From patchwork Fri Apr 1 22:08:31 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Verkamp X-Patchwork-Id: 12798819 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 897DFC433F5 for ; Fri, 1 Apr 2022 22:08:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353219AbiDAWKn (ORCPT ); Fri, 1 Apr 2022 18:10:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47962 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353230AbiDAWKm (ORCPT ); Fri, 1 Apr 2022 18:10:42 -0400 Received: from mail-pf1-x42d.google.com (mail-pf1-x42d.google.com [IPv6:2607:f8b0:4864:20::42d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F408F33346 for ; Fri, 1 Apr 2022 15:08:50 -0700 (PDT) Received: by mail-pf1-x42d.google.com with SMTP id z16so3850789pfh.3 for ; Fri, 01 Apr 2022 15:08:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=+DU/KAvneVMZvyUwbOBCXJHatvzCCAIN7Ytl6QwY8EU=; b=cqZTfaay5ukidSBjk5VJHj3uRfyXZLHu+6BwWg5igbNAypA7YFLzCM7eBGIELFcM41 TMpSn72s+uFhNhHvOAB5qYJ+5aFs9q6EzNHjfSH4UmWO2384Lw5KgI0KRaaf7mMmoWgG 0XsVQsuI9rNDYkg9VT4YJ+gREdqlf4ss9Jdkk= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=+DU/KAvneVMZvyUwbOBCXJHatvzCCAIN7Ytl6QwY8EU=; b=yBsc2/IR03Dc7fl4Zbr9h4JLi4sTN/4QE2oBpg+GmPjZJaBrGx4FUVqufGiL9QpuB1 u98dcFsUD5IoeD6rHzhU8L0xUzXSfv/wUSwlOSTHOBqCsCOnO9bueFz73N6DKVb9BPvJ BHDkzl4Q70bpkO/8TLUppsRDw6fzrZUTiw93Ed6kk0k98v7zqB+4s2BlA++LPq3np95v QCdEwL9mFX0+QREMghh6DfU/H9VFiW8MvuETVk5mJcwRwVrxDZE02mBsJBwgzHbyCkCw /pBBwUpooQrWabMfl0yRlN50Upc/RbrPcCfNXLkmTY0a5lJxAr3grPHT15HuzZyYxLv7 FQkg== X-Gm-Message-State: AOAM531SNYS2VCHngkSCpjuX2FvjVwybJy8Wxm7Yqm19jXaxOygyN/7I YxwRzzZMqoLmEp7H0Ps7x+n9+Q== X-Google-Smtp-Source: ABdhPJy2sy1C7CXcCxIY6R92ffiHpAxC/4GSwsnETPbbVJrLVIPp8s0futQO1QalpgQMGerY3kwZOw== X-Received: by 2002:a05:6a00:1702:b0:4fd:aae0:84a1 with SMTP id h2-20020a056a00170200b004fdaae084a1mr12964808pfc.12.1648850930427; Fri, 01 Apr 2022 15:08:50 -0700 (PDT) Received: from localhost ([2620:15c:202:201:72c9:527e:d936:c24b]) by smtp.gmail.com with UTF8SMTPSA id y3-20020a056a00190300b004fa2411bb92sm4331229pfi.93.2022.04.01.15.08.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Apr 2022 15:08:50 -0700 (PDT) From: Daniel Verkamp To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Hugh Dickins , Mattias Nissler , Dmitry Torokhov , Kees Cook , Daniel Verkamp Subject: [PATCH 1/4] mm/memfd: add F_SEAL_EXEC Date: Fri, 1 Apr 2022 15:08:31 -0700 Message-Id: <20220401220834.307660-2-dverkamp@chromium.org> X-Mailer: git-send-email 2.35.1.1094.g7c7d902a7c-goog In-Reply-To: <20220401220834.307660-1-dverkamp@chromium.org> References: <20220401220834.307660-1-dverkamp@chromium.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org The new F_SEAL_EXEC flag will prevent modification of the exec bits: written as traditional octal mask, 0111, or as named flags, S_IXUSR | S_IXGRP | S_IXOTH. Any chmod(2) or similar call that attempts to modify any of these bits after the seal is applied will fail with errno EPERM. This will preserve the execute bits as they are at the time of sealing, so the memfd will become either permanently executable or permanently un-executable. Signed-off-by: Daniel Verkamp --- include/uapi/linux/fcntl.h | 1 + mm/memfd.c | 2 ++ mm/shmem.c | 6 ++++++ 3 files changed, 9 insertions(+) diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 2f86b2ad6d7e..a472ba69596c 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -43,6 +43,7 @@ #define F_SEAL_GROW 0x0004 /* prevent file from growing */ #define F_SEAL_WRITE 0x0008 /* prevent writes */ #define F_SEAL_FUTURE_WRITE 0x0010 /* prevent future writes while mapped */ +#define F_SEAL_EXEC 0x0020 /* prevent chmod modifying exec bits */ /* (1U << 31) is reserved for signed error codes */ /* diff --git a/mm/memfd.c b/mm/memfd.c index 08f5f8304746..4ebeab94aa74 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -147,6 +147,7 @@ static unsigned int *memfd_file_seals_ptr(struct file *file) } #define F_ALL_SEALS (F_SEAL_SEAL | \ + F_SEAL_EXEC | \ F_SEAL_SHRINK | \ F_SEAL_GROW | \ F_SEAL_WRITE | \ @@ -175,6 +176,7 @@ static int memfd_add_seals(struct file *file, unsigned int seals) * SEAL_SHRINK: Prevent the file from shrinking * SEAL_GROW: Prevent the file from growing * SEAL_WRITE: Prevent write access to the file + * SEAL_EXEC: Prevent modification of the exec bits in the file mode * * As we don't require any trust relationship between two parties, we * must prevent seals from being removed. Therefore, sealing a file diff --git a/mm/shmem.c b/mm/shmem.c index 529c9ad3e926..a5ca9675fc29 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1083,6 +1083,12 @@ static int shmem_setattr(struct user_namespace *mnt_userns, if (error) return error; + if ((info->seals & F_SEAL_EXEC) && (attr->ia_valid & ATTR_MODE)) { + if ((inode->i_mode ^ attr->ia_mode) & 0111) { + return -EPERM; + } + } + if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) { loff_t oldsize = inode->i_size; loff_t newsize = attr->ia_size;