linux-kernel - Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 11 Jan 2018 13:58:17 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Tejun Heo <tj@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        rostedt@...e.goodmis.org, Byungchul Park <byungchul.park@....com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

On (01/10/18 13:05), Steven Rostedt wrote:
[..]
> My solution takes printk from its current unbounded state, and makes it
> fixed bounded. Which means printk() is now a O(1) algorithm.
						^^^
						O(logbuf)

and   O(logbuf) > watchdog_thresh   is totally possible. and there
is nothing super unlucky in having O(logbuf). limiting printk is the
right way to go, sure. but you limit it to the wrong thing. limiting
it to logbuf is not enough, especially given that logbuf size is
configurable via kernel param - it's a moving target. if one wants
printk to stop disappointing the watchdog then printk must learn to
respect watchdog's threshold.


https://marc.info/?l=linux-kernel&m=151444381104068


hence a small fix up

---

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 8882a4bf2a9e..4efa7542d84d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2341,6 +2341,14 @@ void console_unlock(void)
 
 		printk_safe_enter_irqsave(flags);
 		raw_spin_lock(&logbuf_lock);
+
+		if (log_next_seq - console_seq > 666) {
+			console_seq = log_next_seq;
+			raw_spin_unlock(&logbuf_lock);
+			printk_safe_exit_irqrestore(flags);
+			panic("you mad bro? this can softlockup your system! let me fix that for you");
+		}
+
 		if (seen_seq != log_next_seq) {
 			wake_klogd = true;
 			seen_seq = log_next_seq;

---

> The solution is simple, everyone at KS agreed with it, there should be
> no controversy here.

frankly speaking, that's not what I recall ;)


[..]
> My printk solution is solid, with no risk of regressions of current
> printk usages.

except that handing off a console_sem to atomic task when there
is   O(logbuf) > watchdog_thresh   is a regression, basically...
it is what it is.


> If anything, I'll pull theses patches myself, and push them to Linus
> directly

lovely.

	-ss