From patchwork Mon Apr 3 22:28:30 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lorenzo Stoakes X-Patchwork-Id: 13198883 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E834AC77B6E for ; Mon, 3 Apr 2023 22:28:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233755AbjDCW2r (ORCPT ); Mon, 3 Apr 2023 18:28:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233671AbjDCW2p (ORCPT ); Mon, 3 Apr 2023 18:28:45 -0400 Received: from mail-wm1-x334.google.com (mail-wm1-x334.google.com [IPv6:2a00:1450:4864:20::334]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 486D430F5; Mon, 3 Apr 2023 15:28:44 -0700 (PDT) Received: by mail-wm1-x334.google.com with SMTP id j18-20020a05600c1c1200b003ee5157346cso20729995wms.1; Mon, 03 Apr 2023 15:28:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680560923; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=2ox0Um/keFFcr+KeFLWWO5PQW7Wkw7x46JWiMcUucBs=; b=IqTEJ0a+DVsrR/sbp6wFzGCaIOKJMW2b/WluK/3q1KwlzFGr2XzC9qJuUJ7AIX2xu4 VYIERbGy4I05j29jD4GWHjBV6ImJSUz3sPPYuaiG3eLJPvg+F+AqPRyHgH2bhv2l56db zk8hKNxoUPqZbK88nvjMALCegh67BbKKtQfC7K4kazXrlMz9cSLjgulHxeThVTE8rvUZ +x99D6LZswyN/OkVpXX8XP5JnB1VyMyEIIhBPweYAiR35zd9A+eqrd5RweuIO7ZYe3W4 yj9WMI0QJSNhWPnu7pDAnkoH6MTQRMYht7Ep7qdnI4WgFp8Z9VNNwFDLyS4XbvTKlWXa cJnA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680560923; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=2ox0Um/keFFcr+KeFLWWO5PQW7Wkw7x46JWiMcUucBs=; b=580VwcHehrfR3oIBYhjoXJI/NrlRJP+XnbXBl5mPbuxMcuGu3QcGSHeST6Vj7qi9+w OK2Ffz47Djw59DVi9OpFzUCjI590vY3QNdkeJYOve0Yp4/LNGlQ5iHcW9x29w4UfkIAM AcbYA+/Ts5D86zLt4sJ3MWcES5aLicLsod14MDPxH4AvVzE7bZUEi6T6VQF88wbLG3Aq VAinO3EoQpp6iCWSMyLRQuJTSNDnqLF+/da1nIHfhOgIy1tE+x1Yb5ZYfvw+SyCRXjag lVSoDyEBdHDv8MONI6RaEC9UDr0qEbqbJLXPrMy649Kk1F4/l+LfFflmyVxGdS4hFBlW Js0g== X-Gm-Message-State: AAQBX9fx8KRnLGtiq0fBPYSJdmQLcL+pTQAwDidPW8f9PxaMIyRXYeIZ /1FtFgQtLQAgWexejCRIUSE= X-Google-Smtp-Source: AKy350aFpMa5YFdkK6pkYk/H9LFfFmuJSQcyDrwohfghPSBYhva0NoXvbaDDHu8LijJ6wMsZJSfFTA== X-Received: by 2002:a05:600c:2286:b0:3ed:e6c8:f11d with SMTP id 6-20020a05600c228600b003ede6c8f11dmr641590wmf.7.1680560922635; Mon, 03 Apr 2023 15:28:42 -0700 (PDT) Received: from lucifer.home (host86-156-84-164.range86-156.btcentralplus.com. [86.156.84.164]) by smtp.googlemail.com with ESMTPSA id u17-20020a05600c19d100b003dd1bd0b915sm20731309wmq.22.2023.04.03.15.28.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Apr 2023 15:28:41 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Matthew Wilcox , Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Andy Lutomirski , Lorenzo Stoakes Subject: [RFC PATCH 1/3] mm: drop the assumption that VM_SHARED always implies writable Date: Mon, 3 Apr 2023 23:28:30 +0100 Message-Id: <691c33e2fe8fc0fd879374739b50af48524175a3.1680560277.git.lstoakes@gmail.com> X-Mailer: git-send-email 2.40.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org There are places in the kernel where there is an implicit assumption that VM_SHARED VMAs must either be writable or might become writable via e.g. mprotect(). We can explicitly check for the writable, shared case while remaining conservative - If VM_MAYWRITE is not set then, by definition, the memory can never be written to. Update these checks to also check for VM_MAYWRITE. Suggested-by: Andy Lutomirski Signed-off-by: Lorenzo Stoakes --- include/linux/fs.h | 4 ++-- include/linux/mm.h | 11 +++++++++++ kernel/fork.c | 2 +- mm/filemap.c | 2 +- mm/madvise.c | 2 +- mm/mmap.c | 12 ++++++------ 6 files changed, 22 insertions(+), 11 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index c85916e9f7db..373e1edd719c 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -410,7 +410,7 @@ extern const struct address_space_operations empty_aops; * It is also used to block modification of page cache contents through * memory mappings. * @gfp_mask: Memory allocation flags to use for allocating pages. - * @i_mmap_writable: Number of VM_SHARED mappings. + * @i_mmap_writable: Number of VM_SHARED, VM_MAYWRITE mappings. * @nr_thps: Number of THPs in the pagecache (non-shmem only). * @i_mmap: Tree of private and shared mappings. * @i_mmap_rwsem: Protects @i_mmap and @i_mmap_writable. @@ -513,7 +513,7 @@ static inline int mapping_mapped(struct address_space *mapping) /* * Might pages of this file have been modified in userspace? - * Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap + * Note that i_mmap_writable counts all VM_SHARED, VM_MAYWRITE vmas: do_mmap * marks vma as VM_SHARED if it is shared, and the file was opened for * writing i.e. vma may be mprotected writable even if now readonly. * diff --git a/include/linux/mm.h b/include/linux/mm.h index 898ece0a3802..8e64041b1703 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -862,6 +862,17 @@ static inline bool vma_is_accessible(struct vm_area_struct *vma) return vma->vm_flags & VM_ACCESS_FLAGS; } +static inline bool is_shared_maywrite(vm_flags_t vm_flags) +{ + return (vm_flags & (VM_SHARED | VM_MAYWRITE)) == + (VM_SHARED | VM_MAYWRITE); +} + +static inline bool vma_is_shared_maywrite(struct vm_area_struct *vma) +{ + return is_shared_maywrite(vma->vm_flags); +} + static inline struct vm_area_struct *vma_find(struct vma_iterator *vmi, unsigned long max) { diff --git a/kernel/fork.c b/kernel/fork.c index 2066a57786a8..58f257d60fee 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -733,7 +733,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, get_file(file); i_mmap_lock_write(mapping); - if (tmp->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(tmp)) mapping_allow_writable(mapping); flush_dcache_mmap_lock(mapping); /* insert tmp into the share list, just after mpnt */ diff --git a/mm/filemap.c b/mm/filemap.c index a34abfe8c654..4d896515032c 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3607,7 +3607,7 @@ int generic_file_mmap(struct file *file, struct vm_area_struct *vma) */ int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma) { - if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) + if (vma_is_shared_maywrite(vma)) return -EINVAL; return generic_file_mmap(file, vma); } diff --git a/mm/madvise.c b/mm/madvise.c index 340125d08c03..606c395c4ddd 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -981,7 +981,7 @@ static long madvise_remove(struct vm_area_struct *vma, return -EINVAL; } - if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE)) + if (!vma_is_shared_maywrite(vma)) return -EACCES; offset = (loff_t)(start - vma->vm_start) diff --git a/mm/mmap.c b/mm/mmap.c index 51cd747884e3..c96dcce90772 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -106,7 +106,7 @@ void vma_set_page_prot(struct vm_area_struct *vma) static void __remove_shared_vm_struct(struct vm_area_struct *vma, struct file *file, struct address_space *mapping) { - if (vma->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(vma)) mapping_unmap_writable(mapping); flush_dcache_mmap_lock(mapping); @@ -427,7 +427,7 @@ static unsigned long count_vma_pages_range(struct mm_struct *mm, static void __vma_link_file(struct vm_area_struct *vma, struct address_space *mapping) { - if (vma->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(vma)) mapping_allow_writable(mapping); flush_dcache_mmap_lock(mapping); @@ -2596,7 +2596,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma->vm_pgoff = pgoff; if (file) { - if (vm_flags & VM_SHARED) { + if (is_shared_maywrite(vm_flags)) { error = mapping_map_writable(file->f_mapping); if (error) goto free_vma; @@ -2671,7 +2671,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma_iter_store(&vmi, vma); mm->map_count++; if (vma->vm_file) { - if (vma->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(vma)) mapping_allow_writable(vma->vm_file->f_mapping); flush_dcache_mmap_lock(vma->vm_file->f_mapping); @@ -2688,7 +2688,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, /* Once vma denies write, undo our temporary denial count */ unmap_writable: - if (file && vm_flags & VM_SHARED) + if (file && is_shared_maywrite(vm_flags)) mapping_unmap_writable(file->f_mapping); file = vma->vm_file; expanded: @@ -2734,7 +2734,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, unmap_region(mm, &mm->mm_mt, vma, prev, next, vma->vm_start, vma->vm_end, true); } - if (file && (vm_flags & VM_SHARED)) + if (file && is_shared_maywrite(vm_flags)) mapping_unmap_writable(file->f_mapping); free_vma: vm_area_free(vma); From patchwork Mon Apr 3 22:28:31 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lorenzo Stoakes X-Patchwork-Id: 13198889 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F5CEC76196 for ; Mon, 3 Apr 2023 22:28:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233796AbjDCW24 (ORCPT ); Mon, 3 Apr 2023 18:28:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233719AbjDCW2r (ORCPT ); Mon, 3 Apr 2023 18:28:47 -0400 Received: from mail-wm1-x32a.google.com (mail-wm1-x32a.google.com [IPv6:2a00:1450:4864:20::32a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B958730C1; 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[86.156.84.164]) by smtp.googlemail.com with ESMTPSA id u17-20020a05600c19d100b003dd1bd0b915sm20731309wmq.22.2023.04.03.15.28.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Apr 2023 15:28:43 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Matthew Wilcox , Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Andy Lutomirski , Lorenzo Stoakes Subject: [RFC PATCH 2/3] mm: update seal_check_[future_]write() to include F_SEAL_WRITE as well Date: Mon, 3 Apr 2023 23:28:31 +0100 Message-Id: <75478249600532faab441e43f73d4d04582efcc3.1680560277.git.lstoakes@gmail.com> X-Mailer: git-send-email 2.40.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Check for F_SEAL_WRITE as well for which the precise same logic can reasonably be applied, however so far this code will simply not be run as the mapping_map_writable() call occurs before shmem_mmap() or hugetlbfs_file_mmap() and thus would error out in the case of a read-only shared mapping before the logic could be applied. This therefore has no impact until the following patch which changes the order in which the *_mmap() functions are called. Signed-off-by: Lorenzo Stoakes --- fs/hugetlbfs/inode.c | 2 +- include/linux/mm.h | 13 +++++++------ mm/shmem.c | 2 +- 3 files changed, 9 insertions(+), 8 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 702d79639c0d..8ab8840707ac 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -135,7 +135,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma) vm_flags_set(vma, VM_HUGETLB | VM_DONTEXPAND); vma->vm_ops = &hugetlb_vm_ops; - ret = seal_check_future_write(info->seals, vma); + ret = seal_check_write(info->seals, vma); if (ret) return ret; diff --git a/include/linux/mm.h b/include/linux/mm.h index 8e64041b1703..ddf1b35b9dbb 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3775,16 +3775,17 @@ static inline void mem_dump_obj(void *object) {} #endif /** - * seal_check_future_write - Check for F_SEAL_FUTURE_WRITE flag and handle it + * seal_check_write - Check for F_SEAL_WRITE or F_SEAL_FUTURE_WRITE flag and + * handle it. * @seals: the seals to check * @vma: the vma to operate on * - * Check whether F_SEAL_FUTURE_WRITE is set; if so, do proper check/handling on - * the vma flags. Return 0 if check pass, or <0 for errors. + * Check whether F_SEAL_WRITE or F_SEAL_FUTURE_WRITE are set; if so, do proper + * check/handling on the vma flags. Return 0 if check pass, or <0 for errors. */ -static inline int seal_check_future_write(int seals, struct vm_area_struct *vma) +static inline int seal_check_write(int seals, struct vm_area_struct *vma) { - if (seals & F_SEAL_FUTURE_WRITE) { + if (seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) { /* * New PROT_WRITE and MAP_SHARED mmaps are not allowed when * "future write" seal active. @@ -3793,7 +3794,7 @@ static inline int seal_check_future_write(int seals, struct vm_area_struct *vma) return -EPERM; /* - * Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as + * Since an F_SEAL_[FUTURE_]WRITE sealed memfd can be mapped as * MAP_SHARED and read-only, take care to not allow mprotect to * revert protections on such mappings. Do this only for shared * mappings. For private mappings, don't need to mask diff --git a/mm/shmem.c b/mm/shmem.c index 9218c955f482..863f2ff9fab8 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2313,7 +2313,7 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma) struct shmem_inode_info *info = SHMEM_I(inode); int ret; - ret = seal_check_future_write(info->seals, vma); + ret = seal_check_write(info->seals, vma); if (ret) return ret; From patchwork Mon Apr 3 22:28:32 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lorenzo Stoakes X-Patchwork-Id: 13198890 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5A7D4C761AF for ; Mon, 3 Apr 2023 22:28:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233811AbjDCW25 (ORCPT ); Mon, 3 Apr 2023 18:28:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45804 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233731AbjDCW2r (ORCPT ); Mon, 3 Apr 2023 18:28:47 -0400 Received: from mail-wm1-x334.google.com (mail-wm1-x334.google.com [IPv6:2a00:1450:4864:20::334]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0E7B130F5; Mon, 3 Apr 2023 15:28:46 -0700 (PDT) Received: by mail-wm1-x334.google.com with SMTP id j18-20020a05600c1c1200b003ee5157346cso20730041wms.1; Mon, 03 Apr 2023 15:28:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680560925; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=D59V0g1YvYLKaUmx+LEoYjgFSrxRUczBZA1IoL7nlYU=; b=ETUrq2dY/Th4/JHEziKKqYHg+tGm411FZ0fvvHq7s2C38in0y6R3FaxLNn9Kj4sfr5 hMJgMJxsbvF+BQgibzC+VXG3bGSBAb1bW4IvDlePIroB7DzmvbD6AWL2l9Z+RxPcY2WH e3sRnk04MJf9JH+FTi70FLSupZ6xGpBWo6zhyM9EZJ3bUjmIhDmWb96l+t7TFGW18cS4 XhCagKRR19FhXNYIQfhhdh3fFJuSMOK5zHlYLX6Y/ZnRF/FdaP4FCYLzfxbyA7ummcqS lt4TjRqAoKPJLEu67p5KRYcTNockAGGP5JK2eJ2/xlawuQsKJgzPEOO4uoLNh7wk8jwv q2GQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680560925; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=D59V0g1YvYLKaUmx+LEoYjgFSrxRUczBZA1IoL7nlYU=; b=UIOGUYrI5cptsyBsVxcEDel0+U9d7fDepWhniWn/D2I04MIXfGYsH1vsKugXnJY33x aiWfasUTSRsAIKtHsJiqj97xsYD+PuU534JUpqoAZQevDHq35qFH9e4rMUqRh7COEGyD sPYzjbU5fwST190Z4pBnfKZa7aWGkV2yab7RECsoFQ7HGEY3EwZtkbzOq9zWdp6yJE4C 5wIXV0tlP6owbBtWVI/AztI0aS7vO4wpMeodfwp96ycsX3lykM/oB3VLxtKCtKmC47bf qJNqspofckPKIEhjxJhftsKlXPUFS4bIUwAl4l9TVh5hp0ffM3RviAWldIFQkmqRLHah y6rw== X-Gm-Message-State: AAQBX9dTRWt/OJ7StJXg7zTIQ1H4xi4T9EpofWusQ9fT9e4U+ff3KNnL ctEeJe1er3IRrh3mshaqTGoDMDtpwLI= X-Google-Smtp-Source: AKy350ZVfZY+bYiGepG6A9AZTHxDk2DIr9A7q/H3Bvhr9tEy2Ebxbza9JcTDslpZpvZNO6szjA4rCA== X-Received: by 2002:a1c:6a19:0:b0:3ed:2ae9:6c75 with SMTP id f25-20020a1c6a19000000b003ed2ae96c75mr593443wmc.37.1680560925406; Mon, 03 Apr 2023 15:28:45 -0700 (PDT) Received: from lucifer.home (host86-156-84-164.range86-156.btcentralplus.com. [86.156.84.164]) by smtp.googlemail.com with ESMTPSA id u17-20020a05600c19d100b003dd1bd0b915sm20731309wmq.22.2023.04.03.15.28.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Apr 2023 15:28:44 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Matthew Wilcox , Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Andy Lutomirski , Lorenzo Stoakes Subject: [RFC PATCH 3/3] mm: perform the mapping_map_writable() check after call_mmap() Date: Mon, 3 Apr 2023 23:28:32 +0100 Message-Id: X-Mailer: git-send-email 2.40.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to clear VM_MAYWRITE, we must be able to invoke the appropriate vm_ops->mmap() handler to do so. We would otherwise fail the mapping_map_writable() check before we had the opportunity to avoid it. This patch moves this check after the call_mmap() invocation. Only memfd actively denies write access causing a potential failure here (in memfd_add_seals()), so there should be no impact on non-memfd cases. This patch makes the userland-visible change that MAP_SHARED, PROT_READ mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed. Signed-off-by: Lorenzo Stoakes --- mm/mmap.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index c96dcce90772..a166e9f3c474 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2596,17 +2596,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma->vm_pgoff = pgoff; if (file) { - if (is_shared_maywrite(vm_flags)) { - error = mapping_map_writable(file->f_mapping); - if (error) - goto free_vma; - } - vma->vm_file = get_file(file); error = call_mmap(file, vma); if (error) goto unmap_and_free_vma; + if (vma_is_shared_maywrite(vma)) { + error = mapping_map_writable(file->f_mapping); + if (error) + goto unmap_and_free_vma; + } + /* * Expansion is handled above, merging is handled below. * Drivers should not alter the address of the VMA.