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 <[email protected]>
---
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
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 <[email protected]>
> ---
> 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) {
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 <[email protected]>
>> ---
>> 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) {
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 <[email protected]>
>>> ---
>>> 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) {
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 <[email protected]>
>>>> ---
>>>> 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) {
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 <[email protected]>
>>>>> ---
>>>>> 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) {
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 ?
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 ?
>