mdw@git.distorted.org.uk Git - preload-hacks/blob - uopen.c

   1 /* -*-c-*-
   2  *
   3  * Allow open(2) to work on Unix-domain sockets
   4  *
   5  * (c) 2008 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the preload-hacks package.
  11  *
  12  * Preload-hacks are free software; you can redistribute it and/or modify
  13  * them under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or (at
  15  * your option) any later version.
  16  *
  17  * Preload-hacks are distributed in the hope that it will be useful, but
  18  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  19  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  20  * for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License along
  23  * with preload-hacks; if not, write to the Free Software Foundation, Inc.,
  24  * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 #define _GNU_SOURCE
  28 #undef sun
  29
  30 /*----- Header files ------------------------------------------------------*/
  31
  32 #include <errno.h>
  33 #include <stdarg.h>
  34 #include <stdio.h>
  35 #include <string.h>
  36
  37 #include <unistd.h>
  38 #include <dlfcn.h>
  39 #include <fcntl.h>
  40
  41 #include <sys/socket.h>
  42 #include <sys/stat.h>
  43 #include <sys/un.h>
  44
  45 #ifndef SUN_LEN
  46 #  define SUN_LEN (sun) \
  47         (strlen((sun)->sun_path) + offsetof(struct sockaddr_un, sun_path))
  48 #endif
  49
  50 /*----- Import the real versions of functions -----------------------------*/
  51
  52 /* The list of functions to immport. */
  53 #define IMPORTS(_)                                                      \
  54   _(open, int, (const char *, int, ...))                                \
  55   _(open64, int, (const char *, int, ...))                              \
  56   _(fopen, FILE *, (const char *, const char *))                        \
  57   _(freopen, FILE *, (const char *, const char *, FILE *))
  58
  59 /* Function pointers to set up. */
  60 #define DECL(imp, ret, args) static ret (*real_##imp) args;
  61 IMPORTS(DECL)
  62 #undef DECL
  63
  64 /* Import the system calls. */
  65 static void import(void)
  66 {
  67 #define IMPORT(imp, ret, args)                                          \
  68     real_##imp = (ret (*)args)dlsym(RTLD_NEXT, #imp);
  69   IMPORTS(IMPORT)
  70 #undef IMPORT
  71 }
  72 /*----- Utilities ---------------------------------------------------------*/
  73
  74 /* Socket address casts */
  75 #define SA(sa) ((struct sockaddr *)(sa))
  76
  77 /* Preservation of error status */
  78 #define PRESERVING_ERRNO(body) do {                                     \
  79   int _err = errno; { body } errno = _err;                              \
  80 } while (0)
  81
  82 /*----- Connecting to Unix-domain sockets ---------------------------------*/
  83
  84 /* If FN refers to a Unix-domain socket, connect to it, stash the socket
  85  * (or -1 on error) in *FDP, and return 1.  Otherwise return 0.
  86  */
  87 static int maybe_connect(const char *fn, int *fdp)
  88 {
  89   int fd;
  90   struct sockaddr_un sun;
  91   struct stat st;
  92
  93   if (stat(fn, &st) || !S_ISSOCK(st.st_mode))
  94     return (0);
  95   *fdp = -1;
  96   if (strlen(fn) >= sizeof(sun.sun_path)) {
  97     errno = EINVAL;
  98     return (1);
  99   }
 100   strncpy(sun.sun_path, fn, sizeof(sun.sun_path));
 101   sun.sun_family = AF_UNIX;
 102   if ((fd = socket(PF_UNIX, SOCK_STREAM, 0)) < 0 ||
 103       connect(fd, SA(&sun), SUN_LEN(&sun))) {
 104     PRESERVING_ERRNO( if (fd >= 0) close(fd); );
 105     return (1);
 106   }
 107   *fdp = fd;
 108   return (1);
 109 }
 110
 111 /*----- Intercepted system calls ------------------------------------------*/
 112
 113 /* Create an open(2)-like function OPEN. */
 114 #define OPEN_VENEER(open)                                               \
 115   int open(const char *fn, int how, ...)                                \
 116   {                                                                     \
 117     int mode = 0;                                                       \
 118     int fd;                                                             \
 119     va_list ap;                                                         \
 120                                                                         \
 121     PRESERVING_ERRNO({                                                  \
 122       if (how & O_CREAT)                                                \
 123         { va_start(ap, how); mode = va_arg(ap, int); va_end(ap); }      \
 124       if (!maybe_connect(fn, &fd)) fd = real_##open(fn, how, mode);     \
 125       if (fd < 0) return (-1);                                          \
 126     });                                                                 \
 127     return (fd);                                                        \
 128   }
 129
 130 /* open(2) and open64(2). */
 131 OPEN_VENEER(open)
 132 OPEN_VENEER(open64)
 133
 134 FILE *fopen(const char *fn, const char *how)
 135 {
 136   int fd;
 137   FILE *fp = 0;
 138
 139   PRESERVING_ERRNO({
 140     if (!maybe_connect(fn, &fd))
 141       fp = real_fopen(fn, how);
 142     else if (fd >= 0 && (fp = fdopen(fd, how)) == 0)
 143       PRESERVING_ERRNO( close(fd); );
 144   });
 145   return (fp);
 146 }
 147
 148 FILE *freopen(const char *fn, const char *how, FILE *fp)
 149 {
 150   int fd;
 151
 152   PRESERVING_ERRNO({
 153     if (!maybe_connect(fn, &fd))
 154       fp = real_freopen(fn, how, fp);
 155     else if (fd >= 0) {
 156       if (fflush(fp) || dup2(fd, fileno(fp))) fp = 0;
 157       PRESERVING_ERRNO( close(fd); );
 158     }
 159   });
 160   return (fp);
 161 }
 162
 163 /*----- Initialization ----------------------------------------------------*/
 164
 165 static void setup(void) __attribute__((constructor));
 166 static void setup(void)
 167 {
 168   PRESERVING_ERRNO({
 169     import();
 170   });
 171 }
 172
 173 /*----- That's all, folks -------------------------------------------------*/