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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4CA2DD0D172 for ; Wed, 7 Jan 2026 20:28:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9CA526B0088; Wed, 7 Jan 2026 15:28:31 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 974C16B0093; Wed, 7 Jan 2026 15:28:31 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 880FA6B0095; Wed, 7 Jan 2026 15:28:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 74F6C6B0088 for ; Wed, 7 Jan 2026 15:28:31 -0500 (EST) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 18AEBC1F6C for ; Wed, 7 Jan 2026 20:28:31 +0000 (UTC) X-FDA: 84306305622.08.BDB2780 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf04.hostedemail.com (Postfix) with ESMTP id 7235D40012 for ; Wed, 7 Jan 2026 20:28:29 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=E5IRqCmm; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf04.hostedemail.com: domain of kees@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=kees@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1767817709; a=rsa-sha256; cv=none; b=2WXmsKgibztKbrsqBvs0siRWfGgCeTskmciEFEgdsqKLQ2BCyviX3UykeOYT48RdO7zNaU 4JuyD1Jhl9AermOFvJj14y/ejUyOtITFdW2CrGiWbqeLMyyXRJqYP1cMID3cI0buFR9G1K Ad0AdXXUjpaySpIQmCBZP8/XDgwKY3Y= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=E5IRqCmm; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf04.hostedemail.com: domain of kees@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=kees@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1767817709; 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=E1HLKRJudO06EHz5daCWcSK6ZEDuvgp2UnlllgnfcWY=; b=P4PrHv9ZYVTx1/VmfgYQnFdFuUA8TpBgXyJMDRxy8mY8SJl8CaeBPx2TJnM7weACrau+SX 983ZtZOzxbvFO9Iq7TJqKK+1JXQfXEqlK40LQA/cBdfnpJ8/p6VhK35UZPIASx2pAGSJp4 ExrlpULRTeUPzx14k9vtTNgUYKwc4K8= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 88AE56000A; Wed, 7 Jan 2026 20:28:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3867EC4CEF1; Wed, 7 Jan 2026 20:28:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767817708; bh=H7h/gH0TCzCbiszMKAa3EWkIHJGcdsYIdjeIZkzHok8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=E5IRqCmm+zy5R+XgK8ZDidOJvdt3UHkdCGBAOeL7OnfRhmgaxSFlYefWNz5osV8KR y6vx7e4wmpU3GBzVgqEckzKbW3yQTl7KI1iQ7c4JF4FnZA/OX9EWGoZn49qoXw+0kO IuecKJX3QYQ4gLPWcI+oe+Q3c0F1y9KBvxGpkHGeI19PDbruice6ImZI8UIvQg5VUG DXOvh3n/Adxu9c14RNXnKZ5jrLcqy/w5X4Ewhhqi1Zfmw9BcjNwyF8lcsX9ccMucT9 jFKvmYwcApNLjX3WrRzUTE2DyjsK422/mkXgBUPTr7uAkmG37vpP/39W+Qf405NjlK 747IyRkjWg8TA== Date: Wed, 7 Jan 2026 12:28:27 -0800 From: Kees Cook To: Maciej =?utf-8?Q?=C5=BBenczykowski?= Cc: Maciej Wieczor-Retman , joonki.min@samsung-slsi.corp-partner.google.com, Andrew Morton , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Marco Elver , Andrew Morton , Uladzislau Rezki , Danilo Krummrich , jiayuan.chen@linux.dev, syzbot+997752115a851cb0cf36@syzkaller.appspotmail.com, Maciej Wieczor-Retman , kasan-dev@googlegroups.com, Kernel hackers , linux-mm@kvack.org Subject: Re: KASAN vs realloc Message-ID: <202601071226.8DF7C63@keescook> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 7235D40012 X-Stat-Signature: grhm6qqxqen5e1sgoufx5z7f1fxzitgr X-Rspam-User: X-HE-Tag: 1767817709-995872 X-HE-Meta: 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 t/7uOHUy dS9bCWE/dprypwIyH4OIZpyWEg2V4pBPslt2AL/7Pi3UVXhtifBqqdiyeQGfyMi9m6r0WbW9fcZBKZU+5ZkS5F7JDdWr6pAfl0MR9H8Z80wWSv6HmeOEmfUWAKnCn7xaOn/WoIZO43nLfYG5dCXUuspQq2vcgi/47MuEQaUSoGjs8Gfi2CBCi4m8bFyWOMt7EfNUuCfyAzvcuXLEvbgrD7RDC3Mx6ZhyluvK+5KaWKBY6DAoWJ93WwHPCwzlQeYCL+yO1q2up8Mj6PtBDfU8/98ACIMjS+NG/Z94gILee22TRXSfxPYc8KRG+SMsk4LYdh1XLWTN+XdvXgSISu07gzZxFvC9N1YDLXd4nGyZOqj5uKSl9vX1SxhY2RUeI2d+j83O39wVpe6K0X+u/3C7sKVnLK61wDjuJ03Raqs2b/kvKP+E= 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 Tue, Jan 06, 2026 at 01:42:45PM +0100, Maciej Żenczykowski wrote: > We've got internal reports (b/467571011 - from CC'ed Samsung > developer) that kasan realloc is broken for sizes that are not a > multiple of the granule. This appears to be triggered during Android > bootup by some ebpf program loading operations (a struct is 88 bytes > in size, which is a multiple of 8, but not 16, which is the granule > size). > > (this is on 6.18 with > https://lore.kernel.org/all/38dece0a4074c43e48150d1e242f8242c73bf1a5.1764874575.git.m.wieczorretman@pm.me/ > already included) > > joonki.min@samsung-slsi.corp-partner.google.com summarized it as > "When newly requested size is not bigger than allocated size and old > size was not 16 byte aligned, it failed to unpoison extended area." > > and *very* rough comment: > > Right. "size - old_size" is not guaranteed 16-byte alignment in this case. > > I think we may unpoison 16-byte alignment size, but it allowed more > than requested :( > > I'm not sure that's right approach. > > if (size <= alloced_size) { > - kasan_unpoison_vmalloc(p + old_size, size - old_size, > + kasan_unpoison_vmalloc(p + old_size, round_up(size - > old_size, KASAN_GRANULE_SIZE), > KASAN_VMALLOC_PROT_NORMAL | > KASAN_VMALLOC_VM_ALLOC | > KASAN_VMALLOC_KEEP_TAG); > /* > * No need to zero memory here, as unused memory will have > * already been zeroed at initial allocation time or during > * realloc shrink time. > */ > - vm->requested_size = size; > + vm->requested_size = round_up(size, KASAN_GRANULE_SIZE); > > my personal guess is that > > But just above the code you quoted in mm/vmalloc.c I see: > if (size <= old_size) { > ... > kasan_poison_vmalloc(p + size, old_size - size); > > is also likely wrong?? Considering: > > mm/kasan/shadow.c > > void __kasan_poison_vmalloc(const void *start, unsigned long size) > { > if (!is_vmalloc_or_module_addr(start)) > return; > > size = round_up(size, KASAN_GRANULE_SIZE); > kasan_poison(start, size, KASAN_VMALLOC_INVALID, false); > } > > This doesn't look right - if start isn't a multiple of the granule. I don't think we can ever have the start not be a granule multiple, can we? I'm not sure how any of this is supposed to be handled by KASAN, though. It does seem like a round_up() is missing, though? -Kees -- Kees Cook