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time_rz: fix heap buffer overflow vulnerability

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This issue has been assigned CVE-2017-7476 and was
detected with American Fuzzy Lop 2.41b run on the
coreutils date(1) program with ASAN enabled.

  ERROR: AddressSanitizer: heap-buffer-overflow on address 0x...
  WRITE of size 8 at 0x60d00000cff8 thread T0
  #1 0x443020 in extend_abbrs lib/time_rz.c:88
  #2 0x443356 in save_abbr lib/time_rz.c:155
  #3 0x44393f in localtime_rz lib/time_rz.c:290
  #4 0x41e4fe in parse_datetime2 lib/parse-datetime.y:1798

A minimized reproducer is the following 120 byte TZ value,
which goes beyond the value of ABBR_SIZE_MIN (119) on x86_64.
Extend the aa...b portion to overwrite more of the heap.

  date -d $(printf 'TZ="aaa%020daaaaaab%089d"')

localtime_rz and mktime_z were affected since commit 4bc76593.
parse_datetime was affected since commit 4e6e16b3f.

* lib/time_rz.c (save_abbr): Rearrange the calculation determining
whether there is enough buffer space available.  The rearrangement
ensures we're only dealing with positive numbers, thus avoiding
the problematic promotion of signed to unsigned causing an invalid
comparison when zone_copy is more than ABBR_SIZE_MIN bytes beyond
the start of the buffer.
* tests/test-parse-datetime.c (main): Add a test case written by
Paul Eggert, which overwrites enough of the heap so that
standard glibc will fail with "free(): invalid pointer"
without the patch applied.
Reported and analyzed at https://bugzilla.redhat.com/1444774
This commit is contained in:
Pádraig Brady
2017-04-24 01:43:36 -07:00
parent cff48ff751
commit 94e0157150
3 changed files with 44 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
tests/test-parse-datetime.c
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@@ -432,5 +432,21 @@ main (int argc _GL_UNUSED, char **argv)
ASSERT ( parse_datetime (&result, "TZ=\"\\\\\"", &now));
ASSERT ( parse_datetime (&result, "TZ=\"\\\"\"", &now));
/* Outlandishly-long time zone abbreviations should not cause problems. */
{
static char const bufprefix[] = "TZ=\"";
enum { tzname_len = 2000 };
static char const bufsuffix[] = "0\" 1970-01-01 01:02:03.123456789";
enum { bufsize = sizeof bufprefix - 1 + tzname_len + sizeof bufsuffix };
char buf[bufsize];
memcpy (buf, bufprefix, sizeof bufprefix - 1);
memset (buf + sizeof bufprefix - 1, 'X', tzname_len);
strcpy (buf + bufsize - sizeof bufsuffix, bufsuffix);
ASSERT (parse_datetime (&result, buf, &now));
LOG (buf, now, result);
ASSERT (result.tv_sec == 1 * 60 * 60 + 2 * 60 + 3
&& result.tv_nsec == 123456789);
}
return 0;
}