linux-kernel - Re: [PATCH net-next v3 03/11] tls/sw: Use zero-length sendmsg() without MSG

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Message-ID: <ZHtTdEyIjtgg3nAo@corigine.com>
Date:   Sat, 3 Jun 2023 16:51:32 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Dan Carpenter <dan.carpenter@...aro.org>
Cc:     David Howells <dhowells@...hat.com>, netdev@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Boris Pismenny <borisp@...dia.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 03/11] tls/sw: Use zero-length sendmsg()
 without MSG_MORE to flush

On Fri, Jun 02, 2023 at 10:00:45PM +0300, Dan Carpenter wrote:
> On Fri, Jun 02, 2023 at 08:27:56PM +0200, Simon Horman wrote:
> > + 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 <dhowells@...hat.com>
> > > cc: Chuck Lever <chuck.lever@...cle.com>
> > > cc: Boris Pismenny <borisp@...dia.com>
> > > cc: John Fastabend <john.fastabend@...il.com>
> > > cc: Jakub Kicinski <kuba@...nel.org>
> > > cc: Eric Dumazet <edumazet@...gle.com>
> > > cc: "David S. Miller" <davem@...emloft.net>
> > > cc: Paolo Abeni <pabeni@...hat.com>
> > > cc: Jens Axboe <axboe@...nel.dk>
> > > cc: Matthew Wilcox <willy@...radead.org>
> > > cc: netdev@...r.kernel.org
> > > ---
> > >  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
> 
> This warning seems correct to me.
> 
> >  * orig_size
> 
> This warning assumes we hit the first warning and then hit the goto
> wait_for_memory;
> 
> >  * msg_en
> 
> I don't get this warning on my system but it's the same thing.  Hit the
> first warning then the goto wait_for_memory.
> 
> >  * required_size
> 
> Same.
> 
> >  * try_to_copy
> 
> I don't really understand this warning and I can't reproduce it.
> Strange.

Thanks Dan.

Of the above I think only the last one was flagged
by GCC but not Smatch. I can try investigating further if it is useful.