From: Paul Moore <paul@paul-moore.com>
To: Yang Yingliang <yangyingliang@huawei.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>,
Oleg Nesterov <oleg@redhat.com>,
john.johansen@canonical.com,
"chengjian (D)" <cj.chengjian@huawei.com>,
Kees Cook <keescook@chromium.org>, NeilBrown <neilb@suse.com>,
Anna Schumaker <Anna.Schumaker@netapp.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"Xiexiuqi (Xie XiuQi)" <xiexiuqi@huawei.com>,
Li Bin <huawei.libin@huawei.com>, Jason Yan <yanaijie@huawei.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Linux Security Module list
<linux-security-module@vger.kernel.org>,
SELinux <selinux@vger.kernel.org>
Subject: Re: kernel BUG at kernel/cred.c:434!
Date: Tue, 23 Apr 2019 16:18:49 -0400 [thread overview]
Message-ID: <CAHC9VhRitKcax43NL5JThKqsysyakmarYiC4qTQTkka5SNNHuw@mail.gmail.com> (raw)
In-Reply-To: <5CBE8FC4.8060400@huawei.com>
On Tue, Apr 23, 2019 at 12:08 AM Yang Yingliang
<yangyingliang@huawei.com> wrote:
> On 2019/4/23 3:48, Paul Moore wrote:
> > On Sat, Apr 20, 2019 at 3:39 AM Yang Yingliang <yangyingliang@huawei.com> wrote:
> >> I'm not sure you got my point.
> > I went back and looked at your previous emails again to try and
> > understand what you are talking about, and I'm a little confused by
> > some of the output ...
> >
> >> --- a/kernel/acct.c
> >> +++ b/kernel/acct.c
> >> @@ -481,6 +481,7 @@ static void do_acct_process(struct bsd_acct_struct
> >> *acct)
> >> flim = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
> >> current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
> >> /* Perform file operations on behalf of whoever enabled
> >> accounting */
> >> + pr_info("task:%px new cred:%px real cred:%px cred:%px\n",
> >> current, file->f_cred, current->real_cred, current->cred);
> >> orig_cred = override_creds(file->f_cred);
> > Okay, with this patch applied we should the task/cred info when
> > do_acct_process is called. Got it.
> >
> >> Messages:
> >> [ 56.643298] task:ffff88841a9595c0 new cred:ffff88841ae450c0 real
> >> cred:ffff88841ae450c0 cred:ffff88841ae450c0 //They are same.
> > Okay, it looks like do_acct_process() was called and f_cred,
> > real_cred, and cred are all the same.
>
> This is a original message, without patch applied.
The patch I am referring to is your pr_info patch (above). I'm not
talking about any other patches at the moment; I just want to
understand the example dmesg output you copied into your email.
With that in mind, the message above seems to indicate that
do_acct_process() has been invoked with f_cred, real_cred, and cred
all pointing to the same credentials struct, yes?
> >> [ 56.646609] Process accounting resumed
> > It looks like do_acct_process() has called check_free_space() now. So
> > far so good.
...
> >> [ 56.649943] task:ffff88841a9595c0 new cred:ffff88841ae450c0 real
> >> cred:ffff88841c96c300 cred:ffff88841ae450c0
> > Wait a minute ... why are we seeing this again? Looking at the task
> > pointer and the timestamp, this is the same task exiting and trying to
> > write to the accounting file, yes? This output is particularly
> > curious since it appears that real_cred has changed; where is this
> > happening?
>
> This is the message when the BUG_ON was triggered without applying any
> fix patch.
The only place in the code that generates this message is the bit of
code that you patches in using the pr_info() patch (above), yes? If
so, that would seem to indicate that the same task is calling
do_acct_process() twice, yes? I may be fundamentally misunderstanding
something about process accounting, but I though do_acct_process()
would only be called once for a given task - while it was exiting.
Yes, no?
> If we apply this patch "proc: prevent changes to overridden
> credentials", program
> runs like this:
I'd like to focus on understanding the dmesg output you shared first,
because it doesn't seem to make sense to me.
--
paul moore
www.paul-moore.com
prev parent reply other threads:[~2019-04-23 20:19 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <6e4428ca-3da1-a033-08f7-a51e57503989@huawei.com>
2019-04-12 15:28 ` kernel BUG at kernel/cred.c:434! Casey Schaufler
2019-04-15 13:43 ` Oleg Nesterov
2019-04-15 14:48 ` Paul Moore
2019-04-15 15:05 ` Oleg Nesterov
2019-04-15 16:20 ` Paul Moore
2019-04-16 3:40 ` Kees Cook
2019-04-16 14:46 ` chengjian (D)
2019-04-17 14:30 ` Paul Moore
2019-04-17 14:57 ` Oleg Nesterov
2019-04-17 15:39 ` Casey Schaufler
2019-04-17 15:40 ` Paul Moore
2019-04-17 16:27 ` Oleg Nesterov
2019-04-17 16:42 ` Casey Schaufler
2019-04-18 13:39 ` Stephen Smalley
2019-04-17 23:39 ` Paul Moore
2019-04-18 0:17 ` John Johansen
2019-04-18 0:24 ` Casey Schaufler
2019-04-18 2:49 ` Yang Yingliang
2019-04-19 2:04 ` Paul Moore
2019-04-19 2:34 ` Yang Yingliang
2019-04-19 13:24 ` Paul Moore
2019-04-19 14:34 ` Yang Yingliang
2019-04-19 16:13 ` Paul Moore
2019-04-20 7:38 ` Yang Yingliang
2019-04-22 19:48 ` Paul Moore
2019-04-23 4:08 ` Yang Yingliang
2019-04-23 20:18 ` Paul Moore [this message]
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