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Add assert for potential access beyond array bounds in m1np

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The mpexp code has an access into m1np:

  for (i=n-1; i>0; i--,n--) { if (m1np[i][p]+m2>0) break; }

which could break for p >= 18 or i >= 7.  Fortunately this code is
never called due to the way the exp function is implemented since
values having exponent less than -55 return 1.0.  Make sure that if it
gets called in future, it is trapped.
This commit is contained in:
Siddhesh Poyarekar 2013-01-02 11:33:11 +05:30
parent da08f647d5
commit 4d55b4e596
2 changed files with 20 additions and 4 deletions
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3
ChangeLog
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@ -1,5 +1,8 @@
2013-01-02 Siddhesh Poyarekar <siddhesh@redhat.com> 2013-01-02 Siddhesh Poyarekar <siddhesh@redhat.com>
* sysdeps/ieee754/dbl-64/mpexp.c (__mpexp): Add assert to
check access beyond bounds of m1np.
* sysdeps/ieee754/dbl-64/mpa.c [! NO__CONST]: New constant * sysdeps/ieee754/dbl-64/mpa.c [! NO__CONST]: New constant
MPTWO. MPTWO.
(__inv): Remove local variable MPTWO to use the global (__inv): Remove local variable MPTWO to use the global

21
sysdeps/ieee754/dbl-64/mpexp.c
View File

@ -31,6 +31,7 @@
#include "endian.h" #include "endian.h"
#include "mpa.h" #include "mpa.h"
#include "mpexp.h" #include "mpexp.h"
#include <assert.h>
#ifndef SECTION #ifndef SECTION
# define SECTION # define SECTION
@ -71,10 +72,22 @@ __mpexp(mp_no *x, mp_no *y, int p) {
for (i=2; i<=p; i++) { if (X[i]!=ZERO) break; } for (i=2; i<=p; i++) { if (X[i]!=ZERO) break; }
if (i==p+1) { m2--; a *= TWO; } if (i==p+1) { m2--; a *= TWO; }
} }
if ((m=m1+m2) <= 0) {
m=0; a=ONE; m = m1 + m2;
for (i=n-1; i>0; i--,n--) { if (m1np[i][p]+m2>0) break; } if (__glibc_unlikely (m <= 0))
} {
/* The m1np array which is used to determine if we can reduce the
polynomial expansion iterations, has only 18 elements. Besides,
numbers smaller than those required by p >= 18 should not come here
at all since the fast phase of exp returns 1.0 for anything less
than 2^-55. */
assert (p < 18);
m = 0;
a = ONE;
for (i = n - 1; i > 0; i--, n--)
if (m1np[i][p] + m2 > 0)
break;
}
/* Compute s=x*2**(-m). Put result in mps */ /* Compute s=x*2**(-m). Put result in mps */
__dbl_mp(a,&mpt1,p); __dbl_mp(a,&mpt1,p);