[PATCH net] ipv6: don't let tb6_root node share routes with other node

[PATCH net] ipv6: don't let tb6_root node share routes with other node

[Wei Wang]

From: Wei Wang <weiwan@google.com>

After commit 4512c43eac7e, if we add a route to the subtree of tb6_root
which does not have any route attached to it yet, the current code will
let tb6_root and the node in the subtree share the same route.
This could cause problem cause tb6_root has RTN_INFO flag marked and the
tree repair and clean up code will not work properly.
This commit makes sure tb6_root->leaf points back to null_entry instead
of sharing route with other node.

It fixes the following syzkaller reported issue:
BUG: KASAN: use-after-free in ipv6_prefix_equal include/net/ipv6.h:540 [inline]
BUG: KASAN: use-after-free in fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
Read of size 8 at addr ffff8801bc043498 by task syz-executor5/19819

CPU: 1 PID: 19819 Comm: syz-executor5 Not tainted 4.15.0-rc7+ #186
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 ipv6_prefix_equal include/net/ipv6.h:540 [inline]
 fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
 fib6_add+0x5fa/0x1540 net/ipv6/ip6_fib.c:1214
 __ip6_ins_rt+0x6c/0x90 net/ipv6/route.c:1003
 ip6_route_add+0x141/0x190 net/ipv6/route.c:2790
 ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
 inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
 sock_do_ioctl+0x65/0xb0 net/socket.c:958
 sock_ioctl+0x2c2/0x440 net/socket.c:1055
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452ac9
RSP: 002b:00007fd42b321c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
RDX: 0000000020fd7000 RSI: 000000000000890b RDI: 0000000000000013
RBP: 000000000000049e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4f70
R13: 00000000ffffffff R14: 00007fd42b3226d4 R15: 0000000000000000

Fixes: 4512c43eac7e ("ipv6: remove null_entry before adding default route")
Signed-off-by: Wei Wang <weiwan@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv6/ip6_fib.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 9dcc3924a975..217683d40f12 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1226,8 +1226,14 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
 		}
 
 		if (!rcu_access_pointer(fn->leaf)) {
-			atomic_inc(&rt->rt6i_ref);
-			rcu_assign_pointer(fn->leaf, rt);
+			if (fn->fn_flags & RTN_TL_ROOT) {
+				/* put back null_entry for root node */
+				rcu_assign_pointer(fn->leaf,
+					    info->nl_net->ipv6.ip6_null_entry);
+			} else {
+				atomic_inc(&rt->rt6i_ref);
+				rcu_assign_pointer(fn->leaf, rt);
+			}
 		}
 		fn = sn;
 	}
-- 
2.16.0.rc1.238.g530d649a79-goog

Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

[Martin KaFai Lau]

On Thu, Jan 18, 2018 at 10:40:03AM -0800, Wei Wang wrote:
> From: Wei Wang <weiwan@google.com>
> 
> After commit 4512c43eac7e, if we add a route to the subtree of tb6_root
> which does not have any route attached to it yet, the current code will
> let tb6_root and the node in the subtree share the same route.
> This could cause problem cause tb6_root has RTN_INFO flag marked and the
You meant the RTN_RTINFO check in fib6_purge_rt()?

> tree repair and clean up code will not work properly.
> This commit makes sure tb6_root->leaf points back to null_entry instead
> of sharing route with other node.
> 
> It fixes the following syzkaller reported issue:
> BUG: KASAN: use-after-free in ipv6_prefix_equal include/net/ipv6.h:540 [inline]
> BUG: KASAN: use-after-free in fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
> Read of size 8 at addr ffff8801bc043498 by task syz-executor5/19819
> 
> CPU: 1 PID: 19819 Comm: syz-executor5 Not tainted 4.15.0-rc7+ #186
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>  kasan_report_error mm/kasan/report.c:351 [inline]
>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>  ipv6_prefix_equal include/net/ipv6.h:540 [inline]
>  fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
>  fib6_add+0x5fa/0x1540 net/ipv6/ip6_fib.c:1214
>  __ip6_ins_rt+0x6c/0x90 net/ipv6/route.c:1003
>  ip6_route_add+0x141/0x190 net/ipv6/route.c:2790
>  ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
>  inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
>  sock_do_ioctl+0x65/0xb0 net/socket.c:958
>  sock_ioctl+0x2c2/0x440 net/socket.c:1055
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
>  SYSC_ioctl fs/ioctl.c:701 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>  entry_SYSCALL_64_fastpath+0x23/0x9a
> RIP: 0033:0x452ac9
> RSP: 002b:00007fd42b321c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
> RDX: 0000000020fd7000 RSI: 000000000000890b RDI: 0000000000000013
> RBP: 000000000000049e R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4f70
> R13: 00000000ffffffff R14: 00007fd42b3226d4 R15: 0000000000000000
> 
> Fixes: 4512c43eac7e ("ipv6: remove null_entry before adding default route")
> Signed-off-by: Wei Wang <weiwan@google.com>
> Acked-by: Eric Dumazet <edumazet@google.com>
> ---
>  net/ipv6/ip6_fib.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index 9dcc3924a975..217683d40f12 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -1226,8 +1226,14 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
>  		}
>  
>  		if (!rcu_access_pointer(fn->leaf)) {
> -			atomic_inc(&rt->rt6i_ref);
> -			rcu_assign_pointer(fn->leaf, rt);
> +			if (fn->fn_flags & RTN_TL_ROOT) {
> +				/* put back null_entry for root node */
> +				rcu_assign_pointer(fn->leaf,
> +					    info->nl_net->ipv6.ip6_null_entry);
> +			} else {
> +				atomic_inc(&rt->rt6i_ref);
> +				rcu_assign_pointer(fn->leaf, rt);
> +			}
>  		}
>  		fn = sn;
>  	}
> -- 
> 2.16.0.rc1.238.g530d649a79-goog
> 

Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

[Wei Wang]

On Thu, Jan 18, 2018 at 2:47 PM, Martin KaFai Lau <kafai@fb.com> wrote:
> On Thu, Jan 18, 2018 at 10:40:03AM -0800, Wei Wang wrote:
>> From: Wei Wang <weiwan@google.com>
>>
>> After commit 4512c43eac7e, if we add a route to the subtree of tb6_root
>> which does not have any route attached to it yet, the current code will
>> let tb6_root and the node in the subtree share the same route.
>> This could cause problem cause tb6_root has RTN_INFO flag marked and the
> You meant the RTN_RTINFO check in fib6_purge_rt()?
>
Yes. Exactly.

>> tree repair and clean up code will not work properly.
>> This commit makes sure tb6_root->leaf points back to null_entry instead
>> of sharing route with other node.
>>
>> It fixes the following syzkaller reported issue:
>> BUG: KASAN: use-after-free in ipv6_prefix_equal include/net/ipv6.h:540 [inline]
>> BUG: KASAN: use-after-free in fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
>> Read of size 8 at addr ffff8801bc043498 by task syz-executor5/19819
>>
>> CPU: 1 PID: 19819 Comm: syz-executor5 Not tainted 4.15.0-rc7+ #186
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:17 [inline]
>>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>>  kasan_report_error mm/kasan/report.c:351 [inline]
>>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>>  ipv6_prefix_equal include/net/ipv6.h:540 [inline]
>>  fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
>>  fib6_add+0x5fa/0x1540 net/ipv6/ip6_fib.c:1214
>>  __ip6_ins_rt+0x6c/0x90 net/ipv6/route.c:1003
>>  ip6_route_add+0x141/0x190 net/ipv6/route.c:2790
>>  ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
>>  inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
>>  sock_do_ioctl+0x65/0xb0 net/socket.c:958
>>  sock_ioctl+0x2c2/0x440 net/socket.c:1055
>>  vfs_ioctl fs/ioctl.c:46 [inline]
>>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
>>  SYSC_ioctl fs/ioctl.c:701 [inline]
>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>>  entry_SYSCALL_64_fastpath+0x23/0x9a
>> RIP: 0033:0x452ac9
>> RSP: 002b:00007fd42b321c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
>> RDX: 0000000020fd7000 RSI: 000000000000890b RDI: 0000000000000013
>> RBP: 000000000000049e R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4f70
>> R13: 00000000ffffffff R14: 00007fd42b3226d4 R15: 0000000000000000
>>
>> Fixes: 4512c43eac7e ("ipv6: remove null_entry before adding default route")
>> Signed-off-by: Wei Wang <weiwan@google.com>
>> Acked-by: Eric Dumazet <edumazet@google.com>
>> ---
>>  net/ipv6/ip6_fib.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
>> index 9dcc3924a975..217683d40f12 100644
>> --- a/net/ipv6/ip6_fib.c
>> +++ b/net/ipv6/ip6_fib.c
>> @@ -1226,8 +1226,14 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
>>               }
>>
>>               if (!rcu_access_pointer(fn->leaf)) {
>> -                     atomic_inc(&rt->rt6i_ref);
>> -                     rcu_assign_pointer(fn->leaf, rt);
>> +                     if (fn->fn_flags & RTN_TL_ROOT) {
>> +                             /* put back null_entry for root node */
>> +                             rcu_assign_pointer(fn->leaf,
>> +                                         info->nl_net->ipv6.ip6_null_entry);
>> +                     } else {
>> +                             atomic_inc(&rt->rt6i_ref);
>> +                             rcu_assign_pointer(fn->leaf, rt);
>> +                     }
>>               }
>>               fn = sn;
>>       }
>> --
>> 2.16.0.rc1.238.g530d649a79-goog
>>

Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

[Martin KaFai Lau]

On Thu, Jan 18, 2018 at 03:31:29PM -0800, Wei Wang wrote:
> On Thu, Jan 18, 2018 at 2:47 PM, Martin KaFai Lau <kafai@fb.com> wrote:
> > On Thu, Jan 18, 2018 at 10:40:03AM -0800, Wei Wang wrote:
> >> From: Wei Wang <weiwan@google.com>
> >>
> >> After commit 4512c43eac7e, if we add a route to the subtree of tb6_root
> >> which does not have any route attached to it yet, the current code will
> >> let tb6_root and the node in the subtree share the same route.
> >> This could cause problem cause tb6_root has RTN_INFO flag marked and the
> > You meant the RTN_RTINFO check in fib6_purge_rt()?
> >
> Yes. Exactly.
Looks good to me.  Thanks for the fix!

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

Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

[Ido Schimmel]

Hi Wei, Martin,

On Thu, Jan 18, 2018 at 03:31:29PM -0800, Wei Wang wrote:
> On Thu, Jan 18, 2018 at 2:47 PM, Martin KaFai Lau <kafai@fb.com> wrote:
> > On Thu, Jan 18, 2018 at 10:40:03AM -0800, Wei Wang wrote:
> >> From: Wei Wang <weiwan@google.com>
> >>
> >> After commit 4512c43eac7e, if we add a route to the subtree of tb6_root
> >> which does not have any route attached to it yet, the current code will
> >> let tb6_root and the node in the subtree share the same route.
> >> This could cause problem cause tb6_root has RTN_INFO flag marked and the
> > You meant the RTN_RTINFO check in fib6_purge_rt()?
> >
> Yes. Exactly.

The check in fib6_purge_rt() is indeed problematic as tb6_root will not
release its reference on the deleted route. I can easily reproduce that
on my system. However, I don't understand how come we end up with a
use-after-free given tb6_root takes a reference on the route?

Thanks

> 
> >> tree repair and clean up code will not work properly.
> >> This commit makes sure tb6_root->leaf points back to null_entry instead
> >> of sharing route with other node.
> >>
> >> It fixes the following syzkaller reported issue:
> >> BUG: KASAN: use-after-free in ipv6_prefix_equal include/net/ipv6.h:540 [inline]
> >> BUG: KASAN: use-after-free in fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
> >> Read of size 8 at addr ffff8801bc043498 by task syz-executor5/19819
> >>
> >> CPU: 1 PID: 19819 Comm: syz-executor5 Not tainted 4.15.0-rc7+ #186
> >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> >> Call Trace:
> >>  __dump_stack lib/dump_stack.c:17 [inline]
> >>  dump_stack+0x194/0x257 lib/dump_stack.c:53
> >>  print_address_description+0x73/0x250 mm/kasan/report.c:252
> >>  kasan_report_error mm/kasan/report.c:351 [inline]
> >>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
> >>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
> >>  ipv6_prefix_equal include/net/ipv6.h:540 [inline]
> >>  fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
> >>  fib6_add+0x5fa/0x1540 net/ipv6/ip6_fib.c:1214
> >>  __ip6_ins_rt+0x6c/0x90 net/ipv6/route.c:1003
> >>  ip6_route_add+0x141/0x190 net/ipv6/route.c:2790
> >>  ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
> >>  inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
> >>  sock_do_ioctl+0x65/0xb0 net/socket.c:958
> >>  sock_ioctl+0x2c2/0x440 net/socket.c:1055
> >>  vfs_ioctl fs/ioctl.c:46 [inline]
> >>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
> >>  SYSC_ioctl fs/ioctl.c:701 [inline]
> >>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
> >>  entry_SYSCALL_64_fastpath+0x23/0x9a
> >> RIP: 0033:0x452ac9
> >> RSP: 002b:00007fd42b321c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
> >> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
> >> RDX: 0000000020fd7000 RSI: 000000000000890b RDI: 0000000000000013
> >> RBP: 000000000000049e R08: 0000000000000000 R09: 0000000000000000
> >> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4f70
> >> R13: 00000000ffffffff R14: 00007fd42b3226d4 R15: 0000000000000000
> >>
> >> Fixes: 4512c43eac7e ("ipv6: remove null_entry before adding default route")
> >> Signed-off-by: Wei Wang <weiwan@google.com>
> >> Acked-by: Eric Dumazet <edumazet@google.com>
> >> ---
> >>  net/ipv6/ip6_fib.c | 10 ++++++++--
> >>  1 file changed, 8 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> >> index 9dcc3924a975..217683d40f12 100644
> >> --- a/net/ipv6/ip6_fib.c
> >> +++ b/net/ipv6/ip6_fib.c
> >> @@ -1226,8 +1226,14 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
> >>               }
> >>
> >>               if (!rcu_access_pointer(fn->leaf)) {
> >> -                     atomic_inc(&rt->rt6i_ref);
> >> -                     rcu_assign_pointer(fn->leaf, rt);
> >> +                     if (fn->fn_flags & RTN_TL_ROOT) {
> >> +                             /* put back null_entry for root node */
> >> +                             rcu_assign_pointer(fn->leaf,
> >> +                                         info->nl_net->ipv6.ip6_null_entry);
> >> +                     } else {
> >> +                             atomic_inc(&rt->rt6i_ref);
> >> +                             rcu_assign_pointer(fn->leaf, rt);
> >> +                     }
> >>               }
> >>               fn = sn;
> >>       }
> >> --
> >> 2.16.0.rc1.238.g530d649a79-goog
> >>

Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

[Wei Wang]

On Fri, Jan 19, 2018 at 1:36 PM, Wei Wang <weiwan@google.com> wrote:
>
>
> On Fri, Jan 19, 2018 at 1:13 PM, Ido Schimmel <idosch@idosch.org> wrote:
>> Hi Wei, Martin,
>>
>> On Thu, Jan 18, 2018 at 03:31:29PM -0800, Wei Wang wrote:
>>> On Thu, Jan 18, 2018 at 2:47 PM, Martin KaFai Lau <kafai@fb.com> wrote:
>>> > On Thu, Jan 18, 2018 at 10:40:03AM -0800, Wei Wang wrote:
>>> >> From: Wei Wang <weiwan@google.com>
>>> >>
>>> >> After commit 4512c43eac7e, if we add a route to the subtree of
>>> >> tb6_root
>>> >> which does not have any route attached to it yet, the current code
>>> >> will
>>> >> let tb6_root and the node in the subtree share the same route.
>>> >> This could cause problem cause tb6_root has RTN_INFO flag marked and
>>> >> the
>>> > You meant the RTN_RTINFO check in fib6_purge_rt()?
>>> >
>>> Yes. Exactly.
>>
>> The check in fib6_purge_rt() is indeed problematic as tb6_root will not
>> release its reference on the deleted route. I can easily reproduce that
>> on my system. However, I don't understand how come we end up with a
>> use-after-free given tb6_root takes a reference on the route?
>>

(Resending with plain txt format)

Hi Ido,

I think the use-after-free does not really happen on the route that is being
falsely shared, but on the route which that route's rt6i_next is pointing to.
Nothing could prevent rt->rt6i_next from being released.

Thanks.
Wei

>> Thanks
>>
>>>
>>> >> tree repair and clean up code will not work properly.
>>> >> This commit makes sure tb6_root->leaf points back to null_entry
>>> >> instead
>>> >> of sharing route with other node.
>>> >>
>>> >> It fixes the following syzkaller reported issue:
>>> >> BUG: KASAN: use-after-free in ipv6_prefix_equal include/net/ipv6.h:540
>>> >> [inline]
>>> >> BUG: KASAN: use-after-free in fib6_add_1+0x165f/0x1790
>>> >> net/ipv6/ip6_fib.c:618
>>> >> Read of size 8 at addr ffff8801bc043498 by task syz-executor5/19819
>>> >>
>>> >> CPU: 1 PID: 19819 Comm: syz-executor5 Not tainted 4.15.0-rc7+ #186
>>> >> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>> >> BIOS Google 01/01/2011
>>> >> Call Trace:
>>> >>  __dump_stack lib/dump_stack.c:17 [inline]
>>> >>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>>> >>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>>> >>  kasan_report_error mm/kasan/report.c:351 [inline]
>>> >>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>>> >>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>>> >>  ipv6_prefix_equal include/net/ipv6.h:540 [inline]
>>> >>  fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
>>> >>  fib6_add+0x5fa/0x1540 net/ipv6/ip6_fib.c:1214
>>> >>  __ip6_ins_rt+0x6c/0x90 net/ipv6/route.c:1003
>>> >>  ip6_route_add+0x141/0x190 net/ipv6/route.c:2790
>>> >>  ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
>>> >>  inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
>>> >>  sock_do_ioctl+0x65/0xb0 net/socket.c:958
>>> >>  sock_ioctl+0x2c2/0x440 net/socket.c:1055
>>> >>  vfs_ioctl fs/ioctl.c:46 [inline]
>>> >>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
>>> >>  SYSC_ioctl fs/ioctl.c:701 [inline]
>>> >>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>>> >>  entry_SYSCALL_64_fastpath+0x23/0x9a
>>> >> RIP: 0033:0x452ac9
>>> >> RSP: 002b:00007fd42b321c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
>>> >> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
>>> >> RDX: 0000000020fd7000 RSI: 000000000000890b RDI: 0000000000000013
>>> >> RBP: 000000000000049e R08: 0000000000000000 R09: 0000000000000000
>>> >> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4f70
>>> >> R13: 00000000ffffffff R14: 00007fd42b3226d4 R15: 0000000000000000
>>> >>
>>> >> Fixes: 4512c43eac7e ("ipv6: remove null_entry before adding default
>>> >> route")
>>> >> Signed-off-by: Wei Wang <weiwan@google.com>
>>> >> Acked-by: Eric Dumazet <edumazet@google.com>
>>> >> ---
>>> >>  net/ipv6/ip6_fib.c | 10 ++++++++--
>>> >>  1 file changed, 8 insertions(+), 2 deletions(-)
>>> >>
>>> >> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
>>> >> index 9dcc3924a975..217683d40f12 100644
>>> >> --- a/net/ipv6/ip6_fib.c
>>> >> +++ b/net/ipv6/ip6_fib.c
>>> >> @@ -1226,8 +1226,14 @@ int fib6_add(struct fib6_node *root, struct
>>> >> rt6_info *rt,
>>> >>               }
>>> >>
>>> >>               if (!rcu_access_pointer(fn->leaf)) {
>>> >> -                     atomic_inc(&rt->rt6i_ref);
>>> >> -                     rcu_assign_pointer(fn->leaf, rt);
>>> >> +                     if (fn->fn_flags & RTN_TL_ROOT) {
>>> >> +                             /* put back null_entry for root node */
>>> >> +                             rcu_assign_pointer(fn->leaf,
>>> >> +
>>> >> info->nl_net->ipv6.ip6_null_entry);
>>> >> +                     } else {
>>> >> +                             atomic_inc(&rt->rt6i_ref);
>>> >> +                             rcu_assign_pointer(fn->leaf, rt);
>>> >> +                     }
>>> >>               }
>>> >>               fn = sn;
>>> >>       }
>>> >> --
>>> >> 2.16.0.rc1.238.g530d649a79-goog
>>> >>
>

Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

[Ido Schimmel]

On Fri, Jan 19, 2018 at 01:46:02PM -0800, Wei Wang wrote:
> On Fri, Jan 19, 2018 at 1:36 PM, Wei Wang <weiwan@google.com> wrote:
> >
> >
> > On Fri, Jan 19, 2018 at 1:13 PM, Ido Schimmel <idosch@idosch.org> wrote:
> >> Hi Wei, Martin,
> >>
> >> On Thu, Jan 18, 2018 at 03:31:29PM -0800, Wei Wang wrote:
> >>> On Thu, Jan 18, 2018 at 2:47 PM, Martin KaFai Lau <kafai@fb.com> wrote:
> >>> > On Thu, Jan 18, 2018 at 10:40:03AM -0800, Wei Wang wrote:
> >>> >> From: Wei Wang <weiwan@google.com>
> >>> >>
> >>> >> After commit 4512c43eac7e, if we add a route to the subtree of
> >>> >> tb6_root
> >>> >> which does not have any route attached to it yet, the current code
> >>> >> will
> >>> >> let tb6_root and the node in the subtree share the same route.
> >>> >> This could cause problem cause tb6_root has RTN_INFO flag marked and
> >>> >> the
> >>> > You meant the RTN_RTINFO check in fib6_purge_rt()?
> >>> >
> >>> Yes. Exactly.
> >>
> >> The check in fib6_purge_rt() is indeed problematic as tb6_root will not
> >> release its reference on the deleted route. I can easily reproduce that
> >> on my system. However, I don't understand how come we end up with a
> >> use-after-free given tb6_root takes a reference on the route?
> >>
> 
> (Resending with plain txt format)
> 
> Hi Ido,
> 
> I think the use-after-free does not really happen on the route that is being
> falsely shared, but on the route which that route's rt6i_next is pointing to.
> Nothing could prevent rt->rt6i_next from being released.

Yep, I considered it, then confused myself and disqualified the
possibility, but you're right. FWIW, here's the reproducer:

ip -6 route add default from 2001:db8::/64 dev dummy0 metric 1
ip -6 route append default from 2001:db8::/64 dev dummy0 metric 2
ip -6 route del default from 2001:db8::/64 dev dummy0 metric 1
ip -6 route del default from 2001:db8::/64 dev dummy0 metric 2
ip -6 route show

Thanks!

Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

[David Miller]

From: Wei Wang <weiwan@google.com>
Date: Thu, 18 Jan 2018 10:40:03 -0800

> From: Wei Wang <weiwan@google.com>
> 
> After commit 4512c43eac7e, if we add a route to the subtree of tb6_root
> which does not have any route attached to it yet, the current code will
> let tb6_root and the node in the subtree share the same route.
> This could cause problem cause tb6_root has RTN_INFO flag marked and the
> tree repair and clean up code will not work properly.
> This commit makes sure tb6_root->leaf points back to null_entry instead
> of sharing route with other node.
> 
> It fixes the following syzkaller reported issue:
 ...
> Fixes: 4512c43eac7e ("ipv6: remove null_entry before adding default route")
> Signed-off-by: Wei Wang <weiwan@google.com>
> Acked-by: Eric Dumazet <edumazet@google.com>

Applied, thank you.