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From: Paul Pluzhnikov <ppluzhnikov@google.com>
Date: Fri, 6 Feb 2015 00:30:42 -0500
Subject: [PATCH] CVE-2015-1472: wscanf allocates too little memory
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.
---
stdio-common/tst-sscanf.c | 33 +++++++++++++++++++++++++++++++++
stdio-common/vfscanf.c | 12 ++++++------
2 files changed, 39 insertions(+), 6 deletions(-)
diff --git a/stdio-common/tst-sscanf.c b/stdio-common/tst-sscanf.c
index 9fef93a53578..6394fe1cccd1 100644
--- a/stdio-common/tst-sscanf.c
+++ b/stdio-common/tst-sscanf.c
@@ -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;
}
diff --git a/stdio-common/vfscanf.c b/stdio-common/vfscanf.c
index e0d224530cc6..a4f06b44e576 100644
--- a/stdio-common/vfscanf.c
+++ b/stdio-common/vfscanf.c
@@ -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); \
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