This is a note to let you know that I've just added the patch titled

kernel/acct.c: fix the acct->needcheck check in check_free_space()

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: kernel-acct.c-fix-the-acct-needcheck-check-in-check_free_space.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 4d9570158b6260f449e317a5f9ed030c2504a615 Mon Sep 17 00:00:00 2001

From: Oleg Nesterov oleg@redhat.com Date: Thu, 4 Jan 2018 16:17:49 -0800 Subject: kernel/acct.c: fix the acct->needcheck check in check_free_space()

From: Oleg Nesterov oleg@redhat.com

commit 4d9570158b6260f449e317a5f9ed030c2504a615 upstream.

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 Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- kernel/acct.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/acct.c +++ b/kernel/acct.c @@ -99,7 +99,7 @@ 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 stable-queue which might be from oleg@redhat.com are

queue-4.4/x86-kasan-write-protect-kasan-zero-shadow.patch queue-4.4/kernel-acct.c-fix-the-acct-needcheck-check-in-check_free_space.patch