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Message-ID: <lsq.1519831218.204548780@decadent.org.uk>
Date: Wed, 28 Feb 2018 15:20:18 +0000
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org, "Oleg Nesterov" <oleg@...hat.com>,
"TSUKADA Koutaro" <tsukada@...ade.co.jp>,
"Al Viro" <viro@...iv.linux.org.uk>,
"Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 169/254] kernel/acct.c: fix the acct->needcheck check
in check_free_space()
3.16.55-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Oleg Nesterov <oleg@...hat.com>
commit 4d9570158b6260f449e317a5f9ed030c2504a615 upstream.
As Tsukada explains, the time_is_before_jiffies(acct->needcheck) check
is very wrong, we need time_is_after_jiffies() to make sys_acct() work.
Ignoring the overflows, the code should "goto out" if needcheck >
jiffies, while currently it checks "needcheck < jiffies" and thus in the
likely case check_free_space() does nothing until jiffies overflow.
In particular this means that sys_acct() is simply broken, acct_on()
sets acct->needcheck = jiffies and expects that check_free_space()
should set acct->active = 1 after the free-space check, but this won't
happen if jiffies increments in between.
This was broken by commit 32dc73086015 ("get rid of timer in
kern/acct.c") in 2011, then another (correct) commit 795a2f22a8ea
("acct() should honour the limits from the very beginning") made the
problem more visible.
Link: http://lkml.kernel.org/r/20171213133940.GA6554@redhat.com
Fixes: 32dc73086015 ("get rid of timer in kern/acct.c")
Reported-by: TSUKADA Koutaro <tsukada@...ade.co.jp>
Suggested-by: TSUKADA Koutaro <tsukada@...ade.co.jp>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
kernel/acct.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -107,7 +107,7 @@ static int check_free_space(struct bsd_a
spin_lock(&acct_lock);
res = acct->active;
- if (!file || time_is_before_jiffies(acct->needcheck))
+ if (!file || time_is_after_jiffies(acct->needcheck))
goto out;
spin_unlock(&acct_lock);
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