From: Oleg Nesterov <oleg@xxxxxxxxxx>
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@xxxxxxxxxx
Fixes: 32dc73086015 ("get rid of timer in kern/acct.c")
Reported-by: TSUKADA Koutaro <tsukada@xxxxxxxxxxxx>
Suggested-by: TSUKADA Koutaro <tsukada@xxxxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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 */
_