Messages in this thread Patch in this message | | | Date | Wed, 13 Dec 2017 14:39:40 +0100 | From | Oleg Nesterov <> | Subject | [PATCH] acct: fix the acct->needcheck check in check_free_space() |
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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.
Fixes: 32dc73086015 ("get rid of timer in kern/acct.c") Cc: stable@vger.kernel.org Reported-by: TSUKADA Koutaro <tsukada@ascade.co.jp> Sugested-by: TSUKADA Koutaro <tsukada@ascade.co.jp> Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- kernel/acct.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/acct.c b/kernel/acct.c index 5b12843..bf90c09 100644 --- a/kernel/acct.c +++ b/kernel/acct.c @@ -101,7 +101,7 @@ 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 */ -- 2.5.0
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