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Fix integer overflows in internal memalign and malloc [BZ #22343] [BZ #22774]

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When posix_memalign is called with an alignment less than MALLOC_ALIGNMENT
and a requested size close to SIZE_MAX, it falls back to malloc code
(because the alignment of a block returned by malloc is sufficient to
satisfy the call).  In this case, an integer overflow in _int_malloc leads
to posix_memalign incorrectly returning successfully.

Upon fixing this and writing a somewhat thorough regression test, it was
discovered that when posix_memalign is called with an alignment larger than
MALLOC_ALIGNMENT (so it uses _int_memalign instead) and a requested size
close to SIZE_MAX, a different integer overflow in _int_memalign leads to
posix_memalign incorrectly returning successfully.

Both integer overflows affect other memory allocation functions that use
_int_malloc (one affected malloc in x86) or _int_memalign as well.

This commit fixes both integer overflows.  In addition to this, it adds a
regression test to guard against false successful allocations by the
following memory allocation functions when called with too-large allocation
sizes and, where relevant, various valid alignments:
malloc, realloc, calloc, reallocarray, memalign, posix_memalign,
aligned_alloc, valloc, and pvalloc.

(cherry picked from commit 8e448310d7)
This commit is contained in:
Arjun Shankar 2018-01-18 16:47:06 +00:00
parent bbabb868cd
commit 01ba6f5076
5 changed files with 297 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
ChangeLog
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@ -1,3 +1,16 @@
2018-01-18 Arjun Shankar <arjun@redhat.com>
[BZ #22343]
[BZ #22774]
CVE-2018-6485
CVE-2018-6551
* malloc/malloc.c (checked_request2size): call REQUEST_OUT_OF_RANGE
after padding.
(_int_memalign): check for integer overflow before calling
_int_malloc.
* malloc/tst-malloc-too-large.c: New test.
* malloc/Makefile: Add tst-malloc-too-large.
2018-01-19 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
[BZ #22685]

8
NEWS
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@ -63,6 +63,14 @@ Security related changes:
succeeds without returning an absolute path due to unexpected behaviour
of the Linux kernel getcwd syscall. Reported by halfdog.
CVE-2018-6485: The posix_memalign and memalign functions, when called with
an object size near the value of SIZE_MAX, would return a pointer to a
buffer which is too small, instead of NULL. Reported by Jakub Wilk.
CVE-2018-6551: The malloc function, when called with an object size near
the value of SIZE_MAX, would return a pointer to a buffer which is too
small, instead of NULL.
The following bugs are resolved with this release:
[16750] ldd: Never run file directly.

1
malloc/Makefile
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@ -35,6 +35,7 @@ tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \
tst-interpose-thread \
tst-alloc_buffer \
tst-malloc-tcache-leak \
tst-malloc-too-large \
tests-static := \
tst-interpose-static-nothread \

30
malloc/malloc.c
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@ -1231,14 +1231,21 @@ nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MINSIZE : \
((req) + SIZE_SZ + MALLOC_ALIGN_MASK) & ~MALLOC_ALIGN_MASK)
/* Same, except also perform argument check */
#define checked_request2size(req, sz) \
if (REQUEST_OUT_OF_RANGE (req)) { \
__set_errno (ENOMEM); \
return 0; \
} \
(sz) = request2size (req);
/* Same, except also perform an argument and result check. First, we check
that the padding done by request2size didn't result in an integer
overflow. Then we check (using REQUEST_OUT_OF_RANGE) that the resulting
size isn't so large that a later alignment would lead to another integer
overflow. */
#define checked_request2size(req, sz) \
({ \
(sz) = request2size (req); \
if (((sz) < (req)) \
|| REQUEST_OUT_OF_RANGE (sz)) \
{ \
__set_errno (ENOMEM); \
return 0; \
} \
})
/*
--------------- Physical chunk operations ---------------
@ -4691,6 +4698,13 @@ _int_memalign (mstate av, size_t alignment, size_t bytes)
*/
/* Check for overflow. */
if (nb > SIZE_MAX - alignment - MINSIZE)
{
__set_errno (ENOMEM);
return 0;
}
/* Call malloc with worst case padding to hit alignment. */
m = (char *) (_int_malloc (av, nb + alignment + MINSIZE));

253
malloc/tst-malloc-too-large.c Normal file
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@ -0,0 +1,253 @@
/* Test and verify that too-large memory allocations fail with ENOMEM.
Copyright (C) 2018 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/>. */
/* Bug 22375 reported a regression in malloc where if after malloc'ing then
free'ing a small block of memory, malloc is then called with a really
large size argument (close to SIZE_MAX): instead of returning NULL and
setting errno to ENOMEM, malloc incorrectly returns the previously
allocated block instead. Bug 22343 reported a similar case where
posix_memalign incorrectly returns successfully when called with an with
a really large size argument.
Both of these were caused by integer overflows in the allocator when it
was trying to pad the requested size to allow for book-keeping or
alignment. This test guards against such bugs by repeatedly allocating
and freeing small blocks of memory then trying to allocate various block
sizes larger than the memory bus width of 64-bit targets, or almost
as large as SIZE_MAX on 32-bit targets supported by glibc. In each case,
it verifies that such impossibly large allocations correctly fail. */
#include <stdlib.h>
#include <malloc.h>
#include <errno.h>
#include <stdint.h>
#include <sys/resource.h>
#include <libc-diag.h>
#include <support/check.h>
#include <unistd.h>
#include <sys/param.h>
/* This function prepares for each 'too-large memory allocation' test by
performing a small successful malloc/free and resetting errno prior to
the actual test. */
static void
test_setup (void)
{
void *volatile ptr = malloc (16);
TEST_VERIFY_EXIT (ptr != NULL);
free (ptr);
errno = 0;
}
/* This function tests each of:
- malloc (SIZE)
- realloc (PTR_FOR_REALLOC, SIZE)
- for various values of NMEMB:
- calloc (NMEMB, SIZE/NMEMB)
- calloc (SIZE/NMEMB, NMEMB)
- reallocarray (PTR_FOR_REALLOC, NMEMB, SIZE/NMEMB)
- reallocarray (PTR_FOR_REALLOC, SIZE/NMEMB, NMEMB)
and precedes each of these tests with a small malloc/free before it. */
static void
test_large_allocations (size_t size)
{
void * ptr_to_realloc;
test_setup ();
TEST_VERIFY (malloc (size) == NULL);
TEST_VERIFY (errno == ENOMEM);
ptr_to_realloc = malloc (16);
TEST_VERIFY_EXIT (ptr_to_realloc != NULL);
test_setup ();
TEST_VERIFY (realloc (ptr_to_realloc, size) == NULL);
TEST_VERIFY (errno == ENOMEM);
free (ptr_to_realloc);
for (size_t nmemb = 1; nmemb <= 8; nmemb *= 2)
if ((size % nmemb) == 0)
{
test_setup ();
TEST_VERIFY (calloc (nmemb, size / nmemb) == NULL);
TEST_VERIFY (errno == ENOMEM);
test_setup ();
TEST_VERIFY (calloc (size / nmemb, nmemb) == NULL);
TEST_VERIFY (errno == ENOMEM);
ptr_to_realloc = malloc (16);
TEST_VERIFY_EXIT (ptr_to_realloc != NULL);
test_setup ();
TEST_VERIFY (reallocarray (ptr_to_realloc, nmemb, size / nmemb) == NULL);
TEST_VERIFY (errno == ENOMEM);
free (ptr_to_realloc);
ptr_to_realloc = malloc (16);
TEST_VERIFY_EXIT (ptr_to_realloc != NULL);
test_setup ();
TEST_VERIFY (reallocarray (ptr_to_realloc, size / nmemb, nmemb) == NULL);
TEST_VERIFY (errno == ENOMEM);
free (ptr_to_realloc);
}
else
break;
}
static long pagesize;
/* This function tests the following aligned memory allocation functions
using several valid alignments and precedes each allocation test with a
small malloc/free before it:
memalign, posix_memalign, aligned_alloc, valloc, pvalloc. */
static void
test_large_aligned_allocations (size_t size)
{
/* ptr stores the result of posix_memalign but since all those calls
should fail, posix_memalign should never change ptr. We set it to
NULL here and later on we check that it remains NULL after each
posix_memalign call. */
void * ptr = NULL;
size_t align;
/* All aligned memory allocation functions expect an alignment that is a
power of 2. Given this, we test each of them with every valid
alignment from 1 thru PAGESIZE. */
for (align = 1; align <= pagesize; align *= 2)
{
test_setup ();
TEST_VERIFY (memalign (align, size) == NULL);
TEST_VERIFY (errno == ENOMEM);
/* posix_memalign expects an alignment that is a power of 2 *and* a
multiple of sizeof (void *). */
if ((align % sizeof (void *)) == 0)
{
test_setup ();
TEST_VERIFY (posix_memalign (&ptr, align, size) == ENOMEM);
TEST_VERIFY (ptr == NULL);
}
/* aligned_alloc expects a size that is a multiple of alignment. */
if ((size % align) == 0)
{
test_setup ();
TEST_VERIFY (aligned_alloc (align, size) == NULL);
TEST_VERIFY (errno == ENOMEM);
}
}
/* Both valloc and pvalloc return page-aligned memory. */
test_setup ();
TEST_VERIFY (valloc (size) == NULL);
TEST_VERIFY (errno == ENOMEM);
test_setup ();
TEST_VERIFY (pvalloc (size) == NULL);
TEST_VERIFY (errno == ENOMEM);
}
#define FOURTEEN_ON_BITS ((1UL << 14) - 1)
#define FIFTY_ON_BITS ((1UL << 50) - 1)
static int
do_test (void)
{
#if __WORDSIZE >= 64
/* This test assumes that none of the supported targets have an address
bus wider than 50 bits, and that therefore allocations for sizes wider
than 50 bits will fail. Here, we ensure that the assumption continues
to be true in the future when we might have address buses wider than 50
bits. */
struct rlimit alloc_size_limit
= {
.rlim_cur = FIFTY_ON_BITS,
.rlim_max = FIFTY_ON_BITS
};
setrlimit (RLIMIT_AS, &alloc_size_limit);
#endif /* __WORDSIZE >= 64 */
DIAG_PUSH_NEEDS_COMMENT;
#if __GNUC_PREREQ (7, 0)
/* GCC 7 warns about too-large allocations; here we want to test
that they fail. */
DIAG_IGNORE_NEEDS_COMMENT (7, "-Walloc-size-larger-than=");
#endif
/* Aligned memory allocation functions need to be tested up to alignment
size equivalent to page size, which should be a power of 2. */
pagesize = sysconf (_SC_PAGESIZE);
TEST_VERIFY_EXIT (powerof2 (pagesize));
/* Loop 1: Ensure that all allocations with SIZE close to SIZE_MAX, i.e.
in the range (SIZE_MAX - 2^14, SIZE_MAX], fail.
We can expect that this range of allocation sizes will always lead to
an allocation failure on both 64 and 32 bit targets, because:
1. no currently supported 64-bit target has an address bus wider than
50 bits -- and (2^64 - 2^14) is much wider than that;
2. on 32-bit targets, even though 2^32 is only 4 GB and potentially
addressable, glibc itself is more than 2^14 bytes in size, and
therefore once glibc is loaded, less than (2^32 - 2^14) bytes remain
available. */
for (size_t i = 0; i <= FOURTEEN_ON_BITS; i++)
{
test_large_allocations (SIZE_MAX - i);
test_large_aligned_allocations (SIZE_MAX - i);
}
#if __WORDSIZE >= 64
/* On 64-bit targets, we need to test a much wider range of too-large
sizes, so we test at intervals of (1 << 50) that allocation sizes
ranging from SIZE_MAX down to (1 << 50) fail:
The 14 MSBs are decremented starting from "all ON" going down to 1,
the 50 LSBs are "all ON" and then "all OFF" during every iteration. */
for (size_t msbs = FOURTEEN_ON_BITS; msbs >= 1; msbs--)
{
size_t size = (msbs << 50) | FIFTY_ON_BITS;
test_large_allocations (size);
test_large_aligned_allocations (size);
size = msbs << 50;
test_large_allocations (size);
test_large_aligned_allocations (size);
}
#endif /* __WORDSIZE >= 64 */
DIAG_POP_NEEDS_COMMENT;
return 0;
}
#include <support/test-driver.c>