Subject: Re: [PATCH net-next v3 03/11] tls/sw: Use zero-length sendmsg() without MSG_MORE to flush

From: Simon Horman <[email-masked]>
Date: Fri, 2 Jun 2023 20:27:56 +0200

+ dan Carpenter

On Fri, Jun 02, 2023 at 04:07:44PM +0100, David Howells wrote:
> Allow userspace to end a TLS record without supplying any data by calling
> send()/sendto()/sendmsg() with no data and no MSG_MORE flag.  This can be
> used to flush a previous send/splice that had MSG_MORE or SPLICE_F_MORE set
> or a sendfile() that was incomplete.
> 
> Without this, a zero-length send to tls-sw is just ignored.  I think
> tls-device will do the right thing without modification.
> 
> Signed-off-by: David Howells <[email-masked]>
> cc: Chuck Lever <[email-masked]>
> cc: Boris Pismenny <[email-masked]>
> cc: John Fastabend <[email-masked]>
> cc: Jakub Kicinski <[email-masked]>
> cc: Eric Dumazet <[email-masked]>
> cc: "David S. Miller" <[email-masked]>
> cc: Paolo Abeni <[email-masked]>
> cc: Jens Axboe <[email-masked]>
> cc: Matthew Wilcox <[email-masked]>
> cc: [email-masked]
> ---
>  net/tls/tls_sw.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index cac1adc968e8..6aa6d17888f5 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -945,7 +945,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>  	struct tls_rec *rec;
>  	int required_size;
>  	int num_async = 0;
> -	bool full_record;
> +	bool full_record = false;
>  	int record_room;
>  	int num_zc = 0;
>  	int orig_size;
> @@ -971,6 +971,9 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>  		}
>  	}
>  
> +	if (!msg_data_left(msg) && eor)
> +		goto just_flush;
> +

Hi David,

the flow of this function is not entirely simple, so it is not easy for me
to manually verify this. But in combination gcc-12 -Wmaybe-uninitialized
and Smatch report that the following may be used uninitialised as a result
of this change:

 * msg_pl
 * orig_size
 * msg_en
 * required_size
 * try_to_copy

>  	while (msg_data_left(msg)) {
>  		if (sk->sk_err) {
>  			ret = -sk->sk_err;
> @@ -1082,6 +1085,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>  		 */
>  		tls_ctx->pending_open_record_frags = true;
>  		copied += try_to_copy;
> +just_flush:
>  		if (full_record || eor) {
>  			ret = bpf_exec_tx_verdict(msg_pl, sk, full_record,
>  						  record_type, &copied,
> 
>