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
  20 #define LTTNG_UST_DLSYM_FAILED_PTR 0x1
  21
  22 static int (*__lttng_ust_fd_plibc_close)(int fd) = NULL;
  23 static int (*__lttng_ust_fd_plibc_fclose)(FILE *stream) = NULL;
  24 static int (*__lttng_ust_fd_plibc_close_range)(unsigned int first,
  25                 unsigned int last, int flags) = NULL;
  26
  27 /*
  28  * Use dlsym to find the original libc close() symbol and store it in
  29  * __lttng_ust_fd_plibc_close.
  30  */
  31 static
  32 void *_lttng_ust_fd_init_plibc_close(void)
  33 {
  34         if (__lttng_ust_fd_plibc_close == NULL) {
  35                 __lttng_ust_fd_plibc_close = dlsym(RTLD_NEXT, "close");
  36
  37                 if (__lttng_ust_fd_plibc_close == NULL) {
  38                         __lttng_ust_fd_plibc_close = (void *) LTTNG_UST_DLSYM_FAILED_PTR;
  39                         fprintf(stderr, "%s\n", dlerror());
  40                 }
  41         }
  42
  43         return __lttng_ust_fd_plibc_close;
  44 }
  45
  46 /*
  47  * Use dlsym to find the original libc fclose() symbol and store it in
  48  * __lttng_ust_fd_plibc_fclose.
  49  */
  50 static
  51 void *_lttng_ust_fd_init_plibc_fclose(void)
  52 {
  53         if (__lttng_ust_fd_plibc_fclose == NULL) {
  54                 __lttng_ust_fd_plibc_fclose = dlsym(RTLD_NEXT, "fclose");
  55
  56                 if (__lttng_ust_fd_plibc_fclose == NULL) {
  57                         __lttng_ust_fd_plibc_fclose = (void *) LTTNG_UST_DLSYM_FAILED_PTR;
  58                         fprintf(stderr, "%s\n", dlerror());
  59                 }
  60         }
  61
  62         return __lttng_ust_fd_plibc_fclose;
  63 }
  64
  65 /*
  66  * Use dlsym to find the original libc close_range() symbol and store it
  67  * in __lttng_ust_fd_plibc_close_range. The close_range symbol only
  68  * appears in glibc 2.34, so it is considered optional.
  69  */
  70 static
  71 void *_lttng_ust_fd_init_plibc_close_range(void)
  72 {
  73         if (__lttng_ust_fd_plibc_close_range == NULL) {
  74                 __lttng_ust_fd_plibc_close_range = dlsym(RTLD_NEXT, "close_range");
  75
  76                 if (__lttng_ust_fd_plibc_close_range == NULL)
  77                         __lttng_ust_fd_plibc_close_range = (void *) LTTNG_UST_DLSYM_FAILED_PTR;
  78         }
  79
  80         return __lttng_ust_fd_plibc_close_range;
  81 }
  82
  83 static
  84 void _lttng_ust_fd_ctor(void)
  85         __attribute__((constructor));
  86 static
  87 void _lttng_ust_fd_ctor(void)
  88 {
  89         lttng_ust_common_ctor();
  90
  91         /*
  92          * Initialize the function pointers to the original libc symbols in the
  93          * constructor since close() has to stay async-signal-safe and as such,
  94          * we can't call dlsym() in the override functions.
  95          */
  96         (void) _lttng_ust_fd_init_plibc_close();
  97         (void) _lttng_ust_fd_init_plibc_fclose();
  98         (void) _lttng_ust_fd_init_plibc_close_range();
  99 }
 100
 101 /*
 102  * Override the libc close() symbol with our own, allowing applications to
 103  * close arbitrary file descriptors. If the fd is owned by lttng-ust, return
 104  * -1, errno=EBADF instead of closing it.
 105  *
 106  * If dlsym failed to find the original libc close() symbol, return -1,
 107  * errno=ENOSYS.
 108  *
 109  * There is a short window before the library constructor has executed where
 110  * this wrapper could call dlsym() and thus not be async-signal-safe.
 111  */
 112 int close(int fd)
 113 {
 114         /*
 115          * We can't retry dlsym here since close is async-signal-safe.
 116          */
 117         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 118                 errno = ENOSYS;
 119                 return -1;
 120         }
 121
 122         return lttng_ust_safe_close_fd(fd, __lttng_ust_fd_plibc_close);
 123 }
 124
 125 /*
 126  * Override the libc fclose() symbol with our own, allowing applications to
 127  * close arbitrary streams. If the fd is owned by lttng-ust, return -1,
 128  * errno=EBADF instead of closing it.
 129  *
 130  * If dlsym failed to find the original libc close() symbol, return -1,
 131  * errno=ENOSYS.
 132  *
 133  * There is a short window before the library constructor has executed where
 134  * this wrapper could call dlsym() and thus not be async-signal-safe.
 135  *
 136  * Note: fcloseall() is not an issue because it closes only the streams it
 137  * knows about, which differs from the problems caused by gnulib
 138  * close_stdout(), which does an explicit fclose(stdout).
 139  */
 140 int fclose(FILE *stream)
 141 {
 142         if (_lttng_ust_fd_init_plibc_fclose() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 143                 errno = ENOSYS;
 144                 return -1;
 145         }
 146
 147         return lttng_ust_safe_fclose_stream(stream,
 148                         __lttng_ust_fd_plibc_fclose);
 149 }
 150
 151 /*
 152  * Override the libc close_range() symbol with our own, allowing
 153  * applications to close arbitrary file descriptors. If the fd is owned
 154  * by lttng-ust, return -1, errno=EBADF instead of closing it.
 155  *
 156  * If dlsym failed to find the original libc close_range() symbol,
 157  * return -1, errno=ENOSYS.
 158  *
 159  * There is a short window before the library constructor has executed where
 160  * this wrapper could call dlsym() and thus not be async-signal-safe.
 161  */
 162 int close_range(unsigned int first, unsigned int last, int flags)
 163 {
 164         /*
 165          * We can't retry dlsym here since close is async-signal-safe.
 166          */
 167         if (_lttng_ust_fd_init_plibc_close_range() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 168                 errno = ENOSYS;
 169                 return -1;
 170         }
 171
 172         return lttng_ust_safe_close_range_fd(first, last, flags, __lttng_ust_fd_plibc_close_range);
 173 }
 174
 175 #if defined(__sun__) || defined(__FreeBSD__)
 176 /* Solaris and FreeBSD. */
 177 void closefrom(int lowfd)
 178 {
 179         if (_lttng_ust_fd_init_plibc_close() == (void *) LTTNG_UST_DLSYM_FAILED_PTR) {
 180                 return;
 181         }
 182
 183         (void) lttng_ust_safe_closefrom_fd(lowfd, __lttng_ust_fd_plibc_close);
 184 }
 185 #elif defined(__NetBSD__) || defined(__OpenBSD__)
 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