From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: =?UTF-8?q?Andreas=20Bie=C3=9Fmann?= To: linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Andreas=20Bie=C3=9Fmann?= , Greg Kroah-Hartman , Kay Sievers , Ben Hutchings , stable@vger.kernel.org Subject: [RESEND][PATCH v2] register_console: prevent adding the same console twice Date: Fri, 2 Aug 2013 12:23:34 +0200 Message-Id: <1375439014-13679-1-git-send-email-andreas@biessmann.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In-Reply-To: <1364201964-2990-1-git-send-email-andreas@biessmann.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: This patch guards the console_drivers list to be corrupted. The for_each_console() macro insist on a strictly forward list ended by NULL: con0->next->con1->next->NULL Without this patch it may happen easily to destroy this list for example by adding 'earlyprintk' twice, especially on embedded devices where the early console is often a single static instance. This will result in the following list: con0->next->con0 This in turn will result in an endless loop in console_unlock() later on by printing the first __log_buf line endlessly. Signed-off-by: Andreas Bießmann Cc: Greg Kroah-Hartman Cc: Kay Sievers Cc: Ben Hutchings Cc: stable@vger.kernel.org --- since v1: * use WARN() as Ben suggested * print 'already registered' instead of 'prevent registering' kernel/printk/printk.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 5b5a708..b4e8500 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2226,6 +2226,13 @@ void register_console(struct console *newcon) struct console *bcon = NULL; struct console_cmdline *c; + if (console_drivers) + for_each_console(bcon) + if (WARN(bcon == newcon, + "console '%s%d' already registered\n", + bcon->name, bcon->index)) + return; + /* * before we register a new CON_BOOT console, make sure we don't * already have a valid console -- 1.7.10.4