netdev - RE: [PATCH net v2] net/tls: fix sk_msg trim on fallback to copy mode

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Message-ID: <5dc18ba56aec_48332abec96485b835@john-XPS-13-9370.notmuch>
Date:   Tue, 05 Nov 2019 06:48:05 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        borisp@...lanox.com, aviadye@...lanox.com,
        john.fastabend@...il.com, daniel@...earbox.net,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        syzbot+f8495bff23a879a6d0bd@...kaller.appspotmail.com,
        syzbot+6f50c99e8f6194bf363f@...kaller.appspotmail.com,
        Eric Biggers <ebiggers@...nel.org>,
        herbert@...dor.apana.org.au, glider@...gle.com,
        linux-crypto@...r.kernel.org
Subject: RE: [PATCH net v2] net/tls: fix sk_msg trim on fallback to copy mode

Jakub Kicinski wrote:
> sk_msg_trim() tries to only update curr pointer if it falls into
> the trimmed region. The logic, however, does not take into the
> account pointer wrapping that sk_msg_iter_var_prev() does nor
> (as John points out) the fact that msg->sg is a ring buffer.
> 
> This means that when the message was trimmed completely, the new
> curr pointer would have the value of MAX_MSG_FRAGS - 1, which is
> neither smaller than any other value, nor would it actually be
> correct.
> 
> Special case the trimming to 0 length a little bit and rework
> the comparison between curr and end to take into account wrapping.
> 
> This bug caused the TLS code to not copy all of the message, if
> zero copy filled in fewer sg entries than memcopy would need.
> 
> Big thanks to Alexander Potapenko for the non-KMSAN reproducer.
> 
> v2:
>  - take into account that msg->sg is a ring buffer (John).
> 
> Link: https://lore.kernel.org/netdev/20191030160542.30295-1-jakub.kicinski@netronome.com/ (v1)
> 
> Fixes: d829e9c4112b ("tls: convert to generic sk_msg interface")
> Reported-by: syzbot+f8495bff23a879a6d0bd@...kaller.appspotmail.com
> Reported-by: syzbot+6f50c99e8f6194bf363f@...kaller.appspotmail.com
> Co-developed-by: John Fastabend <john.fastabend@...il.com>
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> ---
> CC: Eric Biggers <ebiggers@...nel.org>
> CC: herbert@...dor.apana.org.au
> CC: glider@...gle.com
> CC: linux-crypto@...r.kernel.org
> ---

I'll run it through our CI here when I get a chance but LGTM
thanks for sending this and tracking it down. Per process.rst
I guess we add Signed-off-by lines instead of acks from
co-developers. News to me.

Signed-off-by: John Fastabend <john.fastabend@...il.com>