From: Andy Lutomirski Subject: Re: [PATCH V2] Fix a sleep-in-atomic bug in shash_setkey_unaligned Date: Mon, 2 Oct 2017 21:18:24 -0700 Message-ID: References: <1506997522-26684-1-git-send-email-baijiaju1990@163.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: "David S. Miller" , Herbert Xu , Neil Horman , vyasevich@gmail.com, Andrew Lutomirski , Kalle Valo , Linux Crypto Mailing List , Network Development , linux-sctp@vger.kernel.org, Linux Wireless List To: Jia-Ju Bai Return-path: Received: from mail.kernel.org ([198.145.29.99]:41194 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750767AbdJCESq (ORCPT ); Tue, 3 Oct 2017 00:18:46 -0400 Received: from mail-it0-f43.google.com (mail-it0-f43.google.com [209.85.214.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F3B7C218C9 for ; Tue, 3 Oct 2017 04:18:45 +0000 (UTC) Received: by mail-it0-f43.google.com with SMTP id 85so10108881ith.2 for ; Mon, 02 Oct 2017 21:18:45 -0700 (PDT) In-Reply-To: <1506997522-26684-1-git-send-email-baijiaju1990@163.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: > On Oct 2, 2017, at 7:25 PM, Jia-Ju Bai wrote: > > The SCTP program may sleep under a spinlock, and the function call path is: > sctp_generate_t3_rtx_event (acquire the spinlock) > sctp_do_sm > sctp_side_effects > sctp_cmd_interpreter > sctp_make_init_ack > sctp_pack_cookie > crypto_shash_setkey > shash_setkey_unaligned > kmalloc(GFP_KERNEL) > I'm going to go out on a limb here: why on Earth is out crypto API so full of indirection that we allocate memory at all here? We're synchronously computing a hash of a small amount of data using either HMAC-SHA1 or HMAC-SHA256 (determined at runtime) if I read it right. There's a sane way to do this that doesn't need kmalloc, alloca, or fancy indirection. And then there's crypto_shash_xyz(). --Andy, who is sick of seeing stupid bugs caused by the fact that it's basically impossible to use the crypto API in a sane way. P.S. gnulib has: int hmac_sha256 (const void *key, size_t keylen, const void *in, size_t inlen, void *resbuf); An init/update/final-style API would be nice, but something like this would be a phenomenal improvement over what we have.