[PATCH 1/2] X.509: Fix double free in x509_cert_parse()

[PATCH 1/2] X.509: Fix double free in x509_cert_parse()

[David Howells]

From: Andrey Ryabinin <aryabinin@virtuozzo.com>

We shouldn't free cert->pub->key in x509_cert_parse() because
x509_free_certificate() also does this:
	BUG: Double free or freeing an invalid pointer
	...
	Call Trace:
	 [<ffffffff81896c20>] dump_stack+0x63/0x83
	 [<ffffffff81356571>] kasan_object_err+0x21/0x70
	 [<ffffffff81356ed9>] kasan_report_double_free+0x49/0x60
	 [<ffffffff813561ad>] kasan_slab_free+0x9d/0xc0
	 [<ffffffff81350b7a>] kfree+0x8a/0x1a0
	 [<ffffffff81844fbf>] public_key_free+0x1f/0x30
	 [<ffffffff818455d4>] x509_free_certificate+0x24/0x90
	 [<ffffffff818460bc>] x509_cert_parse+0x2bc/0x300
	 [<ffffffff81846cae>] x509_key_preparse+0x3e/0x330
	 [<ffffffff818444cf>] asymmetric_key_preparse+0x6f/0x100
	 [<ffffffff8178bec0>] key_create_or_update+0x260/0x5f0
	 [<ffffffff8178e6d9>] SyS_add_key+0x199/0x2a0
	 [<ffffffff821d823b>] entry_SYSCALL_64_fastpath+0x1e/0xad
	Object at ffff880110bd1900, in cache kmalloc-512 size: 512
	....
	Freed:
	PID = 2579
	[<ffffffff8104283b>] save_stack_trace+0x1b/0x20
	[<ffffffff813558f6>] save_stack+0x46/0xd0
	[<ffffffff81356183>] kasan_slab_free+0x73/0xc0
	[<ffffffff81350b7a>] kfree+0x8a/0x1a0
	[<ffffffff818460a3>] x509_cert_parse+0x2a3/0x300
	[<ffffffff81846cae>] x509_key_preparse+0x3e/0x330
	[<ffffffff818444cf>] asymmetric_key_preparse+0x6f/0x100
	[<ffffffff8178bec0>] key_create_or_update+0x260/0x5f0
	[<ffffffff8178e6d9>] SyS_add_key+0x199/0x2a0
	[<ffffffff821d823b>] entry_SYSCALL_64_fastpath+0x1e/0xad

Fixes: db6c43bd2132 ("crypto: KEYS: convert public key and digsig asym to the akcipher api")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
---

 crypto/asymmetric_keys/x509_cert_parser.c |    1 -
 1 file changed, 1 deletion(-)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 865f46ea724f..c80765b211cf 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -133,7 +133,6 @@ struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
 	return cert;
 
 error_decode:
-	kfree(cert->pub->key);
 	kfree(ctx);
 error_no_ctx:
 	x509_free_certificate(cert);

[PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[David Howells]

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
handling the 0-exponent case.

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 ]---

Fixes: cdec9cb5167a ('crypto: GnuPG based MPI lib - source files (part 1)')
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
---

 lib/mpi/mpi-pow.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
index 5464c8744ea9..d72d347e62d1 100644
--- a/lib/mpi/mpi-pow.c
+++ b/lib/mpi/mpi-pow.c
@@ -64,6 +64,11 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 	if (!esize) {
 		/* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
 		 * depending on if MOD equals 1.  */
+		if (!rp) {
+			if (mpi_resize(res, 1) < 0)
+				return -ENOMEM;
+			rp = res->d;
+		}
 		rp[0] = 1;
 		res->nlimbs = (msize == 1 && mod->d[0] == 1) ? 0 : 1;
 		res->sign = 0;

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> +		if (!rp) {
> +			if (mpi_resize(res, 1) < 0)

This is better done with RESIZE_IF_NEEDED().

David

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[Andrey Ryabinin]

2016-11-24 11:51 GMT+03:00 David Howells <dhowells@redhat.com>:
> 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
> handling the 0-exponent case.
>
> 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 ]---
>
> Fixes: cdec9cb5167a ('crypto: GnuPG based MPI lib - source files (part 1)')
> 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
> ---
>
>  lib/mpi/mpi-pow.c |    5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
> index 5464c8744ea9..d72d347e62d1 100644
> --- a/lib/mpi/mpi-pow.c
> +++ b/lib/mpi/mpi-pow.c
> @@ -64,6 +64,11 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
>         if (!esize) {
>                 /* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
>                  * depending on if MOD equals 1.  */
> +               if (!rp) {
> +                       if (mpi_resize(res, 1) < 0)
> +                               return -ENOMEM;
> +                       rp = res->d;
> +               }

I'm also made a fix for this yesterday -
http://lkml.kernel.org/r/1479918484-31952-1-git-send-email-aryabinin@virtuozzo.com
The only small difference is that in my the limb space is not
allocated when it's not needed, i.e. when res->nlimbs == 0.

>                 rp[0] = 1;
>                 res->nlimbs = (msize == 1 && mod->d[0] == 1) ? 0 : 1;
>                 res->sign = 0;
>

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[Andrey Ryabinin]

2016-11-24 14:17 GMT+03:00 David Howells <dhowells@redhat.com>:
> David Howells <dhowells@redhat.com> wrote:
>
>> +             if (!rp) {
>> +                     if (mpi_resize(res, 1) < 0)
>
> This is better done with RESIZE_IF_NEEDED().
>

mpi_resize() is equal to RESIZE_IF_NEEDED(), it also checks for allocated space:

int mpi_resize(MPI a, unsigned nlimbs)
{
....
   if (nlimbs <= a->alloced)
    return 0; /* no need to do it */



> David

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[David Howells]

Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:

> > David Howells <dhowells@redhat.com> wrote:
> >
> >> +             if (!rp) {
> >> +                     if (mpi_resize(res, 1) < 0)
> >
> > This is better done with RESIZE_IF_NEEDED().
> >
> 
> mpi_resize() is equal to RESIZE_IF_NEEDED(), it also checks for allocated space:
> 
> int mpi_resize(MPI a, unsigned nlimbs)
> {
> ....
>    if (nlimbs <= a->alloced)
>     return 0; /* no need to do it */

Hmmm...  In that case, should your patch use mpi_resize() rather than
RESIZE_IF_NEEDED()?  It's a trivial case that we should perhaps weed out much
earlier (ie. reject the key if exp<2 or mod<2), but it would make the object
file slightly smaller not to do the test twice.

David

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[David Howells]

Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:

> I'm also made a fix for this yesterday -
> http://lkml.kernel.org/r/1479918484-31952-1-git-send-email-aryabinin@virtuozzo.com

I should add a record to the MAINTAINERS file that directs patches to MPI to
keyrings@vger.kernel.org so that I see things like this.

> The only small difference is that in my the limb space is not
> allocated when it's not needed, i.e. when res->nlimbs == 0.

I guess if nlimbs is 0 then the value is 0, right?

David

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[Andrey Ryabinin]

2016-11-24 14:33 GMT+03:00 David Howells <dhowells@redhat.com>:
> Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
>
>> > David Howells <dhowells@redhat.com> wrote:
>> >
>> >> +             if (!rp) {
>> >> +                     if (mpi_resize(res, 1) < 0)
>> >
>> > This is better done with RESIZE_IF_NEEDED().
>> >
>>
>> mpi_resize() is equal to RESIZE_IF_NEEDED(), it also checks for allocated space:
>>
>> int mpi_resize(MPI a, unsigned nlimbs)
>> {
>> ....
>>    if (nlimbs <= a->alloced)
>>     return 0; /* no need to do it */
>
> Hmmm...  In that case, should your patch use mpi_resize() rather than
> RESIZE_IF_NEEDED()? It's a trivial case that we should perhaps weed out much
> earlier (ie. reject the key if exp<2 or mod<2), but it would make the object
> file slightly smaller not to do the test twice.
>

Right, it could be mpi_resize(). I realized that these two functions
do the exactly the same thing only after I send the patch.
We could even remove RESIZE_IF_NEEDED() to not confuse people, because
currently it has no users.

> David

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[Andrey Ryabinin]

2016-11-24 14:35 GMT+03:00 David Howells <dhowells@redhat.com>:
> Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
>
>> I'm also made a fix for this yesterday -
>> http://lkml.kernel.org/r/1479918484-31952-1-git-send-email-aryabinin@virtuozzo.com
>
> I should add a record to the MAINTAINERS file that directs patches to MPI to
> keyrings@vger.kernel.org so that I see things like this.
>

Would be nice. It was unclear who maintains it. Since all recent
changes to mpi were merged through crypto tree,
I send this to crypto maintainers.

>> The only small difference is that in my the limb space is not
>> allocated when it's not needed, i.e. when res->nlimbs == 0.
>
> I guess if nlimbs is 0 then the value is 0, right?
>

Right, as far as I understand.


> David

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[David Howells]

I've integrated my patch and yours (see attached) - are you okay with the
result?

> We could even remove RESIZE_IF_NEEDED() to not confuse people, because
> currently it has no users.

Yep, but that'll have to be a separate patch.

David
---
commit cfe384ff418f11db2a3647f79635393ecb723c6f
Author: Andrey Ryabinin <aryabinin@virtuozzo.com>
Date:   Wed Nov 23 16:44:47 2016 +0000

    mpi: Fix NULL ptr dereference in mpi_powm()
    
    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: cdec9cb5167a ("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

diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
index 5464c8744ea9..94c30138bd32 100644
--- a/lib/mpi/mpi-pow.c
+++ b/lib/mpi/mpi-pow.c
@@ -64,6 +64,9 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 	if (!esize) {
 		/* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
 		 * depending on if MOD equals 1.  */
+		if (RESIZE_IF_NEEDED(res, 1) < 0)
+			return -ENOMEM;
+		rp = res->d;
 		rp[0] = 1;
 		res->nlimbs = (msize == 1 && mod->d[0] == 1) ? 0 : 1;
 		res->sign = 0;

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> I've integrated my patch and yours (see attached) - are you okay with the
> result?

It helps if I commit the changes...

David
---
commit 1dc938c3393d8ff0e04723956ed00ec21e2b2a89
Author: Andrey Ryabinin <aryabinin@virtuozzo.com>
Date:   Wed Nov 23 16:44:47 2016 +0000

    mpi: Fix NULL ptr dereference in mpi_powm()
    
    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: cdec9cb5167a ("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

diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
index 5464c8744ea9..e24388a863a7 100644
--- a/lib/mpi/mpi-pow.c
+++ b/lib/mpi/mpi-pow.c
@@ -64,8 +64,13 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 	if (!esize) {
 		/* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
 		 * depending on if MOD equals 1.  */
-		rp[0] = 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;
 	}

Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

[Andrey Ryabinin]

On 11/24/2016 03:57 PM, David Howells wrote:
> David Howells <dhowells@redhat.com> wrote:
> 
>> I've integrated my patch and yours (see attached) - are you okay with the
>> result?
> 
> It helps if I commit the changes...
> 

Looks good, thanks.

> David
> ---
> commit 1dc938c3393d8ff0e04723956ed00ec21e2b2a89
> Author: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Date:   Wed Nov 23 16:44:47 2016 +0000
> 
>     mpi: Fix NULL ptr dereference in mpi_powm()
>     
>     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: cdec9cb5167a ("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
> 
> diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
> index 5464c8744ea9..e24388a863a7 100644
> --- a/lib/mpi/mpi-pow.c
> +++ b/lib/mpi/mpi-pow.c
> @@ -64,8 +64,13 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
>  	if (!esize) {
>  		/* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
>  		 * depending on if MOD equals 1.  */
> -		rp[0] = 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;
>  	}
>