glibc/libio/tst-sprintf-ub.c

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Set behavior of sprintf-like functions with overlapping source and destination According to ISO C99, passing the same buffer as source and destination to sprintf, snprintf, vsprintf, or vsnprintf has undefined behavior. Until the commit commit 4e2f43f842ef5e253cc23383645adbaa03cedb86 Author: Zack Weinberg <zackw@panix.com> Date: Wed Mar 7 14:32:03 2018 -0500 Use PRINTF_FORTIFY instead of _IO_FLAGS2_FORTIFY (bug 11319) a call to sprintf or vsprintf with overlapping buffers, for instance vsprintf (buf, "%sTEXT", buf), would append `TEXT' into buf, while a call to snprintf or vsnprintf would override the contents of buf. After the aforementioned commit, the behavior of sprintf and vsprintf changed (so that they also override the contents of buf). This patch reverts this behavioral change, because it will likely break applications that rely on the previous behavior, even though it is undefined by ISO C. As noted by Szabolcs Nagy, this is used in SPEC2017 507.cactuBSSN_r/src/PUGH/PughUtils.c: sprintf(mess," Size:"); for (i=0;i<dim+1;i++) { sprintf(mess,"%s %d",mess,pughGH->GFExtras[dim]->nsize[i]); } More important to notice is the fact that the overwriting of the destination buffer is not the only behavior affected by the refactoring. Before the refactoring, sprintf and vsprintf would use _IO_str_jumps, whereas __sprintf_chk and __vsprintf_chk would use _IO_str_chk_jumps. After the refactoring, all use _IO_str_chk_jumps, which would make sprintf and vsprintf report buffer overflows and terminate the program. This patch also reverts this behavior, by installing the appropriate jump table for each *sprintf functions. Apart from reverting the changes, this patch adds a test case that has the old behavior hardcoded, so that regressions are noticed if something else unintentionally changes the behavior. Tested for powerpc64le.
2018-12-19 21:01:14 +01:00
/* Test the sprintf (buf, "%s", buf) does not override buf.
Copyright (C) 2019 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <support/check.h>
enum
{
FUNCTION_FIRST,
FUNCTION_SPRINTF = FUNCTION_FIRST,
FUNCTION_SNPRINF,
FUNCTION_VSPRINTF,
FUNCTION_VSNPRINTF,
FUNCTION_LAST
};
static void
do_one_test (int function, char *buf, ...)
{
va_list args;
char *arg;
/* Expected results for fortified and non-fortified sprintf. */
#if defined _FORTIFY_SOURCE && _FORTIFY_SOURCE > 1
const char *expected = "CD";
#else
const char *expected = "ABCD";
#endif
va_start (args, buf);
arg = va_arg (args, char *);
va_end (args);
switch (function)
{
/* The regular sprintf and vsprintf functions do not override the
destination buffer, even if source and destination overlap. */
case FUNCTION_SPRINTF:
sprintf (buf, "%sCD", buf);
TEST_COMPARE_STRING (buf, expected);
break;
case FUNCTION_VSPRINTF:
va_start (args, buf);
vsprintf (arg, "%sCD", args);
TEST_COMPARE_STRING (arg, expected);
va_end (args);
break;
/* On the other hand, snprint and vsnprint override overlapping
source and destination buffers. */
case FUNCTION_SNPRINF:
snprintf (buf, 3, "%sCD", buf);
TEST_COMPARE_STRING (buf, "CD");
break;
case FUNCTION_VSNPRINTF:
va_start (args, buf);
vsnprintf (arg, 3, "%sCD", args);
TEST_COMPARE_STRING (arg, "CD");
va_end (args);
break;
default:
support_record_failure ();
}
}
static int
do_test (void)
{
char buf[8];
int i;
/* For each function in the enum do:
- reset the buffer to the initial state "AB";
- call the function with buffer as source and destination;
- check for the desired behavior. */
for (i = FUNCTION_FIRST; i < FUNCTION_LAST; i++)
{
strncpy (buf, "AB", 3);
do_one_test (i, buf, buf);
}
return 0;
}
#include <support/test-driver.c>