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 DE02C606A324 for ; Fri, 30 Oct 2026 12:30:05 +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=Fg02mM+P Received: by kanga.kvack.org (Postfix) id 0B4AA6B05B3; Fri, 30 Oct 2026 08:30:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 08D156B05B4; Fri, 30 Oct 2026 08:30:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EBDAB6B05B6; Fri, 30 Oct 2026 08:30:04 -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 C65626B05B3 for ; Fri, 30 Oct 2026 08:30:04 -0400 (EDT) Received: from smtpin11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id C64F7406AA for ; Fri, 30 Oct 2026 12:30:03 +0000 (UTC) X-FDA: 85379224686.11.F106866 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf26.hostedemail.com (Postfix) with ESMTP id 210FC14000B for ; Fri, 30 Oct 2026 12:30:01 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Fg02mM+P; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf26.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=1793363402; 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=hu2ezbFXEyhvzPYipLaNmuX98BEqOJW5J/R/m8RSLb0=; b=CS62BzH+qgq1P2ojVLH/NTM0fUz6XMEdlPttX7bEhHULRLbljY5/6UhRWe9T1VTlD5tHae wx3Ma0DC5Eat2yF/zU4dB/7MzHVOBvyzmwHiJQnn+N8lm0EgFVf2hBM2OeeNU2CXsnHh4t WdmaXHvlrya2+KRYdl6ElB7OjW4FElU= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Fg02mM+P; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf26.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=1793363402; b=WY2+jBBs6Cv6TRF62PsRtnHn+rJDrsFe2SB3RyDgEuAft1ghUyezTdv4x8mC41HUCjffCJ MR2CehYgRGbqeCDSa02AMMmqbkgp71/L+PioqgL1pi9OHDdKeMEy2n528kQ2QMFV0Nw7jz DgMJaglQx9Yodwd0GD8NDCfqyydQnic= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 94CE0605C6; Fri, 30 Oct 2026 12:30:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BAAFB1F0093A; Fri, 30 Oct 2026 12:29:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793363401; bh=hu2ezbFXEyhvzPYipLaNmuX98BEqOJW5J/R/m8RSLb0=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=Fg02mM+PuPWrmf4vwct0jXlFZMeQuDiAYwpOteG7E7NWa+rawXxJHLQ+rxU4Iu/5z dHaD/qCLNflG2BY/40J/PeIywGZto9P+aeKoiWOq/eodjFYgtozCCQFl3rLGILjOiV 3HHfhk/RO/H/KYZNcFXeCCK+EfX/j9cvHdm/z+qHK5mDR1L5VK045z+oAJrsEXFCaP KeX4rkPy3RyQL3Si1NZqQBPwfcJQWAokQKDGDXyXdbxJOr6KUgY3agb0Xxb8NCVo0B P0j1yAnu8mVQI+43vEWX38ucFx0bgxYGgKKtDx2aBrcL4oT+myqJLRltwHCl+UthTe L8U/RBFarIVow== From: Pratyush Yadav To: "David Hildenbrand (Arm)" Cc: Pratyush Yadav , 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 , "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: <297adf4c-1792-4dff-a7c8-2694dc2b1446@kernel.org> (David Hildenbrand's message of "Fri, 30 Oct 2026 13:06:45 +0100") References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> <20261029-fixes_core-v2-3-a64ce7f83abb@kernel.org> <2vxzmrrvmnil.fsf@kernel.org> <297adf4c-1792-4dff-a7c8-2694dc2b1446@kernel.org> Date: Fri, 30 Oct 2026 13:29:50 +0100 Message-ID: <2vxzik2jmkw1.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: 210FC14000B X-Stat-Signature: rh9by9co9xk8xu7ph965pt74ui4t6kd8 X-Spam-Status: No, score=-12.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,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-Rspamd-Server: rspam09 X-HE-Tag: 1793363401-137203 X-HE-Meta: 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 aFgsrGxO acR5U4+uvnWhQghBfIxxi0lzoeUG8duuXN2E4L1YO9fGmVo3KNzqZeW96//GikO13tFGn3Ct+hV8K9nzeRG+Koqti6wiKIKwfv1M6SpVOjrGbczDUEwLzYF5RakX8vHR3VVH7Enn1ABpm0AkhgX33EoL2gHkIaXjTxmu9tR9Z7zezpNQmEvGECIWJ0LzZzLLVJhD7BczapHXyKr26IwhXJCTMLM50R3Q9idF+J2vcUqPI2XOd2GrqwAokKqE6w7SfUPYlEO/6VMUkNNiB5Yl1GrJeNUFgLQwRrEm/BZXH1ZY3/UNhxVvEDi5qNhOQ85n30CpK9ofgX96pnda9+aCIOsJ9gg== 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 On Fri, Oct 30 2026, David Hildenbrand (Arm) wrote: > On 10/30/26 12:33, Pratyush Yadav wrote: >> Hi David, >> >> On Thu, Oct 29 2026, David Hildenbrand (Arm) wrote: [...] >> 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. > > Looks like collapse_file() would then use shmem_mapping() for the time > being. God this is confusing. Yes... > > What about the following replacement: > > > From 6e3c4f92a651e36ed1ae8d7659d2ca08543fa430 Mon Sep 17 00:00:00 2001 > From: "David Hildenbrand (Arm)" > Date: Sat, 24 Oct 2026 21:08:33 +0200 > Subject: [PATCH] mm/shmem: make shmem_file() check the file's inode > > shmem_file() only checks if file->f_mapping is a shmem mapping. This > mapping can belong to another file, however, as with a Coda file backed > by a tmpfs container after mmap(). > > So it does not guarantee that the file inode is an actual 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. > > Let's make shmem_file() check the inode's file operations instead, to > identify shmem inodes reliably. This will identify regular shmem inodes, > including memfds and ordinary tmpfs files, independently of wrapper file > operations. > > Use shmem_mapping() in collapse_file() instead to not change the behavior > of collapse_file(): it operates on the page cache and uses mapping->host > for shmem inode operations. Focusing on the file does not seem relevant. > > 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 > Suggested-by: Pratyush Yadav > Signed-off-by: David Hildenbrand (Arm) Looks great, thanks! Reviewed-by: Pratyush Yadav (Google) [...] -- Regards, Pratyush Yadav