From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD220C83F17 for ; Mon, 28 Jul 2025 15:26:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4FCDE6B009A; Mon, 28 Jul 2025 11:26:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4D41B6B009B; Mon, 28 Jul 2025 11:26:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4111C6B009C; Mon, 28 Jul 2025 11:26:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 32A486B009A for ; Mon, 28 Jul 2025 11:26:16 -0400 (EDT) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id BE080586F5 for ; Mon, 28 Jul 2025 15:26:15 +0000 (UTC) X-FDA: 83714049510.08.2952490 Received: from mail-ed1-f43.google.com (mail-ed1-f43.google.com [209.85.208.43]) by imf01.hostedemail.com (Postfix) with ESMTP id 9C8BF40006 for ; Mon, 28 Jul 2025 15:26:13 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=jBPuZWAR; spf=pass (imf01.hostedemail.com: domain of jannh@google.com designates 209.85.208.43 as permitted sender) smtp.mailfrom=jannh@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1753716373; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ZqOC4wRRGhe0Mg49hUc2tJcMbQEAuNNfAJDotAhUq+A=; b=TOabZe97qb/4zdLHlW2g31NvIRAYj0DCJy36RSYNCU6oV0Ynci4effQrn898r5rld+5kJQ nERequccU3wQvlK0QtbCJjE/egf0Vx7BmHH0jG3XrE4hb0gAeFltF5+olsnWJf/c2rK13D Youk16NSB6VUDIxu+7g67evcCaqZnek= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=jBPuZWAR; spf=pass (imf01.hostedemail.com: domain of jannh@google.com designates 209.85.208.43 as permitted sender) smtp.mailfrom=jannh@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1753716373; a=rsa-sha256; cv=none; b=eNFE8WXqJmKyJPpMLUbHPFb2txpUQoy29G/4nD/YPK5sbB++3YkbezrAmTwuNjMaIWT42N 5T/0N9aI06a5MvOFRwbNRacCwuUTAKxl4nu/vBSCfkgX2AR86c2Rbesnl4I3KSXKvc2bez 2VVzvWlDpewM4XpekzjVfcNWR+cyZ9w= Received: by mail-ed1-f43.google.com with SMTP id 4fb4d7f45d1cf-6154c7b3ee7so9683a12.0 for ; Mon, 28 Jul 2025 08:26:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753716372; x=1754321172; darn=kvack.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=ZqOC4wRRGhe0Mg49hUc2tJcMbQEAuNNfAJDotAhUq+A=; b=jBPuZWARm2rnrC9z6HHkAXc9mUPNh0xWfZRNZy85ixptEnFvJqZSMEdInBTxBsRGpy 8UDlUFmb1XhYwtkTPWqJs8ar5G11R2uSKg2wzfi7LPj8JH0w/rzgBSds7SPQRSbkkZxV If3v1+vWZgdqoTKYdGMDGDVA6vopodGKYi9ofdbQBE28RwqMJNW3UISmFTDVnm2aedXK gqobs2hWqCNjcIEh5/69TM7jFhOzF8eDwU0L+kuzul3JByfYdpVssA8X6vNTgYXYGTtp YA3SX7FWFWJeF6KYgUev4hWBRbSau3vXTqV//jRfxk5FSzfe5W39ZJ6RV1RetZBxT6ah rFsA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753716372; x=1754321172; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=ZqOC4wRRGhe0Mg49hUc2tJcMbQEAuNNfAJDotAhUq+A=; b=qPd/thrAX8vkcS4YaLiknfXLeT3ffjjedjEEdLRyIFAEpr57/RZaO5w4jKUslyNjFq lfrumpyOju3G3e+brq46CePwWDm4r0ZamJ81AqpS0XS27n+DWMbVb1zCl/uTwPaHKTKi YUvSD6gKboofXJNPR+Yk1TNB7CiB3BXRz1IqpPhxqfo8JJOQrpQdvyXvB1o9nR0lIGmR XT9Hjf2jMaTBA4VqII1M3ut9beh6tyApi9pHNwrPNwv2a89r7MsJr/tHVJIsTNCPrZ02 inUXqF76o/17b9oQsLctArJIZ+Ls5QKnIgdX17hfrIqZDrxDFP0t7G5ImyZv18VpUGnB G53Q== X-Forwarded-Encrypted: i=1; AJvYcCXoSAupRNdppWdmV/0+VdXg5EIDL6V6Jr1I3UVz3PmuSkHkRqndGXQSOZntbgEoPk2swkPgGy9J1Q==@kvack.org X-Gm-Message-State: AOJu0YwFDVjYhYFG66GiZco/F9Kyz7gTOK8l9PZ53oHSCON0ItxzS14C wwSSaQ5CGpSbCBzBe2QrtE1JPItK5O4Okp09gARwGzcMwLkkI9FEXjhqQDEmlkGl6/YieSnRGM9 DtFZGnMO9p/s5d7ep/Fflgcnu+4wgCiJ2PuCtvRrv X-Gm-Gg: ASbGnctKln6s9XeeCu5JVErJ6278FX3dqeYrDhja9GLMB8Rmg8yd+igLiWFmdJzVad8 y32/+qdesCBAPG1ADpAtGbvP30wNxjoVIrLf1VMj5NTI2KGW59tF1VneCHpaQYDjdqlAOZ5fnX1 s//0LakOKi/XAlA9F0LjxgL7ZOYc77+4l4WZcheFcpm3jxysqEBPSkLdX9G/ceErzETb+5y1lHN JBEsA3AvMfk36Bgf/1nvbFSPDEvwPvltpU+JjgQKDa6 X-Google-Smtp-Source: AGHT+IFCoTgiMkG4zyb1dN1lLjGmK+W5Z95dZzG2OqP6BB8BASV/3pO2SP7BdCCxF+tbZ9PLcM55cUpWngS2TlYW05k= X-Received: by 2002:a05:6402:1a39:b0:615:2899:a4e5 with SMTP id 4fb4d7f45d1cf-6152899a78emr101033a12.5.1753716371615; Mon, 28 Jul 2025 08:26:11 -0700 (PDT) MIME-Version: 1.0 References: <20250723-kasan-tsbrcu-noquarantine-v1-1-846c8645976c@google.com> In-Reply-To: From: Jann Horn Date: Mon, 28 Jul 2025 17:25:35 +0200 X-Gm-Features: Ac12FXzgMg6AU9sijci9qK5lKdc5wEfC84NjWQbqd2yCO609j_hdZiglhUudTRA Message-ID: Subject: Re: [PATCH] kasan: skip quarantine if object is still accessible under RCU To: Andrey Konovalov Cc: Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , Vincenzo Frascino , Andrew Morton , Vlastimil Babka , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: p576t51u9rgo3bcck5khcnk3ayw5fjeb X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 9C8BF40006 X-Rspam-User: X-HE-Tag: 1753716373-882093 X-HE-Meta: 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 n5djUpdz lVZUEFewb9O6wgaPZLe6Awf8kblJxa2qG/LqRKDO3EFat5SnvmGU0W/0QpTguOR2wn7zQ+fZcTUop46M4PYQU9TRyo/yjPDtPTROE+7f7AqJ8nzvC1FeQMKkNoiO+m7xKJbPJ2o5lK1aX5n/r2yl258Rvn5Np7WDJKg+SL5DMpBB8OHUmkxX7wqxbj7v57uPGF4xs78ju93s5JDGZCSx1nXA0U9KRUSfkxmlm/cjEhjQhpSZCdTi3Smd2688SYk1VOBqNbYC749c3oeTZaWbySfZ5pGh5SCMeolgyUIKx19Fg3/zD3u/VbO76AQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Jul 27, 2025 at 12:06=E2=80=AFAM Andrey Konovalov wrote: > On Wed, Jul 23, 2025 at 4:59=E2=80=AFPM Jann Horn wrot= e: > > > > Currently, enabling KASAN masks bugs where a lockless lookup path gets = a > > pointer to a SLAB_TYPESAFE_BY_RCU object that might concurrently be > > recycled and is insufficiently careful about handling recycled objects: > > KASAN puts freed objects in SLAB_TYPESAFE_BY_RCU slabs onto its quarant= ine > > queues, even when it can't actually detect UAF in these objects, and th= e > > quarantine prevents fast recycling. > > > > When I introduced CONFIG_SLUB_RCU_DEBUG, my intention was that enabling > > CONFIG_SLUB_RCU_DEBUG should cause KASAN to mark such objects as freed > > after an RCU grace period and put them on the quarantine, while disabli= ng > > CONFIG_SLUB_RCU_DEBUG should allow such objects to be reused immediatel= y; > > but that hasn't actually been working. > > > > I discovered such a UAF bug involving SLAB_TYPESAFE_BY_RCU yesterday; I > > could only trigger this bug in a KASAN build by disabling > > CONFIG_SLUB_RCU_DEBUG and applying this patch. > > > > Signed-off-by: Jann Horn > > --- > > mm/kasan/common.c | 25 ++++++++++++++++++------- > > 1 file changed, 18 insertions(+), 7 deletions(-) > > > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > > index ed4873e18c75..9142964ab9c9 100644 > > --- a/mm/kasan/common.c > > +++ b/mm/kasan/common.c > > @@ -230,16 +230,12 @@ static bool check_slab_allocation(struct kmem_cac= he *cache, void *object, > > } > > > > static inline void poison_slab_object(struct kmem_cache *cache, void *= object, > > - bool init, bool still_accessible) > > + bool init) > > { > > void *tagged_object =3D object; > > > > object =3D kasan_reset_tag(object); > > > > - /* RCU slabs could be legally used after free within the RCU pe= riod. */ > > - if (unlikely(still_accessible)) > > - return; > > - > > kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE= _SIZE), > > KASAN_SLAB_FREE, init); > > > > @@ -261,7 +257,22 @@ bool __kasan_slab_free(struct kmem_cache *cache, v= oid *object, bool init, > > if (!kasan_arch_is_ready() || is_kfence_address(object)) > > return false; > > > > - poison_slab_object(cache, object, init, still_accessible); > > + /* > > + * If this point is reached with an object that must still be > > + * accessible under RCU, we can't poison it; in that case, also= skip the > > + * quarantine. This should mostly only happen when CONFIG_SLUB_= RCU_DEBUG > > + * has been disabled manually. > > + * > > + * Putting the object on the quarantine wouldn't help catch UAF= s (since > > + * we can't poison it here), and it would mask bugs caused by > > + * SLAB_TYPESAFE_BY_RCU users not being careful enough about ob= ject > > + * reuse; so overall, putting the object into the quarantine he= re would > > + * be counterproductive. > > + */ > > + if (still_accessible) > > + return false; > > + > > + poison_slab_object(cache, object, init); > > > > /* > > * If the object is put into quarantine, do not let slab put th= e object > > @@ -519,7 +530,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsig= ned long ip) > > if (check_slab_allocation(slab->slab_cache, ptr, ip)) > > return false; > > > > - poison_slab_object(slab->slab_cache, ptr, false, false); > > + poison_slab_object(slab->slab_cache, ptr, false); > > return true; > > } > > > > > > --- > > base-commit: 89be9a83ccf1f88522317ce02f854f30d6115c41 > > change-id: 20250723-kasan-tsbrcu-noquarantine-e207bb990e24 > > > > -- > > Jann Horn > > > > Acked-by: Andrey Konovalov Thanks! > Would it be hard to add KUnit test to check that KASAN detects such issue= s? Sent a separate patch with a kunit test.