From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946244Ab2LFRJo (ORCPT ); Thu, 6 Dec 2012 12:09:44 -0500 Received: from gibson.whatever-company.com ([87.98.251.113]:39598 "EHLO gibson.whatever-company.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946199Ab2LFRJk (ORCPT ); Thu, 6 Dec 2012 12:09:40 -0500 From: Sylvain Munaut To: torvalds@linux-foundation.org Cc: linux-kernel@vger.kernel.org, Sylvain Munaut , Kay Sievers , stable@kernel.org Subject: [PATCH] printk: Fix print_time length computation when no buffer is given Date: Thu, 6 Dec 2012 18:09:35 +0100 Message-Id: <1354813775-32451-1-git-send-email-s.munaut@whatever-company.com> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The "%5lu" part of the sprintf only guarantees a minimum length, not a maximum one. This patch should make it correct for any possible timestamp. This problem dates back from the printk conversion to records AFAICT. I've tested this locally both by verifying 'dmesg' no longer segfaulted and also by checking that before this patch the buffer was overrun by exactly the number of char corresponding to extra digits in the timestamps. Cc: Kay Sievers Cc: stable@kernel.org Signed-off-by: Sylvain Munaut --- kernel/printk.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/printk.c b/kernel/printk.c index 66a2ea3..2ceceea 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -847,8 +847,17 @@ static size_t print_time(u64 ts, char *buf) if (!printk_time) return 0; - if (!buf) - return 15; + if (!buf) { + size_t len = 15; + u64 ts_limit = (u64)100000 * (u64)1000000000; + + while ((ts > ts_limit) && (len < 21)) { + len++; + ts_limit = 10 * ts_limit; + } + + return len; + } rem_nsec = do_div(ts, 1000000000); return sprintf(buf, "[%5lu.%06lu] ", -- 1.7.10.4