From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C05A9606A324 for ; Fri, 30 Oct 2026 11:33:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=BHb4rT89 Received: by kanga.kvack.org (Postfix) id BEE636B00EF; Fri, 30 Oct 2026 07:33:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B9F436B05B1; Fri, 30 Oct 2026 07:33:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AB5B96B05B2; Fri, 30 Oct 2026 07:33:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 807E16B00EF for ; Fri, 30 Oct 2026 07:33:21 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 7AB248060B for ; Fri, 30 Oct 2026 11:33:20 +0000 (UTC) X-FDA: 85379081760.12.BA4BDF9 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf21.hostedemail.com (Postfix) with ESMTP id DB2B91C0004 for ; Fri, 30 Oct 2026 11:33:18 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=BHb4rT89; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf21.hostedemail.com: domain of pratyush@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=pratyush@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793359998; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=kc1nYy3NbBrATEnmu304kSXCIcQUyPU78cqEyUeTLQk=; b=Az0tb8r0TrLRdfqO+PpVCKqRoE3zFq2V5rLoep9Wr6IumTBYEtCAMB7QToogtvlGx9YH1z e36Wfn+3znkLK93hXgrNaNhDIpKGtEErJwhp+B8vwoIZ/R4Ykt/362xO4Nc3NGajd1H3a1 I3tI0qoAckSa7vdKZvx+qxKSvy2a1/U= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=BHb4rT89; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf21.hostedemail.com: domain of pratyush@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=pratyush@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793359998; b=iotTd4RXl8Rqta0z+ASU0A9k81hZ5cMzJCx8NwuHqrEVgA+aXSCzsPfU71GcDJpN94l8a3 wOv9ibWpDNodmfrQj1cx55Z6GR1FVw8Siv1+zz4u66GVDVsNNjH9DOvPjJVn4PPFfk4Li8 PpRUh1SrIz0MkORMHZP99KNrUTmiTP8= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 5EAF2601EE; Fri, 30 Oct 2026 11:33:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32A5A1F000C1; Fri, 30 Oct 2026 11:33:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793359998; bh=kc1nYy3NbBrATEnmu304kSXCIcQUyPU78cqEyUeTLQk=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=BHb4rT89dXjX/iZaObEefV3p90/w7FDU1AnmrNDjsWGet3bMCVuHxPhhh8maCSV/h zHFPhZNhQ+icw2cAAzLgVil3nTxqrp8v/shvpU7wgx9O2HOr6scmGto/DwnEx43YLR U8QuxRoob6poB0ebRlGoVLdYs4EXRG/OEIcmFg9nLjCoFcmkfPK+kLiNtyRR5jFfK/ kPdRH7C4xmDmfWvUUGNc6QJpyNgV5aZiZ4d9NVAt97UVbCogRFpjqWS63JZdadrQNq Et9wov2jU3Uf8UCr6K6rvisW1XibSsetO8Dm61vUCe5/c67aIiNMH6e+Dl8WkmU+fi vUl1VbxFRwh2Q== From: Pratyush Yadav To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Chris Mason Subject: Re: [PATCH v2 03/47] mm/memfd: check for real shmem inodes before accessing shmem state In-Reply-To: <20261029-fixes_core-v2-3-a64ce7f83abb@kernel.org> (David Hildenbrand's message of "Thu, 29 Oct 2026 21:32:58 +0100") References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> <20261029-fixes_core-v2-3-a64ce7f83abb@kernel.org> Date: Fri, 30 Oct 2026 12:33:06 +0100 Message-ID: <2vxzmrrvmnil.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: DB2B91C0004 X-Rspam-User: X-Stat-Signature: s5ng6u6tzmhjjwbnhqox88ordjqgq1xw X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1793359998-685042 X-HE-Meta: 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 6+72Acmn kjW24ESJZuZf0YnpTfS6KRqsCMOAWqpGyysjQtkdPeDH8W35NG4LeV3NnJ3camSDq/JiDQa4gIzRD68yZE934hH2F8RItB25zyXxP3NKCymDY9uAPdvy9ZkuQ2cdMsJUy3RFoxGoJAAWWsjAwapC1uDfV/gi/XnctdmqrOk/ZG1T3e8bSXp4ThiweNy0Ie+o30YGp5NzSkE/15WTLzHqtH53JdI86uY5lShvjqiQ6AhVatfgoQiYy2jnmrkf+f5NIb/bUQ9amC2kcKZMU2vKIACNLVJwGzLoQSl/oIvdgB/5+P8veojIisZUHhV4MBLSCrK7NfdBOzjQ1UQGPq9AeH2UgLCUSka5bLzSbspzg48CHjcw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi David, On Thu, Oct 29 2026, David Hildenbrand (Arm) wrote: > shmem_file() only checks a file's backing mapping. That mapping can belong > to another file, as with a Coda file backed by a tmpfs container after > mmap(). It does not establish that file_inode(file) is a shmem inode. > > Seal handling and memfd preservation use this check before accessing > shmem inode state, so they can access an inode of the wrong type. > > Add file_inode_is_shmem() to check the inode's file operations in both > paths. This identifies regular shmem inodes, including those used by > memfds and ordinary tmpfs files, independently of wrapper file operations. > > Fixes: c49fcfcda8b5 ("mm/shmem: update file sealing comments and file checking") > Fixes: b3749f174d68 ("mm: memfd_luo: allow preserving memfd") > Cc: stable@vger.kernel.org > Reported-by: Chris Mason > Reviewed-by: Rik van Riel > Reviewed-by: Mike Rapoport (Microsoft) > Signed-off-by: David Hildenbrand (Arm) Maybe you missed my email on v1 [0], so here's another try: Why not update shmem_file() to do this check instead? Having a shmem_file() that might not always return the right result on a file seems like a landmine. For example, you missed check_memfd_seals() in udmabuf or memfd_pin_folios() in gup. Both want to only look at "proper" shmem files, and should not do any work on a Coda file with a shmem mapping. Plus, someone later down the line might use shmem_file() without knowing this subtle problem, and we probably would miss it in review. For callers that only care about the mapping should then use shmem_mapping(). I am not sure if there are any. Perhaps that would be collapse_file()? But TBH I don't really understand khugepaged all that much. All other callers of shmem_file() seem to care about the actual inode. [0] https://lore.kernel.org/all/2vxzh5i7p5nl.fsf@kernel.org/ > --- > include/linux/shmem_fs.h | 6 ++++++ > mm/memfd.c | 8 +++++--- > mm/memfd_luo.c | 2 +- > mm/shmem.c | 5 +++++ > 4 files changed, 17 insertions(+), 4 deletions(-) [...] -- Regards, Pratyush Yadav