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         (void) lttng_ust_get_fd_mutex_nest_init();
  89 }
  90 #else
  91 static
  92 void lttng_ust_init_close_chaining(void) { }
  93 #endif
  94
  95 static
  96 void _lttng_ust_fd_ctor(void)
  97         __attribute__((constructor));
  98 static
  99 void _lttng_ust_fd_ctor(void)
 100 {
 101         lttng_ust_init_close_chaining();
 102
 103         lttng_ust_common_ctor();
 104
 105         /*
 106          * Initialize the function pointers to the original libc symbols in the
 107          * constructor since close() has to stay async-signal-safe and as such,
 108          * we can't call dlsym() in the override functions.
 109          */
 110         (void) _lttng_ust_fd_init_plibc_close();
 111         (void) _lttng_ust_fd_init_plibc_fclose();
 112 }
 113
 114 /*
 115  * Override the libc close() symbol with our own, allowing applications to
 116  * close arbitrary file descriptors. If the fd is owned by lttng-ust, return
 117  * -1, errno=EBADF instead of closing it.
 118  *
 119  * If dlsym failed to find the original libc close() symbol, return -1,
 120  * errno=ENOSYS.
 121  *
 122  * There is a short window before the library constructor has executed where
 123  * this wrapper could call dlsym() and dlopen() and thus not be
 124  * async-signal-safe.
 125  */
 126 int close(int fd)
 127 {
 128         lttng_ust_init_close_chaining();
 129
 130         /*
 131          * We can't retry dlsym here since close is async-signal-safe.
 132          */
 133         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 134                 errno = ENOSYS;
 135                 return -1;
 136         }
 137
 138         return lttng_ust_safe_close_fd(fd, __lttng_ust_fd_plibc_close);
 139 }
 140
 141 /*
 142  * Override the libc fclose() symbol with our own, allowing applications to
 143  * close arbitrary streams. If the fd is owned by lttng-ust, return -1,
 144  * errno=EBADF instead of closing it.
 145  *
 146  * If dlsym failed to find the original libc close() symbol, return -1,
 147  * errno=ENOSYS.
 148  *
 149  * There is a short window before the library constructor has executed where
 150  * this wrapper could call dlsym() and thus not be async-signal-safe.
 151  *
 152  * Note: fcloseall() is not an issue because it closes only the streams it
 153  * knows about, which differs from the problems caused by gnulib
 154  * close_stdout(), which does an explicit fclose(stdout).
 155  */
 156 int fclose(FILE *stream)
 157 {
 158         lttng_ust_init_close_chaining();
 159
 160         if (_lttng_ust_fd_init_plibc_fclose() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 161                 errno = ENOSYS;
 162                 return -1;
 163         }
 164
 165         return lttng_ust_safe_fclose_stream(stream,
 166                         __lttng_ust_fd_plibc_fclose);
 167 }
 168
 169 #if defined(__sun__) || defined(__FreeBSD__)
 170
 171 #error "Custom upgrade branch does not support Solaris/FreeBSD closefrom"
 172
 173 /* Solaris and FreeBSD. */
 174 void closefrom(int lowfd)
 175 {
 176         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 177                 return;
 178         }
 179
 180         (void) lttng_ust_safe_closefrom_fd(lowfd, __lttng_ust_fd_plibc_close);
 181 }
 182 #elif defined(__NetBSD__) || defined(__OpenBSD__)
 183
 184 #error "Custom upgrade branch does not support NetBSD/OpenBSD closefrom"
 185
 186 /* NetBSD and OpenBSD. */
 187 int closefrom(int lowfd)
 188 {
 189         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 190                 errno = ENOSYS;
 191                 return -1;
 192         }
 193
 194         return lttng_ust_safe_closefrom_fd(lowfd, __lttng_ust_fd_plibc_close);
 195 }
 196 #else
 197 /* As far as we know, this OS does not implement closefrom. */
 198 #endif