Re: [PATCH net] net/tls: fix sk_msg trim on fallback to copy mode

[Jakub Kicinski <jakub.kicinski@netronome.com>]

On Wed, 30 Oct 2019 09:05:42 -0700, 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.
> 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.
> 
> 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.
> 
> Fixes: d829e9c4112b ("tls: convert to generic sk_msg interface")
> Reported-by: syzbot+f8495bff23a879a6d0bd@syzkaller.appspotmail.com
> Reported-by: syzbot+6f50c99e8f6194bf363f@syzkaller.appspotmail.com
> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> ---
> Daniel, John, does this look okay?
> 
> CC: Eric Biggers <ebiggers@kernel.org>
> CC: herbert@gondor.apana.org.au
> CC: glider@google.com
> CC: linux-crypto@vger.kernel.org
> 
>  net/core/skmsg.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Daniel, John does this patch look reasonable? I must admit 
the skmsg stuff in TLS scares me, it'd appreciate an ack.