[PATCH net] ax25: use after free in ax25_connect

[PATCH net] ax25: use after free in ax25_connect

[Hangyu Hua]

sk_to_ax25(sk) needs to be called after lock_sock(sk) to avoid UAF
caused by a race condition.

Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
---
 net/ax25/af_ax25.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index cfca99e295b8..c5d62420a2a8 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1127,7 +1127,7 @@ static int __must_check ax25_connect(struct socket *sock,
 	struct sockaddr *uaddr, int addr_len, int flags)
 {
 	struct sock *sk = sock->sk;
-	ax25_cb *ax25 = sk_to_ax25(sk), *ax25t;
+	ax25_cb *ax25, *ax25t;
 	struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 *)uaddr;
 	ax25_digi *digi = NULL;
 	int ct = 0, err = 0;
@@ -1155,6 +1155,8 @@ static int __must_check ax25_connect(struct socket *sock,
 
 	lock_sock(sk);
 
+	ax25 = sk_to_ax25(sk);
+
 	/* deal with restarts */
 	if (sock->state == SS_CONNECTING) {
 		switch (sk->sk_state) {
-- 
2.25.1

Re: [PATCH net] ax25: use after free in ax25_connect

[Eric Dumazet]

On 1/10/22 20:20, Hangyu Hua wrote:
> sk_to_ax25(sk) needs to be called after lock_sock(sk) to avoid UAF
> caused by a race condition.

Can you describe what race condition you have found exactly ?

sk pointer can not change.


> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
> ---
>   net/ax25/af_ax25.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
> index cfca99e295b8..c5d62420a2a8 100644
> --- a/net/ax25/af_ax25.c
> +++ b/net/ax25/af_ax25.c
> @@ -1127,7 +1127,7 @@ static int __must_check ax25_connect(struct socket *sock,
>   	struct sockaddr *uaddr, int addr_len, int flags)
>   {
>   	struct sock *sk = sock->sk;
> -	ax25_cb *ax25 = sk_to_ax25(sk), *ax25t;
> +	ax25_cb *ax25, *ax25t;
>   	struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 *)uaddr;
>   	ax25_digi *digi = NULL;
>   	int ct = 0, err = 0;
> @@ -1155,6 +1155,8 @@ static int __must_check ax25_connect(struct socket *sock,
>   
>   	lock_sock(sk);
>   
> +	ax25 = sk_to_ax25(sk);
> +
>   	/* deal with restarts */
>   	if (sock->state == SS_CONNECTING) {
>   		switch (sk->sk_state) {

Re: [PATCH net] ax25: use after free in ax25_connect

[Hangyu Hua]

I try to use ax25_release to trigger this bug like this:
ax25_release                 ax25_connect
lock_sock(sk);
-----------------------------sk = sock->sk;
-----------------------------ax25 = sk_to_ax25(sk);
ax25_destroy_socket(ax25);
release_sock(sk);
-----------------------------lock_sock(sk);
-----------------------------use ax25 again

But i failed beacause their have large speed difference. And i
don't have a physical device to test other function in ax25.
Anyway, i still think there will have a function to trigger this
race condition like ax25_destroy_timer. Beacause Any ohter
functions in ax25_proto_ops like ax25_bind protect ax25_sock by 
lock_sock(sk).

Thanks.




On 2022/1/12 上午4:56, Eric Dumazet wrote:
> 
> On 1/10/22 20:20, Hangyu Hua wrote:
>> sk_to_ax25(sk) needs to be called after lock_sock(sk) to avoid UAF
>> caused by a race condition.
> 
> Can you describe what race condition you have found exactly ?
> 
> sk pointer can not change.
> 
> 
>> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
>> ---
>>   net/ax25/af_ax25.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
>> index cfca99e295b8..c5d62420a2a8 100644
>> --- a/net/ax25/af_ax25.c
>> +++ b/net/ax25/af_ax25.c
>> @@ -1127,7 +1127,7 @@ static int __must_check ax25_connect(struct 
>> socket *sock,
>>       struct sockaddr *uaddr, int addr_len, int flags)
>>   {
>>       struct sock *sk = sock->sk;
>> -    ax25_cb *ax25 = sk_to_ax25(sk), *ax25t;
>> +    ax25_cb *ax25, *ax25t;
>>       struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 
>> *)uaddr;
>>       ax25_digi *digi = NULL;
>>       int ct = 0, err = 0;
>> @@ -1155,6 +1155,8 @@ static int __must_check ax25_connect(struct 
>> socket *sock,
>>       lock_sock(sk);
>> +    ax25 = sk_to_ax25(sk);
>> +
>>       /* deal with restarts */
>>       if (sock->state == SS_CONNECTING) {
>>           switch (sk->sk_state) {

Re: [PATCH net] ax25: use after free in ax25_connect

[Eric Dumazet]

On 1/11/22 18:13, Hangyu Hua wrote:
> I try to use ax25_release to trigger this bug like this:
> ax25_release                 ax25_connect
> lock_sock(sk);
> -----------------------------sk = sock->sk;
> -----------------------------ax25 = sk_to_ax25(sk);
> ax25_destroy_socket(ax25);
> release_sock(sk);
> -----------------------------lock_sock(sk);
> -----------------------------use ax25 again
>
> But i failed beacause their have large speed difference. And i
> don't have a physical device to test other function in ax25.
> Anyway, i still think there will have a function to trigger this
> race condition like ax25_destroy_timer. Beacause Any ohter
> functions in ax25_proto_ops like ax25_bind protect ax25_sock by 
> lock_sock(sk).


For a given sk pointer, sk_to_ax25(sk) is always returning the same value,

regardless of sk lock being held or not.

ax25_sk(sk)->cb  is set only from ax25_create() or ax25_make_new()

ax25_connect can not be called until these operations have completed ?



>
> Thanks.
>
>
>
>
> On 2022/1/12 上午4:56, Eric Dumazet wrote:
>>
>> On 1/10/22 20:20, Hangyu Hua wrote:
>>> sk_to_ax25(sk) needs to be called after lock_sock(sk) to avoid UAF
>>> caused by a race condition.
>>
>> Can you describe what race condition you have found exactly ?
>>
>> sk pointer can not change.
>>
>>
>>> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
>>> ---
>>>   net/ax25/af_ax25.c | 4 +++-
>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
>>> index cfca99e295b8..c5d62420a2a8 100644
>>> --- a/net/ax25/af_ax25.c
>>> +++ b/net/ax25/af_ax25.c
>>> @@ -1127,7 +1127,7 @@ static int __must_check ax25_connect(struct 
>>> socket *sock,
>>>       struct sockaddr *uaddr, int addr_len, int flags)
>>>   {
>>>       struct sock *sk = sock->sk;
>>> -    ax25_cb *ax25 = sk_to_ax25(sk), *ax25t;
>>> +    ax25_cb *ax25, *ax25t;
>>>       struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 
>>> *)uaddr;
>>>       ax25_digi *digi = NULL;
>>>       int ct = 0, err = 0;
>>> @@ -1155,6 +1155,8 @@ static int __must_check ax25_connect(struct 
>>> socket *sock,
>>>       lock_sock(sk);
>>> +    ax25 = sk_to_ax25(sk);
>>> +
>>>       /* deal with restarts */
>>>       if (sock->state == SS_CONNECTING) {
>>>           switch (sk->sk_state) {

Re: [PATCH net] ax25: use after free in ax25_connect

[Hangyu Hua]

Yes.

And there are two ways to release ax25, ax25_release and time expiry. I 
tested that ax25_release will not be invoked before ax25_connect is done 
by closing fd from user space. I think the reason is that __sys_connect 
use fdget() to protect fd. But i can't test if a function like 
ax25_std_heartbeat_expiry will release ax25 between sk_to_ax25(sk) and 
lock_sock(sk).

So i think it's better to protect sk_to_ax25(sk) by a lock. Beacause 
functions like ax25_release use sk_to_ax25 after a lock.


On 2022/1/12 下午5:59, Eric Dumazet wrote:
> 
> On 1/11/22 18:13, Hangyu Hua wrote:
>> I try to use ax25_release to trigger this bug like this:
>> ax25_release                 ax25_connect
>> lock_sock(sk);
>> -----------------------------sk = sock->sk;
>> -----------------------------ax25 = sk_to_ax25(sk);
>> ax25_destroy_socket(ax25);
>> release_sock(sk);
>> -----------------------------lock_sock(sk);
>> -----------------------------use ax25 again
>>
>> But i failed beacause their have large speed difference. And i
>> don't have a physical device to test other function in ax25.
>> Anyway, i still think there will have a function to trigger this
>> race condition like ax25_destroy_timer. Beacause Any ohter
>> functions in ax25_proto_ops like ax25_bind protect ax25_sock by 
>> lock_sock(sk).
> 
> 
> For a given sk pointer, sk_to_ax25(sk) is always returning the same value,
> 
> regardless of sk lock being held or not.
> 
> ax25_sk(sk)->cb  is set only from ax25_create() or ax25_make_new()
> 
> ax25_connect can not be called until these operations have completed ?
> 
> 
> 
>>
>> Thanks.
>>
>>
>>
>>
>> On 2022/1/12 上午4:56, Eric Dumazet wrote:
>>>
>>> On 1/10/22 20:20, Hangyu Hua wrote:
>>>> sk_to_ax25(sk) needs to be called after lock_sock(sk) to avoid UAF
>>>> caused by a race condition.
>>>
>>> Can you describe what race condition you have found exactly ?
>>>
>>> sk pointer can not change.
>>>
>>>
>>>> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
>>>> ---
>>>>   net/ax25/af_ax25.c | 4 +++-
>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
>>>> index cfca99e295b8..c5d62420a2a8 100644
>>>> --- a/net/ax25/af_ax25.c
>>>> +++ b/net/ax25/af_ax25.c
>>>> @@ -1127,7 +1127,7 @@ static int __must_check ax25_connect(struct 
>>>> socket *sock,
>>>>       struct sockaddr *uaddr, int addr_len, int flags)
>>>>   {
>>>>       struct sock *sk = sock->sk;
>>>> -    ax25_cb *ax25 = sk_to_ax25(sk), *ax25t;
>>>> +    ax25_cb *ax25, *ax25t;
>>>>       struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 
>>>> *)uaddr;
>>>>       ax25_digi *digi = NULL;
>>>>       int ct = 0, err = 0;
>>>> @@ -1155,6 +1155,8 @@ static int __must_check ax25_connect(struct 
>>>> socket *sock,
>>>>       lock_sock(sk);
>>>> +    ax25 = sk_to_ax25(sk);
>>>> +
>>>>       /* deal with restarts */
>>>>       if (sock->state == SS_CONNECTING) {
>>>>           switch (sk->sk_state) {

Re: [PATCH net] ax25: use after free in ax25_connect

[Hangyu Hua]

Any suggestions for this patch ? Guys.

I think putting sk_to_ax25 after lock_sock(sk) here will avoid any 
possilbe race conditions like other functions in ax25_proto_ops.

On 2022/1/12 下午7:11, Hangyu Hua wrote:
> Yes.
> 
> And there are two ways to release ax25, ax25_release and time expiry. I 
> tested that ax25_release will not be invoked before ax25_connect is done 
> by closing fd from user space. I think the reason is that __sys_connect 
> use fdget() to protect fd. But i can't test if a function like 
> ax25_std_heartbeat_expiry will release ax25 between sk_to_ax25(sk) and 
> lock_sock(sk).
> 
> So i think it's better to protect sk_to_ax25(sk) by a lock. Beacause 
> functions like ax25_release use sk_to_ax25 after a lock.
> 
> 
> On 2022/1/12 下午5:59, Eric Dumazet wrote:
>>
>> On 1/11/22 18:13, Hangyu Hua wrote:
>>> I try to use ax25_release to trigger this bug like this:
>>> ax25_release                 ax25_connect
>>> lock_sock(sk);
>>> -----------------------------sk = sock->sk;
>>> -----------------------------ax25 = sk_to_ax25(sk);
>>> ax25_destroy_socket(ax25);
>>> release_sock(sk);
>>> -----------------------------lock_sock(sk);
>>> -----------------------------use ax25 again
>>>
>>> But i failed beacause their have large speed difference. And i
>>> don't have a physical device to test other function in ax25.
>>> Anyway, i still think there will have a function to trigger this
>>> race condition like ax25_destroy_timer. Beacause Any ohter
>>> functions in ax25_proto_ops like ax25_bind protect ax25_sock by 
>>> lock_sock(sk).
>>
>>
>> For a given sk pointer, sk_to_ax25(sk) is always returning the same 
>> value,
>>
>> regardless of sk lock being held or not.
>>
>> ax25_sk(sk)->cb  is set only from ax25_create() or ax25_make_new()
>>
>> ax25_connect can not be called until these operations have completed ?
>>
>>
>>
>>>
>>> Thanks.
>>>
>>>
>>>
>>>
>>> On 2022/1/12 上午4:56, Eric Dumazet wrote:
>>>>
>>>> On 1/10/22 20:20, Hangyu Hua wrote:
>>>>> sk_to_ax25(sk) needs to be called after lock_sock(sk) to avoid UAF
>>>>> caused by a race condition.
>>>>
>>>> Can you describe what race condition you have found exactly ?
>>>>
>>>> sk pointer can not change.
>>>>
>>>>
>>>>> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
>>>>> ---
>>>>>   net/ax25/af_ax25.c | 4 +++-
>>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
>>>>> index cfca99e295b8..c5d62420a2a8 100644
>>>>> --- a/net/ax25/af_ax25.c
>>>>> +++ b/net/ax25/af_ax25.c
>>>>> @@ -1127,7 +1127,7 @@ static int __must_check ax25_connect(struct 
>>>>> socket *sock,
>>>>>       struct sockaddr *uaddr, int addr_len, int flags)
>>>>>   {
>>>>>       struct sock *sk = sock->sk;
>>>>> -    ax25_cb *ax25 = sk_to_ax25(sk), *ax25t;
>>>>> +    ax25_cb *ax25, *ax25t;
>>>>>       struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 
>>>>> *)uaddr;
>>>>>       ax25_digi *digi = NULL;
>>>>>       int ct = 0, err = 0;
>>>>> @@ -1155,6 +1155,8 @@ static int __must_check ax25_connect(struct 
>>>>> socket *sock,
>>>>>       lock_sock(sk);
>>>>> +    ax25 = sk_to_ax25(sk);
>>>>> +
>>>>>       /* deal with restarts */
>>>>>       if (sock->state == SS_CONNECTING) {
>>>>>           switch (sk->sk_state) {

Re: [PATCH net] ax25: use after free in ax25_connect

[Eric Dumazet]

On 1/13/22 22:54, Hangyu Hua wrote:
> Any suggestions for this patch ? Guys.
>
> I think putting sk_to_ax25 after lock_sock(sk) here will avoid any 
> possilbe race conditions like other functions in ax25_proto_ops. CTING) {
>

As explained, your patch is not needed.

You failed to describe how a race was possible.

Just moving code around wont help.

How about providing a stack trace or some syzbot repro ?

Re: [PATCH net] ax25: use after free in ax25_connect

[Hangyu Hua]

I get it.

Thanks.

On 2022/1/14 下午11:19, Eric Dumazet wrote:
> 
> On 1/13/22 22:54, Hangyu Hua wrote:
>> Any suggestions for this patch ? Guys.
>>
>> I think putting sk_to_ax25 after lock_sock(sk) here will avoid any 
>> possilbe race conditions like other functions in ax25_proto_ops. CTING) {
>>
> 
> As explained, your patch is not needed.
> 
> You failed to describe how a race was possible.
> 
> Just moving code around wont help.
> 
> How about providing a stack trace or some syzbot repro ?
>