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

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Date: Tue, 09 Jan 2024 15:22:39 -0800
From: John Fastabend <john.fastabend@...il.com>
To: 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

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;
                }