linux-kernel - RE: [PATCH] tls: fix WARNING in __sk_msg

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Date: Tue, 09 Jan 2024 23:53:28 -0800
From: John Fastabend <john.fastabend@...il.com>
To: John Fastabend <john.fastabend@...il.com>, 
 Edward Adam Davis <eadavis@...com>, 
 syzbot+f2977222e0e95cec15c8@...kaller.appspotmail.com
Cc: andrii@...nel.org, 
 ast@...nel.org, 
 borisp@...dia.com, 
 bpf@...r.kernel.org, 
 daniel@...earbox.net, 
 davem@...emloft.net, 
 dhowells@...hat.com, 
 edumazet@...gle.com, 
 jakub@...udflare.com, 
 john.fastabend@...il.com, 
 kuba@...nel.org, 
 linux-kernel@...r.kernel.org, 
 netdev@...r.kernel.org, 
 pabeni@...hat.com, 
 syzkaller-bugs@...glegroups.com
Subject: RE: [PATCH] tls: fix WARNING in __sk_msg_free

John Fastabend wrote:
> Edward Adam Davis wrote:
> > Syzbot constructed 32 scatterlists, and the data members in struct sk_msg_sg 
> > can only store a maximum of MAX_MSG_FRAGS scatterlists.
> > However, the value of MAX_MSG_FRAGS=CONFIG_MAX_SKB_FRAG is less than 32, which
> > leads to the warning reported here.
> > 
> > Prevent similar issues from occurring by checking whether sg.end is greater 
> > than MAX_MSG_FRAGS.
> > 
> > Reported-and-tested-by: syzbot+f2977222e0e95cec15c8@...kaller.appspotmail.com
> > Signed-off-by: Edward Adam Davis <eadavis@...com>
> > ---
> >  net/tls/tls_sw.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> > index e37b4d2e2acd..68dbe821f61d 100644
> > --- a/net/tls/tls_sw.c
> > +++ b/net/tls/tls_sw.c
> > @@ -1016,6 +1016,8 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
> >  
> >  		msg_pl = &rec->msg_plaintext;
> >  		msg_en = &rec->msg_encrypted;
> > +		if (msg_pl->sg.end >= MAX_MSG_FRAGS)
> > +			return -EINVAL;
> >  
> >  		orig_size = msg_pl->sg.size;
> >  		full_record = false;
> > -- 
> > 2.43.0
> > 
> 
> I'll test this in a bit, but I suspect this error is because even
> if the msg_pl is full (the sg.end == MAX_MSG_FRAGS) the code is
> missing a full_record=true set to force the loop to do the send
> and abort. My opinion is we should never iterated the loop if the
> msg_pl was full.
> 
> I think something like this is actually needed.
> 
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index e37b4d2e2acd..9cfa6f8d51e3 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -1052,8 +1052,10 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
>                         if (ret < 0)
>                                 goto send_end;
>                         tls_ctx->pending_open_record_frags = true;
> -                       if (full_record || eor || sk_msg_full(msg_pl))
> +                       if (full_record || eor || sk_msg_full(msg_pl)) {
> +                               full_record = true;
>                                 goto copied;
> +                       }
>                         continue;
>                 }

Actually, it needs a bit more than above. That will fix the warning,
but it returns an error on when it should flush the full_record in
some cases. I'll send a fix shortly.