From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 52732C43381 for ; Sun, 24 Mar 2019 10:28:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 290B7222C1 for ; Sun, 24 Mar 2019 10:28:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728700AbfCXK2P (ORCPT ); Sun, 24 Mar 2019 06:28:15 -0400 Received: from avasout02.plus.net ([212.159.14.17]:47283 "EHLO avasout02.plus.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728642AbfCXK2P (ORCPT ); Sun, 24 Mar 2019 06:28:15 -0400 Received: from deneb ([80.229.24.9]) by smtp with ESMTP id 80MMh60E72SW580MNhM3SG; Sun, 24 Mar 2019 10:28:13 +0000 X-CM-Score: 0.00 X-CNFS-Analysis: v=2.3 cv=NtavjPVJ c=1 sm=1 tr=0 a=E/9URZZQ5L3bK/voZ0g0HQ==:117 a=E/9URZZQ5L3bK/voZ0g0HQ==:17 a=NTGMnVQrEZIA:10 a=CCpqsmhAAAAA:8 a=-An2I_7KAAAA:8 a=9qxNCY_qAAAA:8 a=VwQbUJbxAAAA:8 a=D19gQVrFAAAA:8 a=w-YdG8ML7ShXMl4_PY4A:9 a=ul9cdbp4aOFLsgKbc677:22 a=Sq34B_EcNBM9_nrAYB9S:22 a=A2X48xt2e1hG9NJDz63Y:22 a=AjGcO6oz07-iQ99wixmX:22 a=W4TVW4IDbPiebHqcZpNg:22 Received: from mac by deneb with local (Exim 4.89) (envelope-from ) id 1h80ML-0001xW-Mk; Sun, 24 Mar 2019 10:28:09 +0000 From: Mike Crowe To: linux-kernel@vger.kernel.org Cc: Mike Crowe , Kay Sievers , Arnd Bergmann , Alexander Sverdlin , stable@vger.kernel.org Subject: [PATCH] kmsg: Return -ESPIPE rather than EBADF from llseek(SEEK_CUR) Date: Sun, 24 Mar 2019 10:27:13 +0000 Message-Id: <20190324102712.1488-1-mac@mcrowe.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CMAE-Envelope: MS4wfJl/CbTQc6m3M9qqf2LC9OSlcDhslkxIQU+lrsy3VpN2QmPF5yAQrfmdAL1uVVSiMq/3FkTlEOZTMBN5P6643y9Fjz4RwGO38TyBWYFNhYl1e1YlBIoG 5NFrtdcr2xXiwgj9c5SmXRFwGr7zBNowkE8WwawjIPFMX9B95pFplnAw Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org glibc's dprintf implementation tries to determine the current file position by calling lseek(fd, 0, SEEK_CUR). Unfortunately it treats receiving EINVAL as an error. See https://sourceware.org/bugzilla/show_bug.cgi?id=17830 >From what I can tell prior to Kay Sievers printk record commit e11fea92e13fb91c50bacca799a6131c81929986, calling lseek(fd, 0, SEEK_CUR) with such a file descriptor would not return an error. Prior to Kay's change, Arnd Bergmann's commit 6038f373a3dc1f1c26496e60b6c40b164716f07e seemed to go to some lengths to preserve the successful return code rather than returning (the perhaps more logical) -ESPIPE. glibc is happy with either a successful return or -ESPIPE. It seems that the consensus is to return -ESPIPE in this situation. Alexander Sverdlin supplied this test case: --8<-- #define _GNU_SOURCE #include #include int main(int argc, char **argv) { return dprintf(open("/dev/kmsg", O_WRONLY), "\n") < 0; } -->8-- Signed-off-by: Mike Crowe Cc: Arnd Bergmann Tested-by: Alexander Sverdlin Cc: stable@vger.kernel.org Fixes: e11fea92e1 ("kmsg: export printk records to the /dev/kmsg interface") --- kernel/printk/printk.c | 5 +++++ 1 file changed, 5 insertions(+) Originally posted as https://lkml.org/lkml/2015/1/15/575 . Thanks to Alexander for waking this up and helping to test the updated fix. diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 02ca827b8fac..4f047b13162c 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -945,6 +945,11 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) user->idx = log_next_idx; user->seq = log_next_seq; break; + case SEEK_CUR: + /* For compatibility with userspace expecting SEEK_CUR + * to not yield EINVAL. */ + ret = -ESPIPE; + break; default: ret = -EINVAL; } -- 2.20.1