libio/iovsprintf.c

   1 /* Copyright (C) 1993-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.
  17
  18    As a special exception, if you link the code in this file with
  19    files compiled with a GNU compiler to produce an executable,
  20    that does not cause the resulting executable to be covered by
  21    the GNU Lesser General Public License.  This exception does not
  22    however invalidate any other reasons why the executable file
  23    might be covered by the GNU Lesser General Public License.
  24    This exception applies to code released by its copyright holders
  25    in files containing the exception.  */
  26
  27 #include "libioP.h"
  28
  29 #include <printf.h>
  30 #include <stdint.h>
  31 #include <printf_buffer.h>
  32
  33 int
  34 __vsprintf_internal (char *string, size_t maxlen,
  35                      const char *format, va_list args,
  36                      unsigned int mode_flags)
  37 {
  38   struct __printf_buffer buf;
  39
  40   /* When called from fortified sprintf/vsprintf, erase the destination
  41      buffer and try to detect overflows.  When called from regular
  42      sprintf/vsprintf, do not erase the destination buffer, because
  43      known user code relies on this behavior (even though its undefined
  44      by ISO C), nor try to detect overflows.  */
  45   if ((mode_flags & PRINTF_CHK) != 0)
  46     {
  47       string[0] = '\0';
  48       /* In some cases, __sprintf_chk is called with an unknown buffer
  49          size (the special value -1).  Prevent pointer wraparound in
  50          this case and saturate to the end of the address space.  */
  51       uintptr_t end;
  52       if (__builtin_add_overflow ((uintptr_t) string, maxlen, &end))
  53         end = -1;
  54       __printf_buffer_init_end (&buf, string, (char *) end,
  55                             __printf_buffer_mode_sprintf_chk);
  56     }
  57   else
  58     /* Use end of address space.  */
  59     __printf_buffer_init_end (&buf, string, (char *) ~(uintptr_t) 0,
  60                               __printf_buffer_mode_sprintf);
  61
  62   __printf_buffer (&buf, format, args, mode_flags);
  63
  64   /* Write the NUL terminator if there is room.  Do not use the putc
  65      operation to avoid overflowing the character write count.  */
  66   if ((mode_flags & PRINTF_CHK) != 0 && buf.write_ptr == buf.write_end)
  67     __chk_fail ();
  68   *buf.write_ptr = '\0';
  69
  70   return __printf_buffer_done (&buf);
  71 }
  72
  73 int
  74 __vsprintf (char *string, const char *format, va_list args)
  75 {
  76   return __vsprintf_internal (string, -1, format, args, 0);
  77 }
  78
  79 ldbl_strong_alias (__vsprintf, _IO_vsprintf)
  80 ldbl_weak_alias (__vsprintf, vsprintf)