From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 16EB91C5F27; Sun, 7 Jun 2026 10:27:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780828056; cv=none; b=CiMpw1sygByZ557h6gGN4PUM8/mdQF83cjKgt5Bx013054ebwgMQYE8o2lywhJJo/kUM0Mz8qB+4D0V6a3C71FaV6znCaPCuWu0yfXGgiYffGy0r/nNtYBK/e9114OFUy8fwB60CpvtA/ihBYeI5IVDmQF1JRSqfOenWj88hKko= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780828056; c=relaxed/simple; bh=KZNbvooBaBlsTS7bCPsXKutY8m5Mhov9lCEA2SLvvZQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HCPKofxttZA0pU1RiTPqn4HCwfWNYajvWixm1ByHgxXWNbn1kVT010ASxEMNy1FM4M9D2QSMHXeum7F+uhfNQT3tYmWM9QuB9frJ/kKUxHMS+B500F5Y7gRIIHWTfnm26kKUU3Nw1+n3K8o60higKrWp+crCSmqgjPL5gHGYmgE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=oPqf7S4x; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="oPqf7S4x" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1D9721F00893; Sun, 7 Jun 2026 10:27:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780828055; bh=2V0dwLcxcrx19ts06zdnzQ364/Do0lrJw/CixTEMXrw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=oPqf7S4xC6wEySHs7OogwoGtgyXd7//UD+bXEGVBF6fUMwKM9R/drn9qx02cD4qhH M1PTDlZZUKILtAIF7LWxAbUDPbCv4yOvONI+8BdPbXYfFSVvaGPNXVOxUhFIQVeL6V FwnKTEjLlC9enMVux22Pz5fbsY8g8NvC9cQ9ofsc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Pratyush Yadav (Google)" , Pasha Tatashin , Jeff Xu , Baolin Wang , Brendan Jackman , Greg Thelen , Hugh Dickins , Kees Cook , "David Hildenbrand (Arm)" , Andrew Morton Subject: [PATCH 6.18 124/315] memfd: deny writeable mappings when implying SEAL_WRITE Date: Sun, 7 Jun 2026 11:58:31 +0200 Message-ID: <20260607095732.176645045@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260607095727.528828913@linuxfoundation.org> References: <20260607095727.528828913@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Pratyush Yadav (Google) commit 3b041514cb6eae45869b020f743c14d983363222 upstream. When SEAL_EXEC is added, SEAL_WRITE is implied to make W^X. But the implied seal is set after the check that makes sure the memfd can not have any writable mappings. This means one can use SEAL_EXEC to apply SEAL_WRITE while having writeable mappings. This breaks the contract that SEAL_WRITE provides and can be used by an attacker to pass a memfd that appears to be write sealed but can still be modified arbitrarily. Fix this by adding the implied seals before the call for mapping_deny_writable() is done. Link: https://lore.kernel.org/20260505133922.797635-1-pratyush@kernel.org Fixes: c4f75bc8bd6b ("mm/memfd: add write seals when apply SEAL_EXEC to executable memfd") Signed-off-by: Pratyush Yadav (Google) Reviewed-by: Pasha Tatashin Acked-by: Jeff Xu Cc: Baolin Wang Cc: Brendan Jackman Cc: Greg Thelen Cc: Hugh Dickins Cc: Kees Cook Cc: "David Hildenbrand (Arm)" Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/memfd.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) --- a/mm/memfd.c +++ b/mm/memfd.c @@ -284,6 +284,12 @@ static int memfd_add_seals(struct file * goto unlock; } + /* + * SEAL_EXEC implies SEAL_WRITE, making W^X from the start. + */ + if (seals & F_SEAL_EXEC && inode->i_mode & 0111) + seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE; + if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) { error = mapping_deny_writable(file->f_mapping); if (error) @@ -296,12 +302,6 @@ static int memfd_add_seals(struct file * } } - /* - * SEAL_EXEC implies SEAL_WRITE, making W^X from the start. - */ - if (seals & F_SEAL_EXEC && inode->i_mode & 0111) - seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE; - *file_seals |= seals; error = 0;