Re: [PATCH net] net: socket: set sock->sk to NULL after calling proto_ops::release()

[Cong Wang <xiyou.wangcong@gmail.com>]

On Thu, Feb 21, 2019 at 2:14 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> Commit 9060cb719e61 ("net: crypto set sk to NULL when af_alg_release.")
> fixed a use-after-free in sockfs_setattr() when an AF_ALG socket is
> closed concurrently with fchownat().  However, it ignored that many
> other proto_ops::release() methods don't set sock->sk to NULL and
> therefore allow the same use-after-free:
>
>     - base_sock_release
>     - bnep_sock_release
>     - cmtp_sock_release
>     - data_sock_release
>     - dn_release
>     - hci_sock_release
>     - hidp_sock_release
>     - iucv_sock_release
>     - l2cap_sock_release
>     - llcp_sock_release
>     - llc_ui_release
>     - rawsock_release
>     - rfcomm_sock_release
>     - sco_sock_release
>     - svc_release
>     - vcc_release
>     - x25_release
>
> Rather than fixing all these and relying on every socket type to get
> this right forever, just make __sock_release() set sock->sk to NULL
> itself after calling proto_ops::release().
>
> Reproducer that produces the KASAN splat when any of these socket types
> are configured into the kernel:
>
>     #include <pthread.h>
>     #include <stdlib.h>
>     #include <sys/socket.h>
>     #include <unistd.h>
>
>     pthread_t t;
>     volatile int fd;
>
>     void *close_thread(void *arg)
>     {
>         for (;;) {
>             usleep(rand() % 100);
>             close(fd);
>         }
>     }
>
>     int main()
>     {
>         pthread_create(&t, NULL, close_thread, NULL);
>         for (;;) {
>             fd = socket(rand() % 50, rand() % 11, 0);
>             fchownat(fd, "", 1000, 1000, 0x1000);
>             close(fd);
>         }
>     }
>
> Fixes: 86741ec25462 ("net: core: Add a UID field to struct sock.")
> Cc: <stable@vger.kernel.org> # v4.10+
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Acked-by: Cong Wang <xiyou.wangcong@gmail.com>