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 commit32dc730860
("get rid of timer in kern/acct.c") in 2011, then another (correct) commit795a2f22a8
("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:32dc730860
("get rid of timer in kern/acct.c") Reported-by: TSUKADA Koutaro <tsukada@ascade.co.jp> Suggested-by: TSUKADA Koutaro <tsukada@ascade.co.jp> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -102,7 +102,7 @@ static int check_free_space(struct bsd_acct_struct *acct)
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{
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struct kstatfs sbuf;
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if (time_is_before_jiffies(acct->needcheck))
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if (time_is_after_jiffies(acct->needcheck))
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goto out;
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/* May block */
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