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 /*----- Import the real versions of functions -----------------------------*/
  46
  47 /* The list of functions to immport. */
  48 #define IMPORTS(_)                                                      \
  49   _(open, int, (const char *, int, ...))                                \
  50   _(open64, int, (const char *, int, ...))                              \
  51   _(fopen, FILE *, (const char *, const char *))                        \
  52   _(freopen, FILE *, (const char *, const char *, FILE *))
  53
  54 /* Function pointers to set up. */
  55 #define DECL(imp, ret, args) static ret (*real_##imp) args;
  56 IMPORTS(DECL)
  57 #undef DECL
  58
  59 /* Import the system calls. */
  60 static void import(void)
  61 {
  62 #define IMPORT(imp, ret, args)                                          \
  63     real_##imp = (ret (*)args)dlsym(RTLD_NEXT, #imp);
  64   IMPORTS(IMPORT)
  65 #undef IMPORT
  66 }
  67 /*----- Utilities ---------------------------------------------------------*/
  68
  69 /* Socket address casts */
  70 #define SA(sa) ((struct sockaddr *)(sa))
  71
  72 /* Preservation of error status */
  73 #define PRESERVING_ERRNO(body) do {                                     \
  74   int _err = errno; { body } errno = _err;                              \
  75 } while (0)
  76
  77 /*----- Connecting to Unix-domain sockets ---------------------------------*/
  78
  79 /* If FN refers to a Unix-domain socket, connect to it, stash the socket
  80  * (or -1 on error) in *FDP, and return 1.  Otherwise return 0.
  81  */
  82 static int maybe_connect(const char *fn, int *fdp)
  83 {
  84   int fd;
  85   struct sockaddr_un sun;
  86   struct stat st;
  87
  88   if (stat(fn, &st) || !S_ISSOCK(st.st_mode))
  89     return (0);
  90   *fdp = -1;
  91   if (strlen(fn) >= sizeof(sun.sun_path)) {
  92     errno = EINVAL;
  93     return (1);
  94   }
  95   strncpy(sun.sun_path, fn, sizeof(sun.sun_path));
  96   sun.sun_family = AF_UNIX;
  97   if ((fd = socket(PF_UNIX, SOCK_STREAM, 0)) < 0 ||
  98       connect(fd, SA(&sun), SUN_LEN(&sun))) {
  99     PRESERVING_ERRNO( if (fd >= 0) close(fd); );
 100     return (1);
 101   }
 102   *fdp = fd;
 103   return (1);
 104 }
 105
 106 /*----- Intercepted system calls ------------------------------------------*/
 107
 108 /* Create an open(2)-like function OPEN. */
 109 #define OPEN_VENEER(open)                                               \
 110   int open(const char *fn, int how, ...)                                \
 111   {                                                                     \
 112     int mode = 0;                                                       \
 113     int fd;                                                             \
 114     va_list ap;                                                         \
 115                                                                         \
 116     PRESERVING_ERRNO({                                                  \
 117       if (how & O_CREAT)                                                \
 118         { va_start(ap, how); mode = va_arg(ap, int); va_end(ap); }      \
 119       if (!maybe_connect(fn, &fd)) fd = real_##open(fn, how, mode);     \
 120       if (fd < 0) return (-1);                                          \
 121     });                                                                 \
 122     return (fd);                                                        \
 123   }
 124
 125 /* open(2) and open64(2). */
 126 OPEN_VENEER(open)
 127 OPEN_VENEER(open64)
 128
 129 FILE *fopen(const char *fn, const char *how)
 130 {
 131   int fd;
 132   FILE *fp = 0;
 133
 134   PRESERVING_ERRNO({
 135     if (!maybe_connect(fn, &fd))
 136       fp = real_fopen(fn, how);
 137     else if (fd >= 0 && (fp = fdopen(fd, how)) == 0)
 138       PRESERVING_ERRNO( close(fd); );
 139   });
 140   return (fp);
 141 }
 142
 143 FILE *freopen(const char *fn, const char *how, FILE *fp)
 144 {
 145   int fd;
 146
 147   PRESERVING_ERRNO({
 148     if (!maybe_connect(fn, &fd))
 149       fp = real_freopen(fn, how, fp);
 150     else if (fd >= 0) {
 151       if (fflush(fp) || dup2(fd, fileno(fp))) fp = 0;
 152       PRESERVING_ERRNO( close(fd); );
 153     }
 154   });
 155   return (fp);
 156 }
 157
 158 /*----- Initialization ----------------------------------------------------*/
 159
 160 static void setup(void) __attribute__((constructor));
 161 static void setup(void)
 162 {
 163   PRESERVING_ERRNO({
 164     import();
 165   });
 166 }
 167
 168 /*----- That's all, folks -------------------------------------------------*/