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