Re: [PATCH net] net: socket: set sock->sk to NULL after calling proto_ops::release()
From: Cong Wang
Date: Fri Feb 22 2019 - 13:06:11 EST
On Thu, Feb 21, 2019 at 2:14 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx> # v4.10+
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Acked-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>