elf/dl-exception.c

   1 /* ld.so error exception allocation and deallocation.
   2    Copyright (C) 1995-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <ldsodefs.h>
  20 #include <limits.h>
  21 #include <stdarg.h>
  22 #include <stdbool.h>
  23 #include <stdint.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26
  27 /* This message we return as a last resort.  We define the string in a
  28    variable since we have to avoid freeing it and so have to enable
  29    a pointer comparison.  See below and in dlfcn/dlerror.c.  */
  30 static const char _dl_out_of_memory[] = "out of memory";
  31
  32 /* Dummy allocation object used if allocating the message buffer
  33    fails.  */
  34 static void
  35 oom_exception (struct dl_exception *exception)
  36 {
  37   exception->objname = "";
  38   exception->errstring = _dl_out_of_memory;
  39   exception->message_buffer = NULL;
  40 }
  41
  42 static void
  43 __attribute__ ((noreturn))
  44 length_mismatch (void)
  45 {
  46   _dl_fatal_printf ("Fatal error: "
  47                     "length accounting in _dl_exception_create_format\n");
  48 }
  49
  50 /* Adjust the message buffer to indicate whether it is possible to
  51    free it.  EXCEPTION->errstring must be a potentially deallocatable
  52    pointer.  */
  53 static void
  54 adjust_message_buffer (struct dl_exception *exception)
  55 {
  56   /* If the main executable is relocated it means the libc's malloc
  57      is used.  */
  58   bool malloced = true;
  59 #ifdef SHARED
  60   malloced = (GL(dl_ns)[LM_ID_BASE]._ns_loaded != NULL
  61               && (GL(dl_ns)[LM_ID_BASE]._ns_loaded->l_relocated != 0));
  62 #endif
  63   if (malloced)
  64     exception->message_buffer = (char *) exception->errstring;
  65   else
  66     exception->message_buffer = NULL;
  67 }
  68
  69 void
  70 _dl_exception_create (struct dl_exception *exception, const char *objname,
  71                       const char *errstring)
  72 {
  73   if (objname == NULL)
  74     objname = "";
  75   size_t len_objname = strlen (objname) + 1;
  76   size_t len_errstring = strlen (errstring) + 1;
  77   char *errstring_copy = malloc (len_objname + len_errstring);
  78   if (errstring_copy != NULL)
  79     {
  80       /* Make a copy of the object file name and the error string.  */
  81       exception->objname = memcpy (__mempcpy (errstring_copy,
  82                                               errstring, len_errstring),
  83                                    objname, len_objname);
  84       exception->errstring = errstring_copy;
  85       adjust_message_buffer (exception);
  86     }
  87   else
  88     oom_exception (exception);
  89 }
  90 rtld_hidden_def (_dl_exception_create)
  91
  92 void
  93 _dl_exception_create_format (struct dl_exception *exception, const char *objname,
  94                              const char *fmt, ...)
  95 {
  96   if (objname == NULL)
  97     objname = "";
  98   size_t len_objname = strlen (objname) + 1;
  99   /* Compute the length of the result.  Include room for two NUL
 100      bytes.  */
 101   size_t length = len_objname + 1;
 102   {
 103     va_list ap;
 104     va_start (ap, fmt);
 105     for (const char *p = fmt; *p != '\0'; ++p)
 106       if (*p == '%')
 107         {
 108           ++p;
 109           switch (*p)
 110             {
 111             case 's':
 112               length += strlen (va_arg (ap, const char *));
 113               break;
 114             default:
 115               /* Assumed to be '%'.  */
 116               ++length;
 117               break;
 118             }
 119         }
 120       else
 121         ++length;
 122     va_end (ap);
 123   }
 124
 125   if (length > PTRDIFF_MAX)
 126     {
 127       oom_exception (exception);
 128       return;
 129     }
 130   char *errstring = malloc (length);
 131   if (errstring == NULL)
 132     {
 133       oom_exception (exception);
 134       return;
 135     }
 136   exception->errstring = errstring;
 137   adjust_message_buffer (exception);
 138
 139   /* Copy the error message to errstring.  */
 140   {
 141     /* Next byte to be written in errstring.  */
 142     char *wptr = errstring;
 143     /* End of the allocated string.  */
 144     char *const end = errstring + length;
 145
 146     va_list ap;
 147     va_start (ap, fmt);
 148
 149     for (const char *p = fmt; *p != '\0'; ++p)
 150       if (*p == '%')
 151         {
 152           ++p;
 153           switch (*p)
 154             {
 155             case 's':
 156               {
 157                 const char *ptr = va_arg (ap, const char *);
 158                 size_t len_ptr = strlen (ptr);
 159                 if (len_ptr > end - wptr)
 160                   length_mismatch ();
 161                 wptr = __mempcpy (wptr, ptr, len_ptr);
 162               }
 163               break;
 164             case '%':
 165               if (wptr == end)
 166                 length_mismatch ();
 167               *wptr = '%';
 168               ++wptr;
 169               break;
 170             default:
 171               _dl_fatal_printf ("Fatal error:"
 172                                 " invalid format in exception string\n");
 173             }
 174         }
 175       else
 176         {
 177           if (wptr == end)
 178             length_mismatch ();
 179           *wptr = *p;
 180           ++wptr;
 181         }
 182
 183     if (wptr == end)
 184       length_mismatch ();
 185     *wptr = '\0';
 186     ++wptr;
 187     if (len_objname != end - wptr)
 188       length_mismatch ();
 189     exception->objname = memcpy (wptr, objname, len_objname);
 190   }
 191 }
 192 rtld_hidden_def (_dl_exception_create_format)
 193
 194 void
 195 _dl_exception_free (struct dl_exception *exception)
 196 {
 197   free (exception->message_buffer);
 198   exception->objname = NULL;
 199   exception->errstring = NULL;
 200   exception->message_buffer = NULL;
 201 }
 202 rtld_hidden_def (_dl_exception_free)