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commit 5bd80bfe9ca0d955bfbbc002781bc7b01b6bcb06
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Author: Paul Pluzhnikov <ppluzhnikov@google.com>
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Date: Fri Feb 6 00:30:42 2015 -0500
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CVE-2015-1472: wscanf allocates too little memory
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BZ #16618
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Under certain conditions wscanf can allocate too little memory for the
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to-be-scanned arguments and overflow the allocated buffer. The
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implementation now correctly computes the required buffer size when
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using malloc.
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A regression test was added to tst-sscanf.
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--- glibc-2.17-c758a686/stdio-common/vfscanf.c 2012-12-24 22:02:13.000000000 -0500
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+++ glibc-2.17-c758a686/stdio-common/vfscanf.c 2015-05-28 14:01:58.512816390 -0400
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@@ -272,9 +272,10 @@
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if (__builtin_expect (wpsize == wpmax, 0)) \
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{ \
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CHAR_T *old = wp; \
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- size_t newsize = (UCHAR_MAX + 1 > 2 * wpmax \
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- ? UCHAR_MAX + 1 : 2 * wpmax); \
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- if (use_malloc || !__libc_use_alloca (newsize)) \
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+ bool fits = __glibc_likely (wpmax <= SIZE_MAX / sizeof (CHAR_T) / 2); \
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+ size_t wpneed = MAX (UCHAR_MAX + 1, 2 * wpmax); \
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+ size_t newsize = fits ? wpneed * sizeof (CHAR_T) : SIZE_MAX; \
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+ if (!__libc_use_alloca (newsize)) \
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{ \
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wp = realloc (use_malloc ? wp : NULL, newsize); \
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if (wp == NULL) \
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@@ -286,14 +287,13 @@
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} \
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if (! use_malloc) \
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MEMCPY (wp, old, wpsize); \
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- wpmax = newsize; \
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+ wpmax = wpneed; \
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use_malloc = true; \
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} \
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else \
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{ \
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size_t s = wpmax * sizeof (CHAR_T); \
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- wp = (CHAR_T *) extend_alloca (wp, s, \
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- newsize * sizeof (CHAR_T)); \
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+ wp = (CHAR_T *) extend_alloca (wp, s, newsize); \
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wpmax = s / sizeof (CHAR_T); \
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if (old != NULL) \
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MEMCPY (wp, old, wpsize); \
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--- glibc-2.17-c758a686/stdio-common/tst-sscanf.c 2012-12-24 22:02:13.000000000 -0500
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+++ glibc-2.17-c758a686/stdio-common/tst-sscanf.c 2015-06-03 13:56:10.883924259 -0400
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@@ -196,5 +196,38 @@
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}
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}
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+ /* BZ #16618
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+ The test will segfault during SSCANF if the buffer overflow
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+ is not fixed. The size of `s` is such that it forces the use
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+ of malloc internally and this triggers the incorrect computation.
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+ Thus the value for SIZE is arbitrariy high enough that malloc
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+ is used. */
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+ {
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+#define SIZE 131072
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+ CHAR *s = malloc ((SIZE + 1) * sizeof (*s));
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+ if (s == NULL)
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+ abort ();
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+ for (size_t i = 0; i < SIZE; i++)
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+ s[i] = L('0');
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+ s[SIZE] = L('\0');
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+ int i = 42;
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+ /* Scan multi-digit zero into `i`. */
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+ if (SSCANF (s, L("%d"), &i) != 1)
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+ {
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+ printf ("FAIL: bug16618: SSCANF did not read one input item.\n");
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+ result = 1;
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+ }
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+ if (i != 0)
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+ {
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+ printf ("FAIL: bug16618: Value of `i` was not zero as expected.\n");
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+ result = 1;
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+ }
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+ free (s);
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+ if (result != 1)
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+ printf ("PASS: bug16618: Did not crash.\n");
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+#undef SIZE
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+ }
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+
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+
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return result;
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}
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