From: Oleg Nesterov oleg@redhat.com 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 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 ---
kernel/acct.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN kernel/acct.c~acct-fix-the-acct-needcheck-check-in-check_free_space kernel/acct.c --- a/kernel/acct.c~acct-fix-the-acct-needcheck-check-in-check_free_space +++ a/kernel/acct.c @@ -102,7 +102,7 @@ static int check_free_space(struct bsd_a { struct kstatfs sbuf;
- if (time_is_before_jiffies(acct->needcheck)) + if (time_is_after_jiffies(acct->needcheck)) goto out;
/* May block */ _