From 4d9570158b6260f449e317a5f9ed030c2504a615 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 4 Jan 2018 16:17:49 -0800 Subject: kernel/acct.c: fix the acct->needcheck check in check_free_space() 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 Suggested-by: TSUKADA Koutaro Signed-off-by: Oleg Nesterov Cc: Al Viro Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/acct.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/acct.c b/kernel/acct.c index d15c0ee4d955..addf7732fb56 100644 --- a/kernel/acct.c +++ b/kernel/acct.c @@ -102,7 +102,7 @@ static int check_free_space(struct bsd_acct_struct *acct) { struct kstatfs sbuf; - if (time_is_before_jiffies(acct->needcheck)) + if (time_is_after_jiffies(acct->needcheck)) goto out; /* May block */ -- cgit v1.2.3-59-g8ed1b