[PATCH 0/2] net: socket: Fix potential spectre v1 gadgets

[PATCH 0/2] net: socket: Fix potential spectre v1 gadgets

[Jeremy Cline]

Hi folks,

This fixes a pair of potential spectre v1 gadgets.

Note that because the speculation window is large, the policy is to stop
the speculative out-of-bounds load and not worry if the attack can be
completed with a dependent load or store[0].

[0] https://marc.info/?l=linux-kernel&m=152449131114778

Jeremy Cline (2):
  net: socket: fix potential spectre v1 gadget in socketcall
  net: socket: Fix potential spectre v1 gadget in sock_is_registered

 net/socket.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

-- 
2.17.1

[PATCH 1/2] net: socket: fix potential spectre v1 gadget in socketcall

[Jeremy Cline]

'call' is a user-controlled value, so sanitize the array index after the
bounds check to avoid speculating past the bounds of the 'nargs' array.

Found with the help of Smatch:

net/socket.c:2508 __do_sys_socketcall() warn: potential spectre issue
'nargs' [r] (local cap)

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---
 net/socket.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/socket.c b/net/socket.c
index 3015ddace71e..f15d5cbb3ba4 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -89,6 +89,7 @@
 #include <linux/magic.h>
 #include <linux/slab.h>
 #include <linux/xattr.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -2504,6 +2505,7 @@ SYSCALL_DEFINE2(socketcall, int, call, unsigned long __user *, args)
 
 	if (call < 1 || call > SYS_SENDMMSG)
 		return -EINVAL;
+	call = array_index_nospec(call, SYS_SENDMMSG + 1);
 
 	len = nargs[call];
 	if (len > sizeof(a))
-- 
2.17.1

[PATCH 2/2] net: socket: Fix potential spectre v1 gadget in sock_is_registered

[Jeremy Cline]

'family' can be a user-controlled value, so sanitize it after the bounds
check to avoid speculative out-of-bounds access.

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---
 net/socket.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/socket.c b/net/socket.c
index f15d5cbb3ba4..608e29ae6baf 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2672,7 +2672,8 @@ EXPORT_SYMBOL(sock_unregister);
 
 bool sock_is_registered(int family)
 {
-	return family < NPROTO && rcu_access_pointer(net_families[family]);
+	return family < NPROTO &&
+		rcu_access_pointer(net_families[array_index_nospec(family, NPROTO)]);
 }
 
 static int __init sock_init(void)
-- 
2.17.1

Re: [PATCH 0/2] net: socket: Fix potential spectre v1 gadgets

[David Miller]

From: Jeremy Cline <jcline@redhat.com>
Date: Fri, 27 Jul 2018 22:43:00 +0000

> This fixes a pair of potential spectre v1 gadgets.
> 
> Note that because the speculation window is large, the policy is to stop
> the speculative out-of-bounds load and not worry if the attack can be
> completed with a dependent load or store[0].
> 
> [0] https://marc.info/?l=linux-kernel&m=152449131114778

Series applied, thank you.

Re: [PATCH 2/2] net: socket: Fix potential spectre v1 gadget in sock_is_registered

[Josh Poimboeuf]

On Fri, Jul 27, 2018 at 10:43:02PM +0000, Jeremy Cline wrote:
> 'family' can be a user-controlled value, so sanitize it after the bounds
> check to avoid speculative out-of-bounds access.
> 
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Jeremy Cline <jcline@redhat.com>
> ---
>  net/socket.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/socket.c b/net/socket.c
> index f15d5cbb3ba4..608e29ae6baf 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2672,7 +2672,8 @@ EXPORT_SYMBOL(sock_unregister);
>  
>  bool sock_is_registered(int family)
>  {
> -	return family < NPROTO && rcu_access_pointer(net_families[family]);
> +	return family < NPROTO &&
> +		rcu_access_pointer(net_families[array_index_nospec(family, NPROTO)]);
>  }
>  
>  static int __init sock_init(void)

This is another one where I think it would be better to do the nospec
clamp higher up the call chain.  The untrusted 'family' value comes from
__sock_diag_cmd():

__sock_diag_cmd
  sock_load_diag_module
    sock_is_registered

That function has a bounds check, and also uses the value in some other
array accesses:

	if (req->sdiag_family >= AF_MAX)
		return -EINVAL;

	if (sock_diag_handlers[req->sdiag_family] == NULL)
		sock_load_diag_module(req->sdiag_family, 0);

	mutex_lock(&sock_diag_table_mutex);
	hndl = sock_diag_handlers[req->sdiag_family];
	...

So I think clamping 'req->sdiag_family' right after the bounds check
would be the way to go.

-- 
Josh

Re: [PATCH 1/2] net: socket: fix potential spectre v1 gadget in socketcall

[Josh Poimboeuf]

On Fri, Jul 27, 2018 at 10:43:01PM +0000, Jeremy Cline wrote:
> 'call' is a user-controlled value, so sanitize the array index after the
> bounds check to avoid speculating past the bounds of the 'nargs' array.
> 
> Found with the help of Smatch:
> 
> net/socket.c:2508 __do_sys_socketcall() warn: potential spectre issue
> 'nargs' [r] (local cap)
> 
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Jeremy Cline <jcline@redhat.com>
> ---
>  net/socket.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/socket.c b/net/socket.c
> index 3015ddace71e..f15d5cbb3ba4 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -89,6 +89,7 @@
>  #include <linux/magic.h>
>  #include <linux/slab.h>
>  #include <linux/xattr.h>
> +#include <linux/nospec.h>
>  
>  #include <linux/uaccess.h>
>  #include <asm/unistd.h>
> @@ -2504,6 +2505,7 @@ SYSCALL_DEFINE2(socketcall, int, call, unsigned long __user *, args)
>  
>  	if (call < 1 || call > SYS_SENDMMSG)
>  		return -EINVAL;
> +	call = array_index_nospec(call, SYS_SENDMMSG + 1);
>  
>  	len = nargs[call];
>  	if (len > sizeof(a))

Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>

-- 
Josh

Re: [PATCH 2/2] net: socket: Fix potential spectre v1 gadget in sock_is_registered

[Jeremy Cline]

On 07/29/2018 09:59 AM, Josh Poimboeuf wrote:
> On Fri, Jul 27, 2018 at 10:43:02PM +0000, Jeremy Cline wrote:
>> 'family' can be a user-controlled value, so sanitize it after the bounds
>> check to avoid speculative out-of-bounds access.
>>
>> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Jeremy Cline <jcline@redhat.com>
>> ---
>>  net/socket.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/socket.c b/net/socket.c
>> index f15d5cbb3ba4..608e29ae6baf 100644
>> --- a/net/socket.c
>> +++ b/net/socket.c
>> @@ -2672,7 +2672,8 @@ EXPORT_SYMBOL(sock_unregister);
>>  
>>  bool sock_is_registered(int family)
>>  {
>> -	return family < NPROTO && rcu_access_pointer(net_families[family]);
>> +	return family < NPROTO &&
>> +		rcu_access_pointer(net_families[array_index_nospec(family, NPROTO)]);
>>  }
>>  
>>  static int __init sock_init(void)
> 
> This is another one where I think it would be better to do the nospec
> clamp higher up the call chain.  The untrusted 'family' value comes from
> __sock_diag_cmd():
> 
> __sock_diag_cmd
>   sock_load_diag_module
>     sock_is_registered
> 
> That function has a bounds check, and also uses the value in some other
> array accesses:
> 
> 	if (req->sdiag_family >= AF_MAX)
> 		return -EINVAL;
> 
> 	if (sock_diag_handlers[req->sdiag_family] == NULL)
> 		sock_load_diag_module(req->sdiag_family, 0);
> 
> 	mutex_lock(&sock_diag_table_mutex);
> 	hndl = sock_diag_handlers[req->sdiag_family];
> 	...
> 
> So I think clamping 'req->sdiag_family' right after the bounds check
> would be the way to go.
> 

Indeed, the clamp there would cover this clamp. I had a scheme that I
quickly fix all the gadgets in functions with local comparisons, but
clearly that's going to result in call chains with multiple clamps.

I can fix this in a follow-up with a clamp here, or respin this patch
set, whatever is easier for David.

Thanks for the review!

Re: [PATCH 2/2] net: socket: Fix potential spectre v1 gadget in sock_is_registered

[Josh Poimboeuf]

On Sun, Jul 29, 2018 at 11:59:36AM -0400, Jeremy Cline wrote:
> On 07/29/2018 09:59 AM, Josh Poimboeuf wrote:
> > On Fri, Jul 27, 2018 at 10:43:02PM +0000, Jeremy Cline wrote:
> >> 'family' can be a user-controlled value, so sanitize it after the bounds
> >> check to avoid speculative out-of-bounds access.
> >>
> >> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> >> Cc: stable@vger.kernel.org
> >> Signed-off-by: Jeremy Cline <jcline@redhat.com>
> >> ---
> >>  net/socket.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/net/socket.c b/net/socket.c
> >> index f15d5cbb3ba4..608e29ae6baf 100644
> >> --- a/net/socket.c
> >> +++ b/net/socket.c
> >> @@ -2672,7 +2672,8 @@ EXPORT_SYMBOL(sock_unregister);
> >>  
> >>  bool sock_is_registered(int family)
> >>  {
> >> -	return family < NPROTO && rcu_access_pointer(net_families[family]);
> >> +	return family < NPROTO &&
> >> +		rcu_access_pointer(net_families[array_index_nospec(family, NPROTO)]);
> >>  }
> >>  
> >>  static int __init sock_init(void)
> > 
> > This is another one where I think it would be better to do the nospec
> > clamp higher up the call chain.  The untrusted 'family' value comes from
> > __sock_diag_cmd():
> > 
> > __sock_diag_cmd
> >   sock_load_diag_module
> >     sock_is_registered
> > 
> > That function has a bounds check, and also uses the value in some other
> > array accesses:
> > 
> > 	if (req->sdiag_family >= AF_MAX)
> > 		return -EINVAL;
> > 
> > 	if (sock_diag_handlers[req->sdiag_family] == NULL)
> > 		sock_load_diag_module(req->sdiag_family, 0);
> > 
> > 	mutex_lock(&sock_diag_table_mutex);
> > 	hndl = sock_diag_handlers[req->sdiag_family];
> > 	...
> > 
> > So I think clamping 'req->sdiag_family' right after the bounds check
> > would be the way to go.
> > 
> 
> Indeed, the clamp there would cover this clamp. I had a scheme that I
> quickly fix all the gadgets in functions with local comparisons, but
> clearly that's going to result in call chains with multiple clamps.
> 
> I can fix this in a follow-up with a clamp here, or respin this patch
> set, whatever is easier for David.

Hi Jeremy,

Just checking up on this... since this patch was merged, will you be
doing a followup patch?

-- 
Josh

Re: [PATCH 2/2] net: socket: Fix potential spectre v1 gadget in sock_is_registered

[Jeremy Cline]

On 08/13/2018 06:16 PM, Josh Poimboeuf wrote:
> On Sun, Jul 29, 2018 at 11:59:36AM -0400, Jeremy Cline wrote:
>> On 07/29/2018 09:59 AM, Josh Poimboeuf wrote:
>>> On Fri, Jul 27, 2018 at 10:43:02PM +0000, Jeremy Cline wrote:
>>>> 'family' can be a user-controlled value, so sanitize it after the bounds
>>>> check to avoid speculative out-of-bounds access.
>>>>
>>>> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
>>>> Cc: stable@vger.kernel.org
>>>> Signed-off-by: Jeremy Cline <jcline@redhat.com>
>>>> ---
>>>>  net/socket.c | 3 ++-
>>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/socket.c b/net/socket.c
>>>> index f15d5cbb3ba4..608e29ae6baf 100644
>>>> --- a/net/socket.c
>>>> +++ b/net/socket.c
>>>> @@ -2672,7 +2672,8 @@ EXPORT_SYMBOL(sock_unregister);
>>>>  
>>>>  bool sock_is_registered(int family)
>>>>  {
>>>> -	return family < NPROTO && rcu_access_pointer(net_families[family]);
>>>> +	return family < NPROTO &&
>>>> +		rcu_access_pointer(net_families[array_index_nospec(family, NPROTO)]);
>>>>  }
>>>>  
>>>>  static int __init sock_init(void)
>>>
>>> This is another one where I think it would be better to do the nospec
>>> clamp higher up the call chain.  The untrusted 'family' value comes from
>>> __sock_diag_cmd():
>>>
>>> __sock_diag_cmd
>>>   sock_load_diag_module
>>>     sock_is_registered
>>>
>>> That function has a bounds check, and also uses the value in some other
>>> array accesses:
>>>
>>> 	if (req->sdiag_family >= AF_MAX)
>>> 		return -EINVAL;
>>>
>>> 	if (sock_diag_handlers[req->sdiag_family] == NULL)
>>> 		sock_load_diag_module(req->sdiag_family, 0);
>>>
>>> 	mutex_lock(&sock_diag_table_mutex);
>>> 	hndl = sock_diag_handlers[req->sdiag_family];
>>> 	...
>>>
>>> So I think clamping 'req->sdiag_family' right after the bounds check
>>> would be the way to go.
>>>
>>
>> Indeed, the clamp there would cover this clamp. I had a scheme that I
>> quickly fix all the gadgets in functions with local comparisons, but
>> clearly that's going to result in call chains with multiple clamps.
>>
>> I can fix this in a follow-up with a clamp here, or respin this patch
>> set, whatever is easier for David.
> 
> Hi Jeremy,
> 
> Just checking up on this... since this patch was merged, will you be
> doing a followup patch?
> 

Yes, apologies, I've been traveling. I'll have a patch tomorrow.