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 CF78D40B6FC for ; Thu, 4 Jun 2026 11:13:14 +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=1780571595; cv=none; b=SLwiPREL8+bZV6CIZAdRu4mVYP4TbYYLlxB/p3riFJ5nT1nDH+kMmRrdqUcVYMs7tLljbQr/mCFibue7pUTqRjEKHQo3vkch+/U0i5/qik2nr985dE2O79+mWcAIB6DJwyKHYWTzSyJCB1rj8fPRZ/8T/6pg2XUSBdVA5DgH9u8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780571595; c=relaxed/simple; bh=Z2xSEZ28ShpzpmW2+vB5Gfh/RanMELiUmmVTw232Y8c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hdWFi77pBDo+XtoYI80FoZnn9XVdzUa7kJRLZGe/gyaMWVtY6aVu46Mcdui/EQqZNMajnE3deXJhMe73M3A1KjX2UUMc6+AV1L4fKDued3WXZlaNEMDS/r9zuhRAaZAlqC7GVbvf2kRedUrNTSc6zqpYA1ISV/UyCpnmrZ+G4cU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fduozU+y; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fduozU+y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A9E21F00893; Thu, 4 Jun 2026 11:13:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780571594; bh=Us1Fbpbdus84BcYaPgI7jLYVned3A5mxQc2I32XFOZs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=fduozU+yw4SQb1ObXJUNRc4jOxNydpmr/hWsvxI8VCGqoBOU0HF2zsdFeBw7wm2Vw nEfqSM8KUdeKfl6fZw7dHlQbp/eWQy8ZbAdj3BIGXJpsgdJYPG15XfXAWvNMow0HMB xBFYE693UlGUqRZ0LYjKcyFkN+KR9Grgz2/JCaxKLJQKOt+vapyLZUQrbYS8shNTYe BHmq8SxV54WKDtBh/ezYm6m30lJdUwJZ0nFpkBq7FpI4KZdtYNmUakKCOujErI1rmj M1tRpTut+H5elq3nryuLvIeGKznbCJYwFjBia5Wnaa54K26QWh4JBKZhLLXkMJY5oj P9/ezxun9UJMg== From: Sasha Levin To: stable@vger.kernel.org Cc: "Pratyush Yadav (Google)" , Pasha Tatashin , Jeff Xu , Baolin Wang , Brendan Jackman , Greg Thelen , Hugh Dickins , Kees Cook , "David Hildenbrand (Arm)" , Andrew Morton , Sasha Levin Subject: [PATCH 6.18.y] memfd: deny writeable mappings when implying SEAL_WRITE Date: Thu, 4 Jun 2026 07:13:11 -0400 Message-ID: <20260604111311.3206451-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026060407-bust-ashes-06a9@gregkh> References: <2026060407-bust-ashes-06a9@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Pratyush Yadav (Google)" [ Upstream commit 3b041514cb6eae45869b020f743c14d983363222 ] 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: Sasha Levin --- mm/memfd.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/mm/memfd.c b/mm/memfd.c index a405eaa451ee8b..f7ba1e9dea49a0 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -284,6 +284,12 @@ static int memfd_add_seals(struct file *file, unsigned int seals) 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 *file, unsigned int seals) } } - /* - * 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; -- 2.53.0