netdev - Re: [PATCH net] sctp: prevent info leak in sctp_make

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Date:   Tue, 29 Jun 2021 10:23:49 +0200
From:   Andreas Fink <afink@...t.fink.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Vlad Yasevich <vyasevich@...il.com>,
        Xin Long <lucien.xin@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-sctp@...r.kernel.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] sctp: prevent info leak in sctp_make_heartbeat()

Does that gcc extension work with all compilers, especially clang?

Dan Carpenter wrote on 29.06.21 10:19:
> The "hbinfo" struct has a 4 byte hole at the end so we have to zero it
> out to prevent stack information from being disclosed.
>
> Fixes: fe59379b9ab7 ("sctp: do the basic send and recv for PLPMTUD probe")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> Btw = {} is the newest way to initialize holes.
>
> In the past we have debated whether = {} will *always* zero out struct
> holes and it wasn't clear from the C standard.  But it turns out that
> "= {}" is not part of the standard but is instead a GCC extension and it
> does clear the holes.  In GCC (not the C standard) then = {0}; is also
> supposed to initialize holes in there was a bug in one version where it
> didn't.
>
> So that's nice, because adding memset()s to zero everywhere was ugly.
>
>  net/sctp/sm_make_chunk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index 587fb3cb88e2..3a290f620e96 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -1162,7 +1162,7 @@ struct sctp_chunk *sctp_make_new_encap_port(const struct sctp_association *asoc,
>  struct sctp_chunk *sctp_make_heartbeat(const struct sctp_association *asoc,
>  				       const struct sctp_transport *transport)
>  {
> -	struct sctp_sender_hb_info hbinfo;
> +	struct sctp_sender_hb_info hbinfo = {};
>  	struct sctp_chunk *retval;
>  
>  	retval = sctp_make_control(asoc, SCTP_CID_HEARTBEAT, 0,