+ acct-fix-the-acct-needcheck-check-in-check_free_space.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: kernel/acct.c: fix the acct->needcheck check in check_free_space()
has been added to the -mm tree.  Its filename is
     acct-fix-the-acct-needcheck-check-in-check_free_space.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/acct-fix-the-acct-needcheck-check-in-check_free_space.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/acct-fix-the-acct-needcheck-check-in-check_free_space.patch

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------------------------------------------------------
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 */
_

Patches currently in -mm which might be from oleg@redhat.com are

acct-fix-the-acct-needcheck-check-in-check_free_space.patch