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CVE-2015-1472: wscanf allocates too little memory

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BZ #16618

Under certain conditions wscanf can allocate too little memory for the
to-be-scanned arguments and overflow the allocated buffer.  The
implementation now correctly computes the required buffer size when
using malloc.

A regression test was added to tst-sscanf.
This commit is contained in:
Paul Pluzhnikov 2015-02-06 00:30:42 -05:00 committed by Carlos O'Donell
parent 04cb913ddf
commit 5bd80bfe9c
4 changed files with 62 additions and 15 deletions
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8
ChangeLog
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@ -1,3 +1,11 @@
2015-02-05 Paul Pluzhnikov <ppluzhnikov@google.com>
[BZ #16618]
* stdio-common/tst-sscanf.c (main): Test for buffer overflow.
* stdio-common/vfscanf.c (_IO_vfscanf_internal): Compute needed
size in bytes. Store needed elements in wpmax. Use needed size
in bytes for extend_alloca.
2015-02-05 Carlos O'Donell <carlos@systemhalted.org>
* manual/install.texi: Latest tested versions are GCC 4.9.2,

24
NEWS
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@ -10,15 +10,21 @@ Version 2.21
* The following bugs are resolved with this release:
6652, 10672, 12674, 12847, 12926, 13862, 14132, 14138, 14171, 14498,
15215, 15378, 15884, 16009, 16418, 16191, 16469, 16576, 16617, 16619,
16657, 16740, 16857, 17192, 17266, 17273, 17344, 17363, 17370, 17371,
17411, 17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555, 17570,
17571, 17572, 17573, 17574, 17582, 17583, 17584, 17585, 17589, 17594,
17601, 17608, 17616, 17625, 17630, 17633, 17634, 17635, 17647, 17653,
17657, 17658, 17664, 17665, 17668, 17682, 17702, 17717, 17719, 17722,
17723, 17724, 17725, 17732, 17733, 17744, 17745, 17746, 17747, 17748,
17775, 17777, 17780, 17781, 17782, 17791, 17793, 17796, 17797, 17801,
17803, 17806, 17834, 17844, 17848, 17868, 17869, 17870, 17885, 17892.
15215, 15378, 15884, 16009, 16418, 16191, 16469, 16576, 16617, 16618,
16619, 16657, 16740, 16857, 17192, 17266, 17273, 17344, 17363, 17370,
17371, 17411, 17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555,
17570, 17571, 17572, 17573, 17574, 17582, 17583, 17584, 17585, 17589,
17594, 17601, 17608, 17616, 17625, 17630, 17633, 17634, 17635, 17647,
17653, 17657, 17658, 17664, 17665, 17668, 17682, 17702, 17717, 17719,
17722, 17723, 17724, 17725, 17732, 17733, 17744, 17745, 17746, 17747,
17748, 17775, 17777, 17780, 17781, 17782, 17791, 17793, 17796, 17797,
17801, 17803, 17806, 17834, 17844, 17848, 17868, 17869, 17870, 17885,
17892.
* CVE-2015-1472 Under certain conditions wscanf can allocate too little
memory for the to-be-scanned arguments and overflow the allocated
buffer. The implementation now correctly computes the required buffer
size when using malloc.
* A new semaphore algorithm has been implemented in generic C code for all
machines. Previous custom assembly implementations of semaphore were

33
stdio-common/tst-sscanf.c
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@ -233,5 +233,38 @@ main (void)
}
}
/* BZ #16618
The test will segfault during SSCANF if the buffer overflow
is not fixed. The size of `s` is such that it forces the use
of malloc internally and this triggers the incorrect computation.
Thus the value for SIZE is arbitrariy high enough that malloc
is used. */
{
#define SIZE 131072
CHAR *s = malloc ((SIZE + 1) * sizeof (*s));
if (s == NULL)
abort ();
for (size_t i = 0; i < SIZE; i++)
s[i] = L('0');
s[SIZE] = L('\0');
int i = 42;
/* Scan multi-digit zero into `i`. */
if (SSCANF (s, L("%d"), &i) != 1)
{
printf ("FAIL: bug16618: SSCANF did not read one input item.\n");
result = 1;
}
if (i != 0)
{
printf ("FAIL: bug16618: Value of `i` was not zero as expected.\n");
result = 1;
}
free (s);
if (result != 1)
printf ("PASS: bug16618: Did not crash.\n");
#undef SIZE
}
return result;
}

12
stdio-common/vfscanf.c
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@ -272,9 +272,10 @@ _IO_vfscanf_internal (_IO_FILE *s, const char *format, _IO_va_list argptr,
if (__glibc_unlikely (wpsize == wpmax)) \
{ \
CHAR_T *old = wp; \
size_t newsize = (UCHAR_MAX + 1 > 2 * wpmax \
? UCHAR_MAX + 1 : 2 * wpmax); \
if (use_malloc || !__libc_use_alloca (newsize)) \
bool fits = __glibc_likely (wpmax <= SIZE_MAX / sizeof (CHAR_T) / 2); \
size_t wpneed = MAX (UCHAR_MAX + 1, 2 * wpmax); \
size_t newsize = fits ? wpneed * sizeof (CHAR_T) : SIZE_MAX; \
if (!__libc_use_alloca (newsize)) \
{ \
wp = realloc (use_malloc ? wp : NULL, newsize); \
if (wp == NULL) \
@ -286,14 +287,13 @@ _IO_vfscanf_internal (_IO_FILE *s, const char *format, _IO_va_list argptr,
} \
if (! use_malloc) \
MEMCPY (wp, old, wpsize); \
wpmax = newsize; \
wpmax = wpneed; \
use_malloc = true; \
} \
else \
{ \
size_t s = wpmax * sizeof (CHAR_T); \
wp = (CHAR_T *) extend_alloca (wp, s, \
newsize * sizeof (CHAR_T)); \
wp = (CHAR_T *) extend_alloca (wp, s, newsize); \
wpmax = s / sizeof (CHAR_T); \
if (old != NULL) \
MEMCPY (wp, old, wpsize); \