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kernel/acct.c: 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 32dc730860 ("get rid of timer in
kern/acct.c") in 2011, then another (correct) commit 795a2f22a8
("acct() should honour the limits from the very beginning") made the
problem more visible.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 32dc730860 ("get rid of timer in kern/acct.c")
Reported-by: TSUKADA Koutaro <[email protected]>
Suggested-by: TSUKADA Koutaro <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
Cc: Al Viro <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Oleg Nesterov 2018-01-04 16:17:49 -08:00 • committed by Linus Torvalds
commit 4d9570158b
1 changed files with 1 additions and 1 deletions
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2
kernel/acct.c
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@ -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 */