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SubjectRe: [PATCH net] ax25: use after free in ax25_connect
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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) {

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