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From 5bd80bfe9ca0d955bfbbc002781bc7b01b6bcb06 Mon Sep 17 00:00:00 2001 |
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From: Paul Pluzhnikov <ppluzhnikov@google.com> |
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Date: Fri, 6 Feb 2015 00:30:42 -0500 |
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Subject: [PATCH] CVE-2015-1472: wscanf allocates too little memory |
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|
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BZ #16618 |
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|
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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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|
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A regression test was added to tst-sscanf. |
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--- |
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ChangeLog | 8 ++++++++ |
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NEWS | 24 +++++++++++++++--------- |
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stdio-common/tst-sscanf.c | 33 +++++++++++++++++++++++++++++++++ |
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stdio-common/vfscanf.c | 12 ++++++------ |
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4 files changed, 62 insertions(+), 15 deletions(-) |
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|
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#diff --git a/ChangeLog b/ChangeLog |
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#index 4916b03..d23d3ae 100644 |
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#--- a/ChangeLog |
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#+++ b/ChangeLog |
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#@@ -1,3 +1,11 @@ |
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#+2015-02-05 Paul Pluzhnikov <ppluzhnikov@google.com> |
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#+ |
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#+ [BZ #16618] |
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#+ * stdio-common/tst-sscanf.c (main): Test for buffer overflow. |
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#+ * stdio-common/vfscanf.c (_IO_vfscanf_internal): Compute needed |
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#+ size in bytes. Store needed elements in wpmax. Use needed size |
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#+ in bytes for extend_alloca. |
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#+ |
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# 2015-02-05 Carlos O'Donell <carlos@systemhalted.org> |
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# |
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# * manual/install.texi: Latest tested versions are GCC 4.9.2, |
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#diff --git a/NEWS b/NEWS |
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#index c91b9fc..617cdbb 100644 |
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#--- a/NEWS |
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#+++ b/NEWS |
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#@@ -10,15 +10,21 @@ Version 2.21 |
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# * The following bugs are resolved with this release: |
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# |
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# 6652, 10672, 12674, 12847, 12926, 13862, 14132, 14138, 14171, 14498, |
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#- 15215, 15378, 15884, 16009, 16418, 16191, 16469, 16576, 16617, 16619, |
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#- 16657, 16740, 16857, 17192, 17266, 17273, 17344, 17363, 17370, 17371, |
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#- 17411, 17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555, 17570, |
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#- 17571, 17572, 17573, 17574, 17582, 17583, 17584, 17585, 17589, 17594, |
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#- 17601, 17608, 17616, 17625, 17630, 17633, 17634, 17635, 17647, 17653, |
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#- 17657, 17658, 17664, 17665, 17668, 17682, 17702, 17717, 17719, 17722, |
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#- 17723, 17724, 17725, 17732, 17733, 17744, 17745, 17746, 17747, 17748, |
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#- 17775, 17777, 17780, 17781, 17782, 17791, 17793, 17796, 17797, 17801, |
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#- 17803, 17806, 17834, 17844, 17848, 17868, 17869, 17870, 17885, 17892. |
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#+ 15215, 15378, 15884, 16009, 16418, 16191, 16469, 16576, 16617, 16618, |
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#+ 16619, 16657, 16740, 16857, 17192, 17266, 17273, 17344, 17363, 17370, |
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#+ 17371, 17411, 17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555, |
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#+ 17570, 17571, 17572, 17573, 17574, 17582, 17583, 17584, 17585, 17589, |
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#+ 17594, 17601, 17608, 17616, 17625, 17630, 17633, 17634, 17635, 17647, |
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#+ 17653, 17657, 17658, 17664, 17665, 17668, 17682, 17702, 17717, 17719, |
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#+ 17722, 17723, 17724, 17725, 17732, 17733, 17744, 17745, 17746, 17747, |
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#+ 17748, 17775, 17777, 17780, 17781, 17782, 17791, 17793, 17796, 17797, |
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#+ 17801, 17803, 17806, 17834, 17844, 17848, 17868, 17869, 17870, 17885, |
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#+ 17892. |
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#+ |
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#+* CVE-2015-1472 Under certain conditions wscanf can allocate too little |
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#+ memory for the to-be-scanned arguments and overflow the allocated |
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#+ buffer. The implementation now correctly computes the required buffer |
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#+ size when using malloc. |
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# |
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# * A new semaphore algorithm has been implemented in generic C code for all |
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# machines. Previous custom assembly implementations of semaphore were |
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diff --git a/stdio-common/tst-sscanf.c b/stdio-common/tst-sscanf.c |
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index aece3f2..8a2eb9e 100644 |
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--- a/stdio-common/tst-sscanf.c |
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+++ b/stdio-common/tst-sscanf.c |
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@@ -233,5 +233,38 @@ main (void) |
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} |
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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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diff --git a/stdio-common/vfscanf.c b/stdio-common/vfscanf.c |
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index cd129a8..0e204e7 100644 |
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--- a/stdio-common/vfscanf.c |
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+++ b/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, |
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if (__glibc_unlikely (wpsize == wpmax)) \ |
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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 @@ _IO_vfscanf_internal (_IO_FILE *s, const char *format, _IO_va_list argptr, |
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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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-- |
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2.3.0 |
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