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 59191606A31A for ; Tue, 27 Oct 2026 14:41:50 +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=F/aE3Kg9 Received: by kanga.kvack.org (Postfix) id 685F76B0791; Tue, 27 Oct 2026 10:41:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 636E36B0793; Tue, 27 Oct 2026 10:41:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 527C56B0794; Tue, 27 Oct 2026 10:41:49 -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 28A2B6B0791 for ; Tue, 27 Oct 2026 10:41:49 -0400 (EDT) Received: from smtpin30.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id A06341A05D8 for ; Tue, 27 Oct 2026 14:41:48 +0000 (UTC) X-FDA: 85368670296.30.A624D72 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf08.hostedemail.com (Postfix) with ESMTP id E5253160009 for ; Tue, 27 Oct 2026 14:41:46 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="F/aE3Kg9"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf08.hostedemail.com: domain of pratyush@kernel.org designates 172.234.252.31 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=1793112107; 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=Cxbcd97TigLbOc2nsbdYTtwGKr7cyQITuDlutqpOwp0=; b=KAAtj/4DQDFXRi/OzDhhTEby+d+t5nNf59O+NLnAM2aG7bmqXcCWQ2kzfmh3ZCCz6z3GIo KeqDHjEvm+02wJQwCp+F7ABw0OLtbcr/Evmy8Bh3tQ+XXqENy5XGOlNLe+gXhM1jiW1TAo +fQOiR/Kf9K4n8OV/gt9zqAKwmWUAEI= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="F/aE3Kg9"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf08.hostedemail.com: domain of pratyush@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=pratyush@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793112107; b=HRBU+G3X3bids4MVzgNianBtVEIGTZqc+46T9kpTq5ns7rEAi6IOZiSNSwPKaRotbAb/OL lfc7lpFIvcDfUipG14eWiPTLQXcXaRbC0d8Mz3FkJl+3uTfNtD7tsuCUt3Z8MgZnjkfQJc 7/XgqOfHhYfPbYOzw8heG3mdb/1IKwo= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 1495641A3F; Tue, 27 Oct 2026 14:41:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61A8B1F01825; Tue, 27 Oct 2026 14:41:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793112105; bh=Cxbcd97TigLbOc2nsbdYTtwGKr7cyQITuDlutqpOwp0=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=F/aE3Kg94sj9fXVFeMOGEhnFPh7IPM73CFA/LmgAAZfItP5Nw7PY1j3LmhUrie3RF WWOkZE/CrqgRjQtrY5czn2Xyhnu7Jhr5cpxZIRN6ucwFL7953eyR9cc+xJIfYeqrtx x427FQ040+6sFoWm3ZQYEETyJqIrMT+OQrZXuAnXJaqqyPl1iBQjI9L2UIFGYkQFmj rXT+tzW5xd2XQNYXVDL7CnDknr0SBZMXfP2tLX56GVF5sYE25tWUnjur3LSUQsNAM/ e9FZ57Wpnn2LjlHGFOu9V+hCx07zuXfQscJu7g4AtCiXI1sCKypZwCMKvsYpJoK5pk vtVZ2ljYGxZvA== 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 03/46] mm/memfd: check for real shmem inodes before accessing shmem state In-Reply-To: <20261027-fixes_core-v1-3-6f74bec9a5bb@kernel.org> (David Hildenbrand's message of "Tue, 27 Oct 2026 00:17:23 +0100") References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-3-6f74bec9a5bb@kernel.org> Date: Tue, 27 Oct 2026 15:41:34 +0100 Message-ID: <2vxzh5i7p5nl.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: E5253160009 X-Stat-Signature: pxmja9nk3nk13yntmc7oqnx5se65txz3 X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-17.6 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=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793112106-593856 X-HE-Meta: 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 YZGDW/SC NWOxVJAPueFx74kea2X0+xscFofQmRyLUDfOC4f/gO8r/ggRZh2Eqtuzm9eW06RjpJw6GIsZHiNP7s7J+mw31pIoTtwhYSyFCZY1YovqG6bZ6hmPufw03imDOjJJX7DaUxY4fHATfs6OoPlhQssdDncjpsP1mjunyuBcECxrmi9Qn2XildwYUauER6teJSyXam7YIPwvDJNA4PijKchHmJQOAzRUlNCadWr/Y5+CMm9ny5R6jwkIrYydWZjGqOp+zxlHj9F2fay0y7FlyV6eZocZQOnlTVxMYlvxEywGvahjsV0T41BYbgjqJaQ== 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 Tue, Oct 27 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. 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. 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(). 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. > > 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 > Signed-off-by: David Hildenbrand (Arm) > --- > 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(-) > > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h > index a7c7a96a7cbf9..2ceca7993e4f5 100644 > --- a/include/linux/shmem_fs.h > +++ b/include/linux/shmem_fs.h > @@ -117,8 +117,14 @@ extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr, > unsigned long len, unsigned long pgoff, unsigned long flags); > extern int shmem_lock(struct file *file, int lock, struct ucounts *ucounts); > #ifdef CONFIG_SHMEM > +bool file_inode_is_shmem(const struct inode *inode); > bool shmem_mapping(const struct address_space *mapping); > #else > +static inline bool file_inode_is_shmem(const struct inode *inode) > +{ > + return false; > +} > + > static inline bool shmem_mapping(const struct address_space *mapping) > { > return false; > diff --git a/mm/memfd.c b/mm/memfd.c > index 0f6fff004f5e4..7d2da23157003 100644 > --- a/mm/memfd.c > +++ b/mm/memfd.c > @@ -211,12 +211,14 @@ static int memfd_wait_for_pins(struct address_space *mapping) > > static unsigned int *memfd_file_seals_ptr(struct file *file) > { > - if (shmem_file(file)) > - return &SHMEM_I(file_inode(file))->seals; > + struct inode *inode = file_inode(file); > + > + if (file_inode_is_shmem(inode)) > + return &SHMEM_I(inode)->seals; > > #ifdef CONFIG_HUGETLBFS > if (is_file_hugepages(file)) > - return &HUGETLBFS_I(file_inode(file))->seals; > + return &HUGETLBFS_I(inode)->seals; > #endif > > return NULL; > diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c > index 59de210bee5f9..c0811407ce397 100644 > --- a/mm/memfd_luo.c > +++ b/mm/memfd_luo.c > @@ -582,7 +582,7 @@ static bool memfd_luo_can_preserve(struct liveupdate_file_handler *handler, > { > struct inode *inode = file_inode(file); > > - return shmem_file(file) && !inode->i_nlink; > + return file_inode_is_shmem(inode) && !inode->i_nlink; > } > > static unsigned long memfd_luo_get_id(struct file *file) > diff --git a/mm/shmem.c b/mm/shmem.c > index fadf23f9e21ed..0d41aac125df9 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -275,6 +275,11 @@ static const struct vm_operations_struct shmem_vm_ops; > static const struct vm_operations_struct shmem_anon_vm_ops; > static struct file_system_type shmem_fs_type; > > +bool file_inode_is_shmem(const struct inode *inode) > +{ > + return inode->i_fop == &shmem_file_operations; > +} > + > bool shmem_mapping(const struct address_space *mapping) > { > return mapping->a_ops == &shmem_aops; -- Regards, Pratyush Yadav