From nobody Sun Dec 14 05:56:53 2025 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 58FCCCDB46E for ; Thu, 12 Oct 2023 17:04:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347353AbjJLREw (ORCPT ); Thu, 12 Oct 2023 13:04:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37434 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1379577AbjJLREl (ORCPT ); Thu, 12 Oct 2023 13:04:41 -0400 Received: from mail-wr1-x42f.google.com (mail-wr1-x42f.google.com [IPv6:2a00:1450:4864:20::42f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AF7EED6; Thu, 12 Oct 2023 10:04:39 -0700 (PDT) Received: by mail-wr1-x42f.google.com with SMTP id ffacd0b85a97d-32157c8e4c7so1158221f8f.1; Thu, 12 Oct 2023 10:04:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1697130278; x=1697735078; darn=vger.kernel.org; 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=VkUJ0oO3Mp9xCXnylh1JdkHseQH/mUhjkeml5gm5SR8=; b=EKyrHvpe3wR6P8/JJLVVlxu74L7tuvaOtZLYAV60i5Qdk9bLS5Vp4TRpQMPanXcRIG HNfal8veY8MW4jukBlswEr9s8TtYCcm/Cv7MarTEP1tLYoI3OF8xSPmTzi/kTmuM7HlJ c9ouDVCNnFEJ697ucVTGzopnAXIlHxBZk3x9Ji9MeJ34LGt/zWbRICS3wR/S/e8Bk69S a8oGXCn+LD8SME9pxhaTjkIKacFE6D6q9ANZt5xFd2syMgp+kC4UDrSD+ucLMfSrPHsg AZxgDJGmTLhqpITP2CF8ILNJhCIQ1dSHwv2ze9Yl+UoSAaB97VLpf6+lEaeQBxxiPn+w eorg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1697130278; x=1697735078; 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=VkUJ0oO3Mp9xCXnylh1JdkHseQH/mUhjkeml5gm5SR8=; b=w3zobfsJvyT4yvIfjLmWAzo2KESGNkbozblTTk5HptZ/zSRKE5NiJRe8dP31oWgY5k NTH64CeZEgbUrii/lB3TgQbfTXTVVXqYVXYC76N4QuKgT/i/afgYpI5Oh69mv/nTOYqj tur+WwIdo5TJlM7cN65zcB1PRjI80+rZJ+sOdjcdtw7cCCloPD5YjYcL5qtUX6UGEVf+ YkqM3GRwTGKCCTlgIkXAzJnPJ5F6AtM/vj9Xo61PwD8zohnRfcJQEyeNWhCvWdPXOb2l aEt4muFugEdgEFqH8t0TarHnBVPp/tmdI9O98O3DKkcRUD22xtO0KcyBt83hqC6O+E1v g8tQ== X-Gm-Message-State: AOJu0YwOBYRp4wQdbF4OqJj6WVbM+Zx9BGSuBdXEm3lkQPLJaL9JcGXV chbzpemZqCtXEyeqwKljePM= X-Google-Smtp-Source: AGHT+IGEfvOX2oiWBKkh4O/yKmWydOZ76wDsxaQCjAqvjCnNn57Y9QF5SeE6lMfg3rl+IKZUkH80og== X-Received: by 2002:a05:6000:b0f:b0:32d:9572:6469 with SMTP id dj15-20020a0560000b0f00b0032d95726469mr1470249wrb.46.1697130277811; Thu, 12 Oct 2023 10:04:37 -0700 (PDT) Received: from lucifer.home ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.googlemail.com with ESMTPSA id h16-20020adffd50000000b003197869bcd7sm18875418wrs.13.2023.10.12.10.04.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Oct 2023 10:04:36 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Matthew Wilcox , Hugh Dickins , Andy Lutomirski , Jan Kara , linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, Lorenzo Stoakes Subject: [PATCH v4 3/3] mm: perform the mapping_map_writable() check after call_mmap() Date: Thu, 12 Oct 2023 18:04:30 +0100 Message-ID: <55e413d20678a1bb4c7cce889062bbb07b0df892.1697116581.git.lstoakes@gmail.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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. There is a delicate situation with cleanup paths assuming that a writable mapping must have occurred in circumstances where it may now not have. In order to ensure we do not accidentally mark a writable file unwritable by mistake, we explicitly track whether we have a writable mapping and unmap only if we do. Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D217238 Signed-off-by: Lorenzo Stoakes --- mm/mmap.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 0041e3631f6c..7f45a08e7973 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2752,6 +2752,7 @@ unsigned long mmap_region(struct file *file, unsigned= long addr, unsigned long charged =3D 0; unsigned long end =3D addr + len; unsigned long merge_start =3D addr, merge_end =3D end; + bool writable_file_mapping =3D false; pgoff_t vm_pgoff; int error; VMA_ITERATOR(vmi, mm, addr); @@ -2846,17 +2847,19 @@ unsigned long mmap_region(struct file *file, unsign= ed long addr, vma->vm_pgoff =3D pgoff; =20 if (file) { - if (is_shared_maywrite(vm_flags)) { - error =3D mapping_map_writable(file->f_mapping); - if (error) - goto free_vma; - } - vma->vm_file =3D get_file(file); error =3D call_mmap(file, vma); if (error) goto unmap_and_free_vma; =20 + if (vma_is_shared_maywrite(vma)) { + error =3D mapping_map_writable(file->f_mapping); + if (error) + goto close_and_free_vma; + + writable_file_mapping =3D true; + } + /* * Expansion is handled above, merging is handled below. * Drivers should not alter the address of the VMA. @@ -2920,8 +2923,10 @@ unsigned long mmap_region(struct file *file, unsigne= d long addr, mm->map_count++; if (vma->vm_file) { i_mmap_lock_write(vma->vm_file->f_mapping); - if (vma_is_shared_maywrite(vma)) + if (vma_is_shared_maywrite(vma)) { mapping_allow_writable(vma->vm_file->f_mapping); + writable_file_mapping =3D true; + } =20 flush_dcache_mmap_lock(vma->vm_file->f_mapping); vma_interval_tree_insert(vma, &vma->vm_file->f_mapping->i_mmap); @@ -2937,7 +2942,7 @@ unsigned long mmap_region(struct file *file, unsigned= long addr, =20 /* Once vma denies write, undo our temporary denial count */ unmap_writable: - if (file && is_shared_maywrite(vm_flags)) + if (writable_file_mapping) mapping_unmap_writable(file->f_mapping); file =3D vma->vm_file; ksm_add_vma(vma); @@ -2985,7 +2990,7 @@ unsigned long mmap_region(struct file *file, unsigned= long addr, unmap_region(mm, &vmi.mas, vma, prev, next, vma->vm_start, vma->vm_end, vma->vm_end, true); } - if (file && is_shared_maywrite(vm_flags)) + if (writable_file_mapping) mapping_unmap_writable(file->f_mapping); free_vma: vm_area_free(vma); --=20 2.42.0