From nobody Sat Feb 7 17:24:55 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F318EC873F for ; Thu, 7 Sep 2023 16:09:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237652AbjIGQJL convert rfc822-to-8bit (ORCPT ); Thu, 7 Sep 2023 12:09:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46722 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241692AbjIGQIa (ORCPT ); Thu, 7 Sep 2023 12:08:30 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BC91F2729 for ; Thu, 7 Sep 2023 09:02:25 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-251-8f0ph68FMmGbI3MMsr5Spg-1; Thu, 07 Sep 2023 13:42:24 +0100 X-MC-Unique: 8f0ph68FMmGbI3MMsr5Spg-1 Received: from AcuMS.Aculab.com (10.202.163.4) by AcuMS.aculab.com (10.202.163.4) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Thu, 7 Sep 2023 13:42:20 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Thu, 7 Sep 2023 13:42:20 +0100 From: David Laight To: 'Vlastimil Babka' , "linux-kernel@vger.kernel.org" , "'linux-mm@kvack.org'" CC: 'Kees Cook' , 'Christoph Lameter' , 'Pekka Enberg' , 'David Rientjes' , 'Joonsoo Kim' , 'Andrew Morton' , 'Eric Dumazet' , "Hyeonggon Yoo" <42.hyeyoo@gmail.com>, Roman Gushchin Subject: Subject: [PATCH v2] slab: kmalloc_size_roundup() must not return 0 for non-zero size Thread-Topic: Subject: [PATCH v2] slab: kmalloc_size_roundup() must not return 0 for non-zero size Thread-Index: Adnhh8rbtLpHk7QBQE+HpPR0NWDZ5g== Date: Thu, 7 Sep 2023 12:42:20 +0000 Message-ID: <4d31a2bf7eb544749023cf491c0eccc8@AcuMS.aculab.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The typical use of kmalloc_size_roundup() is: ptr =3D kmalloc(sz =3D kmalloc_size_roundup(size), ...); if (!ptr) return -ENOMEM. This means it is vitally important that the returned value isn't less than the argument even if the argument is insane. In particular if kmalloc_slab() fails or the value is above (MAX_ULONG - PAGE_SIZE) zero is returned and kmalloc() will return it's single zero-length buffer. Fix by returning the input size on error or if the size exceeds a 'sanity' limit. kmalloc() will then return NULL is the size really is too big. Signed-off-by: David Laight Fixes: 05a940656e1eb ("slab: Introduce kmalloc_size_roundup()") Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> --- v2: - Use KMALLOC_MAX_SIZE for upper limit. (KMALLOC_MAX_SIZE + 1 may give better code on some archs!) - Invert test for overlarge for consistency. - Put a likely() on result of kmalloc_slab(). mm/slab_common.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/mm/slab_common.c b/mm/slab_common.c index cd71f9581e67..0fb7c7e19bad 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -747,22 +747,22 @@ size_t kmalloc_size_roundup(size_t size) { struct kmem_cache *c; =20 - /* Short-circuit the 0 size case. */ - if (unlikely(size =3D=3D 0)) - return 0; - /* Short-circuit saturated "too-large" case. */ - if (unlikely(size =3D=3D SIZE_MAX)) - return SIZE_MAX; + if (size && size <=3D KMALLOC_MAX_CACHE_SIZE) { + /* + * The flags don't matter since size_index is common to all. + * Neither does the caller for just getting ->object_size. + */ + c =3D kmalloc_slab(size, GFP_KERNEL, 0); + return likely(c) ? c->object_size : size; + } + /* Above the smaller buckets, size is a multiple of page size. */ - if (size > KMALLOC_MAX_CACHE_SIZE) + if (size && size <=3D KMALLOC_MAX_SIZE) return PAGE_SIZE << get_order(size); =20 - /* - * The flags don't matter since size_index is common to all. - * Neither does the caller for just getting ->object_size. - */ - c =3D kmalloc_slab(size, GFP_KERNEL, 0); - return c ? c->object_size : 0; + /* Return 'size' for 0 and very large - kmalloc() may fail. */ + return size; + } EXPORT_SYMBOL(kmalloc_size_roundup); =20 --=20 2.17.1 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)