linux/lib/mpi/mpi-pow.c
Andrey Ryabinin f5527fffff mpi: Fix NULL ptr dereference in mpi_powm() [ver #3]
This fixes CVE-2016-8650.

If mpi_powm() is given a zero exponent, it wants to immediately return
either 1 or 0, depending on the modulus.  However, if the result was
initalised with zero limb space, no limbs space is allocated and a
NULL-pointer exception ensues.

Fix this by allocating a minimal amount of limb space for the result when
the 0-exponent case when the result is 1 and not touching the limb space
when the result is 0.

This affects the use of RSA keys and X.509 certificates that carry them.

BUG: unable to handle kernel NULL pointer dereference at           (null)
IP: [<ffffffff8138ce5d>] mpi_powm+0x32/0x7e6
PGD 0
Oops: 0002 [#1] SMP
Modules linked in:
CPU: 3 PID: 3014 Comm: keyctl Not tainted 4.9.0-rc6-fscache+ #278
Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
task: ffff8804011944c0 task.stack: ffff880401294000
RIP: 0010:[<ffffffff8138ce5d>]  [<ffffffff8138ce5d>] mpi_powm+0x32/0x7e6
RSP: 0018:ffff880401297ad8  EFLAGS: 00010212
RAX: 0000000000000000 RBX: ffff88040868bec0 RCX: ffff88040868bba0
RDX: ffff88040868b260 RSI: ffff88040868bec0 RDI: ffff88040868bee0
RBP: ffff880401297ba8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000047 R11: ffffffff8183b210 R12: 0000000000000000
R13: ffff8804087c7600 R14: 000000000000001f R15: ffff880401297c50
FS:  00007f7a7918c700(0000) GS:ffff88041fb80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000401250000 CR4: 00000000001406e0
Stack:
 ffff88040868bec0 0000000000000020 ffff880401297b00 ffffffff81376cd4
 0000000000000100 ffff880401297b10 ffffffff81376d12 ffff880401297b30
 ffffffff81376f37 0000000000000100 0000000000000000 ffff880401297ba8
Call Trace:
 [<ffffffff81376cd4>] ? __sg_page_iter_next+0x43/0x66
 [<ffffffff81376d12>] ? sg_miter_get_next_page+0x1b/0x5d
 [<ffffffff81376f37>] ? sg_miter_next+0x17/0xbd
 [<ffffffff8138ba3a>] ? mpi_read_raw_from_sgl+0xf2/0x146
 [<ffffffff8132a95c>] rsa_verify+0x9d/0xee
 [<ffffffff8132acca>] ? pkcs1pad_sg_set_buf+0x2e/0xbb
 [<ffffffff8132af40>] pkcs1pad_verify+0xc0/0xe1
 [<ffffffff8133cb5e>] public_key_verify_signature+0x1b0/0x228
 [<ffffffff8133d974>] x509_check_for_self_signed+0xa1/0xc4
 [<ffffffff8133cdde>] x509_cert_parse+0x167/0x1a1
 [<ffffffff8133d609>] x509_key_preparse+0x21/0x1a1
 [<ffffffff8133c3d7>] asymmetric_key_preparse+0x34/0x61
 [<ffffffff812fc9f3>] key_create_or_update+0x145/0x399
 [<ffffffff812fe227>] SyS_add_key+0x154/0x19e
 [<ffffffff81001c2b>] do_syscall_64+0x80/0x191
 [<ffffffff816825e4>] entry_SYSCALL64_slow_path+0x25/0x25
Code: 56 41 55 41 54 53 48 81 ec a8 00 00 00 44 8b 71 04 8b 42 04 4c 8b 67 18 45 85 f6 89 45 80 0f 84 b4 06 00 00 85 c0 75 2f 41 ff ce <49> c7 04 24 01 00 00 00 b0 01 75 0b 48 8b 41 18 48 83 38 01 0f
RIP  [<ffffffff8138ce5d>] mpi_powm+0x32/0x7e6
 RSP <ffff880401297ad8>
CR2: 0000000000000000
---[ end trace d82015255d4a5d8d ]---

Basically, this is a backport of a libgcrypt patch:

	http://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git;a=patch;h=6e1adb05d290aeeb1c230c763970695f4a538526

Fixes: cdec9cb516 ("crypto: GnuPG based MPI lib - source files (part 1)")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>
cc: linux-ima-devel@lists.sourceforge.net
cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.l.morris@oracle.com>
2016-11-25 12:57:50 +11:00

329 lines
8.4 KiB
C

/* mpi-pow.c - MPI functions
* Copyright (C) 1994, 1996, 1998, 2000 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* GnuPG 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*
* Note: This code is heavily based on the GNU MP Library.
* Actually it's the same code with only minor changes in the
* way the data is stored; this is to support the abstraction
* of an optional secure memory allocation which may be used
* to avoid revealing of sensitive data due to paging etc.
* The GNU MP Library itself is published under the LGPL;
* however I decided to publish this code under the plain GPL.
*/
#include <linux/string.h>
#include "mpi-internal.h"
#include "longlong.h"
/****************
* RES = BASE ^ EXP mod MOD
*/
int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
{
mpi_ptr_t mp_marker = NULL, bp_marker = NULL, ep_marker = NULL;
mpi_ptr_t xp_marker = NULL;
mpi_ptr_t tspace = NULL;
mpi_ptr_t rp, ep, mp, bp;
mpi_size_t esize, msize, bsize, rsize;
int esign, msign, bsign, rsign;
mpi_size_t size;
int mod_shift_cnt;
int negative_result;
int assign_rp = 0;
mpi_size_t tsize = 0; /* to avoid compiler warning */
/* fixme: we should check that the warning is void */
int rc = -ENOMEM;
esize = exp->nlimbs;
msize = mod->nlimbs;
size = 2 * msize;
esign = exp->sign;
msign = mod->sign;
rp = res->d;
ep = exp->d;
if (!msize)
return -EINVAL;
if (!esize) {
/* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
* depending on if MOD equals 1. */
res->nlimbs = (msize == 1 && mod->d[0] == 1) ? 0 : 1;
if (res->nlimbs) {
if (mpi_resize(res, 1) < 0)
goto enomem;
rp = res->d;
rp[0] = 1;
}
res->sign = 0;
goto leave;
}
/* Normalize MOD (i.e. make its most significant bit set) as required by
* mpn_divrem. This will make the intermediate values in the calculation
* slightly larger, but the correct result is obtained after a final
* reduction using the original MOD value. */
mp = mp_marker = mpi_alloc_limb_space(msize);
if (!mp)
goto enomem;
mod_shift_cnt = count_leading_zeros(mod->d[msize - 1]);
if (mod_shift_cnt)
mpihelp_lshift(mp, mod->d, msize, mod_shift_cnt);
else
MPN_COPY(mp, mod->d, msize);
bsize = base->nlimbs;
bsign = base->sign;
if (bsize > msize) { /* The base is larger than the module. Reduce it. */
/* Allocate (BSIZE + 1) with space for remainder and quotient.
* (The quotient is (bsize - msize + 1) limbs.) */
bp = bp_marker = mpi_alloc_limb_space(bsize + 1);
if (!bp)
goto enomem;
MPN_COPY(bp, base->d, bsize);
/* We don't care about the quotient, store it above the remainder,
* at BP + MSIZE. */
mpihelp_divrem(bp + msize, 0, bp, bsize, mp, msize);
bsize = msize;
/* Canonicalize the base, since we are going to multiply with it
* quite a few times. */
MPN_NORMALIZE(bp, bsize);
} else
bp = base->d;
if (!bsize) {
res->nlimbs = 0;
res->sign = 0;
goto leave;
}
if (res->alloced < size) {
/* We have to allocate more space for RES. If any of the input
* parameters are identical to RES, defer deallocation of the old
* space. */
if (rp == ep || rp == mp || rp == bp) {
rp = mpi_alloc_limb_space(size);
if (!rp)
goto enomem;
assign_rp = 1;
} else {
if (mpi_resize(res, size) < 0)
goto enomem;
rp = res->d;
}
} else { /* Make BASE, EXP and MOD not overlap with RES. */
if (rp == bp) {
/* RES and BASE are identical. Allocate temp. space for BASE. */
BUG_ON(bp_marker);
bp = bp_marker = mpi_alloc_limb_space(bsize);
if (!bp)
goto enomem;
MPN_COPY(bp, rp, bsize);
}
if (rp == ep) {
/* RES and EXP are identical. Allocate temp. space for EXP. */
ep = ep_marker = mpi_alloc_limb_space(esize);
if (!ep)
goto enomem;
MPN_COPY(ep, rp, esize);
}
if (rp == mp) {
/* RES and MOD are identical. Allocate temporary space for MOD. */
BUG_ON(mp_marker);
mp = mp_marker = mpi_alloc_limb_space(msize);
if (!mp)
goto enomem;
MPN_COPY(mp, rp, msize);
}
}
MPN_COPY(rp, bp, bsize);
rsize = bsize;
rsign = bsign;
{
mpi_size_t i;
mpi_ptr_t xp;
int c;
mpi_limb_t e;
mpi_limb_t carry_limb;
struct karatsuba_ctx karactx;
xp = xp_marker = mpi_alloc_limb_space(2 * (msize + 1));
if (!xp)
goto enomem;
memset(&karactx, 0, sizeof karactx);
negative_result = (ep[0] & 1) && base->sign;
i = esize - 1;
e = ep[i];
c = count_leading_zeros(e);
e = (e << c) << 1; /* shift the exp bits to the left, lose msb */
c = BITS_PER_MPI_LIMB - 1 - c;
/* Main loop.
*
* Make the result be pointed to alternately by XP and RP. This
* helps us avoid block copying, which would otherwise be necessary
* with the overlap restrictions of mpihelp_divmod. With 50% probability
* the result after this loop will be in the area originally pointed
* by RP (==RES->d), and with 50% probability in the area originally
* pointed to by XP.
*/
for (;;) {
while (c) {
mpi_ptr_t tp;
mpi_size_t xsize;
/*if (mpihelp_mul_n(xp, rp, rp, rsize) < 0) goto enomem */
if (rsize < KARATSUBA_THRESHOLD)
mpih_sqr_n_basecase(xp, rp, rsize);
else {
if (!tspace) {
tsize = 2 * rsize;
tspace =
mpi_alloc_limb_space(tsize);
if (!tspace)
goto enomem;
} else if (tsize < (2 * rsize)) {
mpi_free_limb_space(tspace);
tsize = 2 * rsize;
tspace =
mpi_alloc_limb_space(tsize);
if (!tspace)
goto enomem;
}
mpih_sqr_n(xp, rp, rsize, tspace);
}
xsize = 2 * rsize;
if (xsize > msize) {
mpihelp_divrem(xp + msize, 0, xp, xsize,
mp, msize);
xsize = msize;
}
tp = rp;
rp = xp;
xp = tp;
rsize = xsize;
if ((mpi_limb_signed_t) e < 0) {
/*mpihelp_mul( xp, rp, rsize, bp, bsize ); */
if (bsize < KARATSUBA_THRESHOLD) {
mpi_limb_t tmp;
if (mpihelp_mul
(xp, rp, rsize, bp, bsize,
&tmp) < 0)
goto enomem;
} else {
if (mpihelp_mul_karatsuba_case
(xp, rp, rsize, bp, bsize,
&karactx) < 0)
goto enomem;
}
xsize = rsize + bsize;
if (xsize > msize) {
mpihelp_divrem(xp + msize, 0,
xp, xsize, mp,
msize);
xsize = msize;
}
tp = rp;
rp = xp;
xp = tp;
rsize = xsize;
}
e <<= 1;
c--;
}
i--;
if (i < 0)
break;
e = ep[i];
c = BITS_PER_MPI_LIMB;
}
/* We shifted MOD, the modulo reduction argument, left MOD_SHIFT_CNT
* steps. Adjust the result by reducing it with the original MOD.
*
* Also make sure the result is put in RES->d (where it already
* might be, see above).
*/
if (mod_shift_cnt) {
carry_limb =
mpihelp_lshift(res->d, rp, rsize, mod_shift_cnt);
rp = res->d;
if (carry_limb) {
rp[rsize] = carry_limb;
rsize++;
}
} else {
MPN_COPY(res->d, rp, rsize);
rp = res->d;
}
if (rsize >= msize) {
mpihelp_divrem(rp + msize, 0, rp, rsize, mp, msize);
rsize = msize;
}
/* Remove any leading zero words from the result. */
if (mod_shift_cnt)
mpihelp_rshift(rp, rp, rsize, mod_shift_cnt);
MPN_NORMALIZE(rp, rsize);
mpihelp_release_karatsuba_ctx(&karactx);
}
if (negative_result && rsize) {
if (mod_shift_cnt)
mpihelp_rshift(mp, mp, msize, mod_shift_cnt);
mpihelp_sub(rp, mp, msize, rp, rsize);
rsize = msize;
rsign = msign;
MPN_NORMALIZE(rp, rsize);
}
res->nlimbs = rsize;
res->sign = rsign;
leave:
rc = 0;
enomem:
if (assign_rp)
mpi_assign_limb_space(res, rp, size);
if (mp_marker)
mpi_free_limb_space(mp_marker);
if (bp_marker)
mpi_free_limb_space(bp_marker);
if (ep_marker)
mpi_free_limb_space(ep_marker);
if (xp_marker)
mpi_free_limb_space(xp_marker);
if (tspace)
mpi_free_limb_space(tspace);
return rc;
}
EXPORT_SYMBOL_GPL(mpi_powm);