455 copy_temp_wildcard(template, rewritten, 0);
456 }
457 return retval;
458}
459WRAPPER_DEF(mkstemp)
460
461WRAPPER(int, mkostemp)(char *template, int flags)
462{
463 int (*mkostemp_real) (char *template, int flags) = LOOKUP_REAL(mkostemp);
464 char buf[PATH_MAX];
465 char * rewritten = rewrite_non_const(template, buf);
466 int retval = mkostemp_real(rewritten, flags);
467 if (retval >= 0 && rewritten != template) {
468 copy_temp_wildcard(template, rewritten, 0);
469 }
470 return retval;
471}
472WRAPPER_DEF(mkostemp)
473
474WRAPPER(int, mkstemps)(char *template, int suffixlen)
475{
476 int (*mkstemps_real) (char *template, int suffixlen) = LOOKUP_REAL(mkstemps);
477 char buf[PATH_MAX];
478 char * rewritten = rewrite_non_const(template, buf);
479 int retval = mkstemps_real(rewritten, suffixlen);
480 if (retval >= 0 && rewritten != template) {
481 copy_temp_wildcard(template, rewritten, suffixlen);
482 }
483 return retval;
484}
485WRAPPER_DEF(mkstemps)
486
487WRAPPER(int, mkostemps)(char *template, int suffixlen, int flags)
488{
489 int (*mkostemps_real) (char *template, int suffixlen, int flags) = LOOKUP_REAL(mkostemps);
490 char buf[PATH_MAX];
491 char * rewritten = rewrite_non_const(template, buf);
492 int retval = mkostemps_real(rewritten, suffixlen, flags);
493 if (retval >= 0 && rewritten != template) {
494 copy_temp_wildcard(template, rewritten, suffixlen);
495 }
496 return retval;
497}
498WRAPPER_DEF(mkostemps)
499
500WRAPPER(char *, mkdtemp)(char *template)
501{
502 char * (*mkdtemp_real) (char *template) = LOOKUP_REAL(mkdtemp);
503 char buf[PATH_MAX];
504 char * rewritten = rewrite_non_const(template, buf);
505 char * retval = mkdtemp_real(rewritten);
506 if (retval == NULL) {
507 return retval;
508 };
509 if (rewritten != template) {
510 copy_temp_wildcard(template, rewritten, 0);
511 }
512 return template;
513}
514WRAPPER_DEF(mkdtemp)
515
516WRAPPER(char *, mktemp)(char *template)
517{
518 char * (*mktemp_real) (char *template) = LOOKUP_REAL(mktemp);
519 char buf[PATH_MAX];
520 char * rewritten = rewrite_non_const(template, buf);
521 char * retval = mktemp_real(rewritten);
522 if (retval == NULL) {
523 return retval;
524 };
525 if (rewritten != template) {
526 copy_temp_wildcard(template, rewritten, 0);
527 }
528 return template;
529}
530WRAPPER_DEF(mktemp)