Re: [PATCH] net: tls: fix possible race condition between do_tls_getsockopt_conf() and do_tls_setsockopt_conf()

Florian Westphal
2023-02-24T12:06:49Z

Hangyu Hua <hbh25y@gmail.com> wrote:
> ctx->crypto_send.info is not protected by lock_sock in
> do_tls_getsockopt_conf(). A race condition between do_tls_getsockopt_conf()
> and do_tls_setsockopt_conf() can cause a NULL point dereference or
> use-after-free read when memcpy.

Its good practice to quote the relevant parts of the splat here.

> Fixes: 3c4d7559159b ("tls: kernel TLS support")
> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
> ---
> net/tls/tls_main.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> index 3735cb00905d..4956f5149b8e 100644
> --- a/net/tls/tls_main.c
> +++ b/net/tls/tls_main.c
> @@ -374,6 +374,7 @@ static int do_tls_getsockopt_conf(struct sock *sk, char __user *optval,
> }
>
> /* get user crypto info */
> + lock_sock(sk);
> if (tx) {
> crypto_info = &ctx->crypto_send.info;
> cctx = &ctx->tx;
> @@ -381,6 +382,7 @@ static int do_tls_getsockopt_conf(struct sock *sk, char __user *optval,
> crypto_info = &ctx->crypto_recv.info;
> cctx = &ctx->rx;
> }
> + release_sock(sk);

Could you elaborate how this fixes a UAF bug?

AFAIU do_tls_setsockopt_conf uses ctx-> as scratch space, but this means
that getsockopt can see partial states.

If so, can the setsockopt part be changed so that reads only see
consistent states?