From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793370953; b=SLrWcpMGzCxKu0CYeuAuFZe345LVgVhQOacd01nOIUhNQOkuqr9rSVlnjAZJLQMWe4cH gOvJkdlUcJrjicD3CioEyDK3SKoCF2ve45BS4sWm3Ug2Uj1EEXKOj9ZSZ7r7Z8sq/Ggu6 7dYwa5aWzhO6vLyLSD0BtCAL6uhtUz7i3ESrxtVFPn+MKJX2a0F8u7I8vjh9sMUkV1vE/ 5yv6ESdNiU2Iz6sSWz7GXUC1cbfbtyxkJJ+643ya/XtTbNtYDF7h/gNT9XRI/oMptwC+b t/k0uhLDtKO1uazudzeZbW5X0YPbw5MjZmXk0FBcziRnvGXRzEXgC8E2EivdvLQymbw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793370953; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=y6XXbQ+HdgQmOTZa0aEBan+zjL/ycrb6TKGl8S7Q83w=; b=vPKo/UdW/Ng7SC5a0MtE2ZjKfY2mFdJk8tFWio5kwasVHbpyiDUsC02R4Ht9yGXEEkJ1 OtE/84F9xZWyLkeNezLDAT3ptdFxnbb8svs1dFTaIe2E9zNOXW6sYWQ8rIngtpDcqDGE+ CHMM6s8Q9qByW39LzOBM9rTHwLLYGVFvdO7PUTBzSYkxBdrLn3HturFkj7vJVynvOCpJY j9QNiGgK4uejI5Y21bxRNnf4RT5or43k9Zn3JAycEOKjtAdHL4/iZI2K/PxSzo06UIAY9 bY0FI6PzNENyOCMcwRoiW9/2x4VHlhWAt83SS0BMAj9dbtibvC5cmIxDPePGKX7mQjg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Zc8ZNVO6; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B0B0E606A31A; Fri, 30 Oct 2026 14:35:52 +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=Zc8ZNVO6 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 697CF1F0093A; Fri, 30 Oct 2026 14:35:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793370952; bh=y6XXbQ+HdgQmOTZa0aEBan+zjL/ycrb6TKGl8S7Q83w=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Zc8ZNVO6uRM/ebf2tyuqkNg2F+fe5LIUT6QCAumzzPpOuGmyXnfnNO5s9RSYLm2rE jwJf7qLnqMB1Nf2QO0gP2HzziZZK6letMz6x4Z1QebhXjhx6Lp5o3hUiQQDX2zhFLu 5wWBHnZAqJxpm4krMusfEm0ziwpBACmY2PLnP7EQIV+ROXKrDC2x0Z413kzf7TnVRa 1IzLYX7Ri/ykqtCagS6CsHGxfJq/AfR5jwjpZPHtLQClzkqVrG8JQ9OGKa/yrF53ml FKD/f6zB3W/UEBSdx5AyFtTg6EeOre5o75pbwDLQQv3rT/OAi7RJN7FszZ+57tVf4M radtUUXIQvVSg== Message-ID: <43994c77-bde2-47cc-b6bd-5b479672bad2@kernel.org> Date: Fri, 30 Oct 2026 15:35:33 +0100 X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 03/47] mm/memfd: check for real shmem inodes before accessing shmem state To: Pratyush Yadav 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 , "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 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> <2vxzik2jmkw1.fsf@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <2vxzik2jmkw1.fsf@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/30/26 13:29, Pratyush Yadav wrote: > On Fri, Oct 30 2026, David Hildenbrand (Arm) wrote: > >> On 10/30/26 12:33, Pratyush Yadav wrote: >>> Hi David, >>> > [...] >>> 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) Thanks! @Mike, @Rik, Ill drop your RB, so please re-review. -- Cheers, David