[PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[David Ahern]

Andrey reported a fault in the IPv6 route code:

kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 1 PID: 4035 Comm: a.out Not tainted 4.11.0-rc7+ #250
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff880069809600 task.stack: ffff880062dc8000
RIP: 0010:ip6_rt_cache_alloc+0xa6/0x560 net/ipv6/route.c:975
RSP: 0018:ffff880062dced30 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffff8800670561c0 RCX: 0000000000000006
RDX: 0000000000000003 RSI: ffff880062dcfb28 RDI: 0000000000000018
RBP: ffff880062dced68 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff880062dcfb28 R14: dffffc0000000000 R15: 0000000000000000
FS:  00007feebe37e7c0(0000) GS:ffff88006cb00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000205a0fe4 CR3: 000000006b5c9000 CR4: 00000000000006e0
Call Trace:
 ip6_pol_route+0x1512/0x1f20 net/ipv6/route.c:1128
 ip6_pol_route_output+0x4c/0x60 net/ipv6/route.c:1212
...

Andrey's syzkaller program passes rtmsg.rtmsg_flags with the RTF_PCPU bit
set. Flags passed to the kernel are blindly copied to the allocated
rt6_info by ip6_route_info_create making a newly inserted route appear
as though it is a per-cpu route. ip6_rt_cache_alloc sees the flag set
and expects rt->dst.from to be set - which it is not since it is not
really a per-cpu copy. The subsequent call to __ip6_dst_alloc then
generates the fault.

Fix by checking for the flag and failing with EINVAL.

Fixes: d52d3997f843f ("ipv6: Create percpu rt6_info")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
---
 include/uapi/linux/ipv6_route.h | 2 +-
 net/ipv6/route.c                | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/ipv6_route.h b/include/uapi/linux/ipv6_route.h
index 85bbb1799df3..d496c02e14bc 100644
--- a/include/uapi/linux/ipv6_route.h
+++ b/include/uapi/linux/ipv6_route.h
@@ -35,7 +35,7 @@
 #define RTF_PREF(pref)	((pref) << 27)
 #define RTF_PREF_MASK	0x18000000
 
-#define RTF_PCPU	0x40000000
+#define RTF_PCPU	0x40000000	/* read-only: can not be set by user */
 #define RTF_LOCAL	0x80000000
 
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 4ba7c49872ff..a1bf426c959b 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1854,6 +1854,10 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg)
 	int addr_type;
 	int err = -EINVAL;
 
+	/* RTF_PCPU is an internal flag; can not be set by userspace */
+	if (cfg->fc_flags & RTF_PCPU)
+		goto out;
+
 	if (cfg->fc_dst_len > 128 || cfg->fc_src_len > 128)
 		goto out;
 #ifndef CONFIG_IPV6_SUBTREES
-- 
2.9.3

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[Martin KaFai Lau]

On Wed, Apr 19, 2017 at 02:19:43PM -0700, David Ahern wrote:
> Andrey reported a fault in the IPv6 route code:
>
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 1 PID: 4035 Comm: a.out Not tainted 4.11.0-rc7+ #250
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff880069809600 task.stack: ffff880062dc8000
> RIP: 0010:ip6_rt_cache_alloc+0xa6/0x560 net/ipv6/route.c:975
> RSP: 0018:ffff880062dced30 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: ffff8800670561c0 RCX: 0000000000000006
> RDX: 0000000000000003 RSI: ffff880062dcfb28 RDI: 0000000000000018
> RBP: ffff880062dced68 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffff880062dcfb28 R14: dffffc0000000000 R15: 0000000000000000
> FS:  00007feebe37e7c0(0000) GS:ffff88006cb00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000205a0fe4 CR3: 000000006b5c9000 CR4: 00000000000006e0
> Call Trace:
>  ip6_pol_route+0x1512/0x1f20 net/ipv6/route.c:1128
>  ip6_pol_route_output+0x4c/0x60 net/ipv6/route.c:1212
> ...
>
> Andrey's syzkaller program passes rtmsg.rtmsg_flags with the RTF_PCPU bit
> set. Flags passed to the kernel are blindly copied to the allocated
> rt6_info by ip6_route_info_create making a newly inserted route appear
> as though it is a per-cpu route. ip6_rt_cache_alloc sees the flag set
> and expects rt->dst.from to be set - which it is not since it is not
> really a per-cpu copy. The subsequent call to __ip6_dst_alloc then
> generates the fault.
>
> Fix by checking for the flag and failing with EINVAL.
Thanks for the fix.

Acked-by: Martin KaFai Lau <kafai@fb.com>

>
> Fixes: d52d3997f843f ("ipv6: Create percpu rt6_info")
> Reported-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
> ---
>  include/uapi/linux/ipv6_route.h | 2 +-
>  net/ipv6/route.c                | 4 ++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/ipv6_route.h b/include/uapi/linux/ipv6_route.h
> index 85bbb1799df3..d496c02e14bc 100644
> --- a/include/uapi/linux/ipv6_route.h
> +++ b/include/uapi/linux/ipv6_route.h
> @@ -35,7 +35,7 @@
>  #define RTF_PREF(pref)	((pref) << 27)
>  #define RTF_PREF_MASK	0x18000000
>
> -#define RTF_PCPU	0x40000000
> +#define RTF_PCPU	0x40000000	/* read-only: can not be set by user */
>  #define RTF_LOCAL	0x80000000
>
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 4ba7c49872ff..a1bf426c959b 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -1854,6 +1854,10 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg)
>  	int addr_type;
>  	int err = -EINVAL;
>
> +	/* RTF_PCPU is an internal flag; can not be set by userspace */
> +	if (cfg->fc_flags & RTF_PCPU)
> +		goto out;
> +
>  	if (cfg->fc_dst_len > 128 || cfg->fc_src_len > 128)
>  		goto out;
>  #ifndef CONFIG_IPV6_SUBTREES
> --
> 2.9.3
>

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[Andrey Konovalov]

Thanks!

Tested-by: Andrey Konovalov <andreyknvl@google.com>

On Wed, Apr 19, 2017 at 11:52 PM, Martin KaFai Lau <kafai@fb.com> wrote:
> On Wed, Apr 19, 2017 at 02:19:43PM -0700, David Ahern wrote:
>> Andrey reported a fault in the IPv6 route code:
>>
>> kasan: GPF could be caused by NULL-ptr deref or user memory access
>> general protection fault: 0000 [#1] SMP KASAN
>> Modules linked in:
>> CPU: 1 PID: 4035 Comm: a.out Not tainted 4.11.0-rc7+ #250
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> task: ffff880069809600 task.stack: ffff880062dc8000
>> RIP: 0010:ip6_rt_cache_alloc+0xa6/0x560 net/ipv6/route.c:975
>> RSP: 0018:ffff880062dced30 EFLAGS: 00010206
>> RAX: dffffc0000000000 RBX: ffff8800670561c0 RCX: 0000000000000006
>> RDX: 0000000000000003 RSI: ffff880062dcfb28 RDI: 0000000000000018
>> RBP: ffff880062dced68 R08: 0000000000000001 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>> R13: ffff880062dcfb28 R14: dffffc0000000000 R15: 0000000000000000
>> FS:  00007feebe37e7c0(0000) GS:ffff88006cb00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000205a0fe4 CR3: 000000006b5c9000 CR4: 00000000000006e0
>> Call Trace:
>>  ip6_pol_route+0x1512/0x1f20 net/ipv6/route.c:1128
>>  ip6_pol_route_output+0x4c/0x60 net/ipv6/route.c:1212
>> ...
>>
>> Andrey's syzkaller program passes rtmsg.rtmsg_flags with the RTF_PCPU bit
>> set. Flags passed to the kernel are blindly copied to the allocated
>> rt6_info by ip6_route_info_create making a newly inserted route appear
>> as though it is a per-cpu route. ip6_rt_cache_alloc sees the flag set
>> and expects rt->dst.from to be set - which it is not since it is not
>> really a per-cpu copy. The subsequent call to __ip6_dst_alloc then
>> generates the fault.
>>
>> Fix by checking for the flag and failing with EINVAL.
> Thanks for the fix.
>
> Acked-by: Martin KaFai Lau <kafai@fb.com>
>
>>
>> Fixes: d52d3997f843f ("ipv6: Create percpu rt6_info")
>> Reported-by: Andrey Konovalov <andreyknvl@google.com>
>> Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
>> ---
>>  include/uapi/linux/ipv6_route.h | 2 +-
>>  net/ipv6/route.c                | 4 ++++
>>  2 files changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/uapi/linux/ipv6_route.h b/include/uapi/linux/ipv6_route.h
>> index 85bbb1799df3..d496c02e14bc 100644
>> --- a/include/uapi/linux/ipv6_route.h
>> +++ b/include/uapi/linux/ipv6_route.h
>> @@ -35,7 +35,7 @@
>>  #define RTF_PREF(pref)       ((pref) << 27)
>>  #define RTF_PREF_MASK        0x18000000
>>
>> -#define RTF_PCPU     0x40000000
>> +#define RTF_PCPU     0x40000000      /* read-only: can not be set by user */
>>  #define RTF_LOCAL    0x80000000
>>
>>
>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>> index 4ba7c49872ff..a1bf426c959b 100644
>> --- a/net/ipv6/route.c
>> +++ b/net/ipv6/route.c
>> @@ -1854,6 +1854,10 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg)
>>       int addr_type;
>>       int err = -EINVAL;
>>
>> +     /* RTF_PCPU is an internal flag; can not be set by userspace */
>> +     if (cfg->fc_flags & RTF_PCPU)
>> +             goto out;
>> +
>>       if (cfg->fc_dst_len > 128 || cfg->fc_src_len > 128)
>>               goto out;
>>  #ifndef CONFIG_IPV6_SUBTREES
>> --
>> 2.9.3
>>

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[Cong Wang]

On Wed, Apr 19, 2017 at 2:19 PM, David Ahern <dsa@cumulusnetworks.com> wrote:
>
> Fix by checking for the flag and failing with EINVAL.
>

I am still not sure about this. There are a few unused bits in
this flag, we simply ignore the rest, right? Why should we
reject this one instead of all of those we don't use?

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[David Ahern]

On 4/20/17 4:39 PM, Cong Wang wrote:
> On Wed, Apr 19, 2017 at 2:19 PM, David Ahern <dsa@cumulusnetworks.com> wrote:
>>
>> Fix by checking for the flag and failing with EINVAL.
>>
> 
> I am still not sure about this. There are a few unused bits in
> this flag, we simply ignore the rest, right? Why should we
> reject this one instead of all of those we don't use?
> 

RTF_PCPU most definitely should not be set by userspace. arguably it
should not be returned to userspace either, but it is part of the uapi.


I scanned the others. It is not clear that others should fail with
EINVAL. Certainly a mask of unused flags can be added, but to me that is
on top of this bug fix.

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[Cong Wang]

On Thu, Apr 20, 2017 at 3:43 PM, David Ahern <dsa@cumulusnetworks.com> wrote:
>
> I scanned the others. It is not clear that others should fail with
> EINVAL. Certainly a mask of unused flags can be added, but to me that is
> on top of this bug fix.
>

If we want to preserve those unused bits, we should reject them too.

RTF_PCPU is special here, it is used but only internally, so it makes
sense to silently clear it since we don't care whether people set it to
1 or 0. We should clear it for dumping too since it is internal only.

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[Martin KaFai Lau]

On Thu, Apr 20, 2017 at 04:43:03PM -0600, David Ahern wrote:
> On 4/20/17 4:39 PM, Cong Wang wrote:
> > On Wed, Apr 19, 2017 at 2:19 PM, David Ahern <dsa@cumulusnetworks.com> wrote:
> >>
> >> Fix by checking for the flag and failing with EINVAL.
> >>
> >
> > I am still not sure about this. There are a few unused bits in
> > this flag, we simply ignore the rest, right? Why should we
> > reject this one instead of all of those we don't use?
> >
>
> RTF_PCPU most definitely should not be set by userspace.
+1

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[Martin KaFai Lau]

On Thu, Apr 20, 2017 at 04:37:18PM -0700, Cong Wang wrote:
> On Thu, Apr 20, 2017 at 3:43 PM, David Ahern <dsa@cumulusnetworks.com> wrote:
> >
> > I scanned the others. It is not clear that others should fail with
> > EINVAL. Certainly a mask of unused flags can be added, but to me that is
> > on top of this bug fix.
> >
>
> If we want to preserve those unused bits, we should reject them too.
>
> RTF_PCPU is special here, it is used but only internally, so it makes
> sense to silently clear it since we don't care whether people set it to
> 1 or 0. We should clear it for dumping too since it is internal only.
I agree with DavidA. The existing bits (including RTF_PCPU) during dumping
is part of the uapi already.  We cannot stop displaying them now.

Silently accepting something instead of telling the userspace program
has a bug seems to be a dis-service to the end-user.

If there are other bits should be rejected too, they can be
done in the follow up patches.

Re: [PATCH net] net: ipv6: RTF_PCPU should not be settable from userspace

[David Miller]

From: David Ahern <dsa@cumulusnetworks.com>
Date: Wed, 19 Apr 2017 14:19:43 -0700

> Andrey reported a fault in the IPv6 route code:
> 
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 1 PID: 4035 Comm: a.out Not tainted 4.11.0-rc7+ #250
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff880069809600 task.stack: ffff880062dc8000
> RIP: 0010:ip6_rt_cache_alloc+0xa6/0x560 net/ipv6/route.c:975
> RSP: 0018:ffff880062dced30 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: ffff8800670561c0 RCX: 0000000000000006
> RDX: 0000000000000003 RSI: ffff880062dcfb28 RDI: 0000000000000018
> RBP: ffff880062dced68 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffff880062dcfb28 R14: dffffc0000000000 R15: 0000000000000000
> FS:  00007feebe37e7c0(0000) GS:ffff88006cb00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000205a0fe4 CR3: 000000006b5c9000 CR4: 00000000000006e0
> Call Trace:
>  ip6_pol_route+0x1512/0x1f20 net/ipv6/route.c:1128
>  ip6_pol_route_output+0x4c/0x60 net/ipv6/route.c:1212
> ...
> 
> Andrey's syzkaller program passes rtmsg.rtmsg_flags with the RTF_PCPU bit
> set. Flags passed to the kernel are blindly copied to the allocated
> rt6_info by ip6_route_info_create making a newly inserted route appear
> as though it is a per-cpu route. ip6_rt_cache_alloc sees the flag set
> and expects rt->dst.from to be set - which it is not since it is not
> really a per-cpu copy. The subsequent call to __ip6_dst_alloc then
> generates the fault.
> 
> Fix by checking for the flag and failing with EINVAL.
> 
> Fixes: d52d3997f843f ("ipv6: Create percpu rt6_info")
> Reported-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: David Ahern <dsa@cumulusnetworks.com>

Applied and queued up for -stable.