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From:   Nick Bowler <nbowler@draconx.ca>
Date:   Mon, 27 Jul 2020 13:42:22 -0400
Message-ID: <CADyTPEx_dppsUK_SdPKfn-1ZgEzYubbe4tBmXSKBBXTFT5cbWA@mail.gmail.com>
Subject: Re: [PATCH] Re: PROBLEM: cryptsetup fails to unlock drive in 5.8-rc6 (regression)
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org
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On 2020-07-27, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Mon, Jul 27, 2020 at 05:05:54PM +0100, Al Viro wrote:
>> On Thu, Jul 23, 2020 at 11:51:01AM -0400, Nick Bowler wrote:
>> > After installing Linux 5.8-rc6, it seems cryptsetup can no longer
>> > open LUKS volumes.  Regardless of the entered passphrase (correct
>> > or otherwise), the result is a very unhelpful "Keyslot open failed."
>> > message.
[...]
> Oh, fuck...  Please see if the following fixes your reproducer; the braino
> is, of course, that instead of fetching ucmsg->cmsg_len into ucmlen we read
> the entire thing into cmsg.  Other uses of ucmlen had been replaced with
> cmsg.cmsg_len; this one was missed.
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> diff --git a/net/compat.c b/net/compat.c
> index 5e3041a2c37d..434838bef5f8 100644
> --- a/net/compat.c
> +++ b/net/compat.c
> @@ -202,7 +202,7 @@ int cmsghdr_from_user_compat_to_kern(struct msghdr
> *kmsg, struct sock *sk,
>
>  		/* Advance. */
>  		kcmsg = (struct cmsghdr *)((char *)kcmsg + tmp);
> -		ucmsg = cmsg_compat_nxthdr(kmsg, ucmsg, ucmlen);
> +		ucmsg = cmsg_compat_nxthdr(kmsg, ucmsg, cmsg.cmsg_len);
>  	}
>
>  	/*

This patch appears to resolve the problem when applied on top of 5.8-rc7.

Thanks,
  Nick