From nobody Mon Apr 6 09:11:32 2026 Received: from embla.dev.snart.me (embla.dev.snart.me [54.252.183.203]) (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 1A7E88834 for ; Fri, 20 Mar 2026 04:17:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=54.252.183.203 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773980260; cv=none; b=ofIRHWZnzFaWpJpa8OJ0uZkHjie40CfhSLi5zUwTHrvvglz99BXwKCGJ7bEWd8lsoH7PtIKSq52b6EtmT/Rpdhze9DmJmRVT3OIsCIq2/olaKbxIs03EtFOe9vx8kVpOhzmXEyt5q2nRYs29l44heGtM7zkzr6Y7JU0XcMZzYj4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773980260; c=relaxed/simple; bh=3S1XvgPgrL+rXHTRZAhkX06EXZz2IEFEJVt70jHV1vs=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=bbOAdmZ6x26bqhssMzavKl94eG0QPjnZnpbv9qyCQkmoWheD4VWMlL+LY0rTCg+5bLGMxnOKAYiOYFMYKOB5TMpBxK7NYNqGgrDjb1QDb4s9Wsm0NqmZstEmohFPkyCG4Vn38+wlru9vm/F4aNeG5t77hDVULmrnHOnfLwrVzaM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=dev.snart.me; spf=pass smtp.mailfrom=dev.snart.me; dkim=pass (1024-bit key) header.d=dev.snart.me header.i=@dev.snart.me header.b=ADx/tK8Y; arc=none smtp.client-ip=54.252.183.203 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=dev.snart.me Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=dev.snart.me Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=dev.snart.me header.i=@dev.snart.me header.b="ADx/tK8Y" Received: from embla.dev.snart.me (localhost [IPv6:::1]) by embla.dev.snart.me (Postfix) with ESMTP id 8EE101D490; Fri, 20 Mar 2026 04:17:31 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 embla.dev.snart.me 8EE101D490 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=dev.snart.me; s=00; t=1773980252; bh=3S1XvgPgrL+rXHTRZAhkX06EXZz2IEFEJVt70jHV1vs=; h=From:To:Cc:Subject:Date:From; b=ADx/tK8YOhd/vux+5khYfbG2wYC7VNBoIyCABBoFHybQNu5YwmpCftjeK8QdYKwkl 4hRkcHkrz4BImqOfGaFPDQgD1at3Ig/82WDF8Yc5coqWS/zO6qxSTGF6DNLz0J1gsI zujNlE9h21ym13w4NeEvVuMyJbNtxVPqUFq0xdxw= Received: from maya.d.snart.me ([182.226.25.243]) by embla.dev.snart.me with ESMTPSA id dHc6EFvKvGm55QcA8KYfjw (envelope-from ); Fri, 20 Mar 2026 04:17:31 +0000 From: David Timber To: arnd@arndb.de, gregkh@linuxfoundation.org Cc: linux-kernel@vger.kernel.org, David Timber Subject: [PATCH] drivers/char/mem.c: fix null and zero dev lseek Date: Fri, 20 Mar 2026 13:17:22 +0900 Message-ID: <20260320041722.196759-1-dxdt@dev.snart.me> X-Mailer: git-send-email 2.53.0.1.ga224b40d3f.dirty Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" lseek() on /dev/null and /dev/zero always returns 0. This is problematic for userland programs that detect holes and advancing the offset by the delta (SEEK_HOLE - SEEK_DATA), which will always be calculated as zero. Link: https://github.com/util-linux/util-linux/pull/4132 Signed-off-by: David Timber --- drivers/char/mem.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index cca4529431f8..e2bde4ad5677 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -573,9 +573,21 @@ static ssize_t write_full(struct file *file, const cha= r __user *buf, * Special lseek() function for /dev/null and /dev/zero. Most notably, you * can fopen() both devices with "a" now. This was previously impossible. * -- SRB. + * + * For SEEK_DATA and SEEK_HOLE, return an error. Otherwise, userland confo= rming + * to the POSIX spec could end up in an infinite loop. */ static loff_t null_lseek(struct file *file, loff_t offset, int orig) { + switch (orig) { + case SEEK_CUR: + case SEEK_SET: + case SEEK_END: + break; + default: + return -EINVAL; + } + return file->f_pos =3D 0; } =20 --=20 2.53.0.1.ga224b40d3f.dirty