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 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary 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-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 4d9570158b6260f449e317a5f9ed030c2504a615 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov <oleg@xxxxxxxxxx> 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@xxxxxxxxxx> 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@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> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/acct.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/acct.c +++ b/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 stable-queue which might be from oleg@xxxxxxxxxx are queue-4.14/kernel-acct.c-fix-the-acct-needcheck-check-in-check_free_space.patch