netdev - Re: [syzbot] [crypto?] general protection fault in cryptd_hash

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Message-ID: <1521347.1686744278@warthog.procyon.org.uk>
Date: Wed, 14 Jun 2023 13:04:38 +0100
From: David Howells <dhowells@...hat.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: dhowells@...hat.com,
    syzbot <syzbot+e79818f5c12416aba9de@...kaller.appspotmail.com>,
    davem@...emloft.net, linux-crypto@...r.kernel.org,
    linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
    pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [crypto?] general protection fault in cryptd_hash_export

Herbert Xu <herbert@...dor.apana.org.au> wrote:

> David, the logic for calling hash_alloc_result looks quite different
> from that on whether you do the hash finalisation.  I'd suggest that
> you change them to use the same check, and also set use NULL instead
> of ctx->result if you didn't call hash_alloc_result.

I don't fully understand what the upstream hash_sendmsg() is doing.  Take this
bit for example:

	if (!ctx->more) {
		if ((msg->msg_flags & MSG_MORE))
			hash_free_result(sk, ctx);

Why is it freeing the old result only if MSG_MORE is now set, but wasn't set
on the last sendmsg()?

David