netdev - Re: [PATCH net 1/2] net: tls, fix WARNIING in __sk_msg

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Message-ID: <20240111170513.7f8cd768@kernel.org>
Date: Thu, 11 Jan 2024 17:05:13 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: John Fastabend <john.fastabend@...il.com>
Cc: netdev@...r.kernel.org, eadavis@...com, bpf@...r.kernel.org,
 borisp@...dia.com
Subject: Re: [PATCH net 1/2] net: tls, fix WARNIING in __sk_msg_free

On Wed, 10 Jan 2024 14:01:23 -0800 John Fastabend wrote:
> A splice with MSG_SPLICE_PAGES will cause tls code to use the
> tls_sw_sendmsg_splice path in the TLS sendmsg code to move the user
> provided pages from the msg into the msg_pl. This will loop over the
> msg until msg_pl is full, checked by sk_msg_full(msg_pl). The user
> can also set the MORE flag to hint stack to delay sending until receiving
> more pages and ideally a full buffer.
> 
> If the user adds more pages to the msg than can fit in the msg_pl
> scatterlist (MAX_MSG_FRAGS) we should ignore the MORE flag and send
> the buffer anyways.
> 
> What actually happens though is we abort the msg to msg_pl scatterlist
> setup and then because we forget to set 'full record' indicating we
> can no longer consume data without a send we fallthrough to the 'continue'
> path which will check if msg_data_left(msg) has more bytes to send and
> then attempts to fit them in the already full msg_pl. Then next
> iteration of sender doing send will encounter a full msg_pl and throw
> the warning in the syzbot report.
> 
> To fix simply check if we have a full_record in splice code path and
> if not send the msg regardless of MORE flag.

Reviewed-by: Jakub Kicinski <kuba@...nel.org>