src/lib/lttng-ust-fd/lttng-ust-fd.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2016  Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  */
   6
   7 #define _LGPL_SOURCE
   8 #include <limits.h>
   9 #include <stdio.h>
  10 #include <sys/types.h>
  11 #include <unistd.h>
  12 #include <dlfcn.h>
  13 #include <errno.h>
  14
  15 #include <lttng/ust-common.h>
  16
  17 #include "common/macros.h"
  18 #include "common/ust-fd.h"
  19 #include "lib/lttng-ust-common/fd-tracker.h"
  20
  21 #define LTTNG_UST_DLSYM_FAILED_PTR 0x1
  22
  23 static int (*__lttng_ust_fd_plibc_close)(int fd) = NULL;
  24 static int (*__lttng_ust_fd_plibc_fclose)(FILE *stream) = NULL;
  25
  26 /*
  27  * Use dlsym to find the original libc close() symbol and store it in
  28  * __lttng_ust_fd_plibc_close.
  29  */
  30 static
  31 void *_lttng_ust_fd_init_plibc_close(void)
  32 {
  33         if (__lttng_ust_fd_plibc_close == NULL) {
  34                 __lttng_ust_fd_plibc_close = dlsym(RTLD_NEXT, "close");
  35
  36                 if (__lttng_ust_fd_plibc_close == NULL) {
  37                         __lttng_ust_fd_plibc_close = (void *) LTTNG_UST_DLSYM_FAILED_PTR;
  38                         fprintf(stderr, "%s\n", dlerror());
  39                 }
  40         }
  41
  42         return __lttng_ust_fd_plibc_close;
  43 }
  44
  45 /*
  46  * Use dlsym to find the original libc fclose() symbol and store it in
  47  * __lttng_ust_fd_plibc_fclose.
  48  */
  49 static
  50 void *_lttng_ust_fd_init_plibc_fclose(void)
  51 {
  52         if (__lttng_ust_fd_plibc_fclose == NULL) {
  53                 __lttng_ust_fd_plibc_fclose = dlsym(RTLD_NEXT, "fclose");
  54
  55                 if (__lttng_ust_fd_plibc_fclose == NULL) {
  56                         __lttng_ust_fd_plibc_fclose = (void *) LTTNG_UST_DLSYM_FAILED_PTR;
  57                         fprintf(stderr, "%s\n", dlerror());
  58                 }
  59         }
  60
  61         return __lttng_ust_fd_plibc_fclose;
  62 }
  63
  64 #if !defined(LTTNG_UST_CUSTOM_UPGRADE_CONFLICTING_SYMBOLS)
  65
  66 static void *lttng_ust_2_12_handle;
  67
  68 static
  69 void lttng_ust_init_close_chaining(void)
  70 {
  71         if (lttng_ust_2_12_handle)
  72                 return;
  73         /*
  74          * Load ust-2.12 in the global symbol namespace.
  75          */
  76         lttng_ust_2_12_handle = dlopen("liblttng-ust.so.0", RTLD_GLOBAL | RTLD_NOW);
  77         if (!lttng_ust_2_12_handle) {
  78                 fprintf(stderr, "liblttng-ust-fd.so.1: Failed to dlopen liblttng-ust.so.0: %s\n", dlerror());
  79                 abort();
  80         }
  81         /*
  82          * Initialize the function pointers to the ust 2.12 symbols in
  83          * the constructor since close() has to stay async-signal-safe
  84          * and as such, we can't call dlsym() in the override functions.
  85          */
  86         (void) lttng_ust_safe_close_fd_init();
  87         (void) lttng_ust_safe_fclose_stream_init();
  88 }
  89 #else
  90 static
  91 void lttng_ust_init_close_chaining(void) { }
  92 #endif
  93
  94 static
  95 void _lttng_ust_fd_ctor(void)
  96         __attribute__((constructor));
  97 static
  98 void _lttng_ust_fd_ctor(void)
  99 {
 100         lttng_ust_init_close_chaining();
 101
 102         lttng_ust_common_ctor();
 103
 104         /*
 105          * Initialize the function pointers to the original libc symbols in the
 106          * constructor since close() has to stay async-signal-safe and as such,
 107          * we can't call dlsym() in the override functions.
 108          */
 109         (void) _lttng_ust_fd_init_plibc_close();
 110         (void) _lttng_ust_fd_init_plibc_fclose();
 111 }
 112
 113 /*
 114  * Override the libc close() symbol with our own, allowing applications to
 115  * close arbitrary file descriptors. If the fd is owned by lttng-ust, return
 116  * -1, errno=EBADF instead of closing it.
 117  *
 118  * If dlsym failed to find the original libc close() symbol, return -1,
 119  * errno=ENOSYS.
 120  *
 121  * There is a short window before the library constructor has executed where
 122  * this wrapper could call dlsym() and dlopen() and thus not be
 123  * async-signal-safe.
 124  */
 125 int close(int fd)
 126 {
 127         lttng_ust_init_close_chaining();
 128
 129         /*
 130          * We can't retry dlsym here since close is async-signal-safe.
 131          */
 132         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 133                 errno = ENOSYS;
 134                 return -1;
 135         }
 136
 137         return lttng_ust_safe_close_fd(fd, __lttng_ust_fd_plibc_close);
 138 }
 139
 140 /*
 141  * Override the libc fclose() symbol with our own, allowing applications to
 142  * close arbitrary streams. If the fd is owned by lttng-ust, return -1,
 143  * errno=EBADF instead of closing it.
 144  *
 145  * If dlsym failed to find the original libc close() symbol, return -1,
 146  * errno=ENOSYS.
 147  *
 148  * There is a short window before the library constructor has executed where
 149  * this wrapper could call dlsym() and thus not be async-signal-safe.
 150  *
 151  * Note: fcloseall() is not an issue because it closes only the streams it
 152  * knows about, which differs from the problems caused by gnulib
 153  * close_stdout(), which does an explicit fclose(stdout).
 154  */
 155 int fclose(FILE *stream)
 156 {
 157         lttng_ust_init_close_chaining();
 158
 159         if (_lttng_ust_fd_init_plibc_fclose() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 160                 errno = ENOSYS;
 161                 return -1;
 162         }
 163
 164         return lttng_ust_safe_fclose_stream(stream,
 165                         __lttng_ust_fd_plibc_fclose);
 166 }
 167
 168 #if defined(__sun__) || defined(__FreeBSD__)
 169
 170 #error "Custom upgrade branch does not support Solaris/FreeBSD closefrom"
 171
 172 /* Solaris and FreeBSD. */
 173 void closefrom(int lowfd)
 174 {
 175         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 176                 return;
 177         }
 178
 179         (void) lttng_ust_safe_closefrom_fd(lowfd, __lttng_ust_fd_plibc_close);
 180 }
 181 #elif defined(__NetBSD__) || defined(__OpenBSD__)
 182
 183 #error "Custom upgrade branch does not support NetBSD/OpenBSD closefrom"
 184
 185 /* NetBSD and OpenBSD. */
 186 int closefrom(int lowfd)
 187 {
 188         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 189                 errno = ENOSYS;
 190                 return -1;
 191         }
 192
 193         return lttng_ust_safe_closefrom_fd(lowfd, __lttng_ust_fd_plibc_close);
 194 }
 195 #else
 196 /* As far as we know, this OS does not implement closefrom. */
 197 #endif