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 052437404E for ; Fri, 5 Jun 2026 00:34:54 +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=1780619696; cv=none; b=quACnsnY83loqL2c9Kfy+2x0oaPZDkit8ItmjVpFvCqqAHzS60pF8mDe2lAWjHQuOKZLLB1D4KsgS7dNxXTnnmmQkRo5yBd2UmKahB4m60FS9QQV/Nauj46LH6u7OlSbFmqC6G9aBrnNCeb7KKbEthtI64FYMSTPa6m/7sCz4Eo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780619696; c=relaxed/simple; bh=Zd6wnzqiYFXETEvAeD1R7xqqyUMchyPAjtyEYNsDLDM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=uh4+mm6+2Xcm6osIohpboXOF0mrMmC4G2TP1ZPMxtcCbDJiny9ns6wCVmIPedZj6HJYM3T1CjtDXbeOzbZR8aialMC7N3rVVbwB5w7WFVBPSi14Uo7I0YkaWSmO8k1fUIjwlid4BvU+iRlygUOanBVdHlTexGhEuOPOgRGhTfyY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=n7pG0XHI; 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="n7pG0XHI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 843EB1F00893; Fri, 5 Jun 2026 00:34:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780619694; bh=yPSQCejx+rY121F0e6r8BjOMx3ymM5OE7PjgqPUE8Hw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=n7pG0XHINPmzCpT51QNyIGy+1wp7SIk2GjGjgAuBQ1G+5L62Xm2GABWXsnOHMNv66 tHQ2iA16mN+jCu1YYtDvPn/d1JmtSRZqhFFruRVDY59Yoh3sdLlvl/XPxY5n7gvGmz GMAqN3sZa/D4jub2QSQllhVsN187UtYVngORcyS8hppylWyVrnXi7h4z56cMEBXy6N 0dg0zwyzwFnArFwsTCjd/7JuGZEMyiWP/4de3dHd9jbH4kYKLeVPdeVouTBRN8oaC+ QwSaZ3yMdQ4kxZHa9fh5KDrSjdZo9KUkxoNAK9IZdo6i1nMayG7YUCRhMaIKVnm/De KwZG9WJj//vEw== 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 6.6.y] memfd: deny writeable mappings when implying SEAL_WRITE Date: Thu, 4 Jun 2026 20:34:51 -0400 Message-ID: <20260605003451.2707256-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026060409-tightness-iodize-c0fc@gregkh> References: <2026060409-tightness-iodize-c0fc@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 187265dc68f5e8..16dde40afd324b 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -210,6 +210,12 @@ 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) @@ -222,12 +228,6 @@ static int memfd_add_seals(struct file *file, unsigned int seals) } } - /* - * SEAL_EXEC implys 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