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: Fri, 19 Apr 2019 12:13:29 -0400 [thread overview]
Message-ID: <CAHC9VhQqxL+LsK8YTD6PpTHaZsZ-PxAq3atdZKQcZLQZQH7t4g@mail.gmail.com> (raw)
In-Reply-To: <5CB9DC75.7010600@huawei.com>
On Fri, Apr 19, 2019 at 10:34 AM Yang Yingliang
<yangyingliang@huawei.com> wrote:
> On 2019/4/19 21:24, Paul Moore wrote:
> > On Thu, Apr 18, 2019 at 10:42 PM Yang Yingliang
> > <yangyingliang@huawei.com> wrote:
> >> On 2019/4/19 10:04, Paul Moore wrote:
> >>> On Wed, Apr 17, 2019 at 10:50 PM Yang Yingliang
> >>> <yangyingliang@huawei.com> wrote:
> >>>> On 2019/4/18 8:24, Casey Schaufler wrote:
> >>>>> On 4/17/2019 4:39 PM, Paul Moore wrote:
> >>>>>> Since it looks like all three LSMs which implement the setprocattr
> >>>>>> hook are vulnerable I'm open to the idea that proc_pid_attr_write() is
> >>>>>> a better choice for the cred != read_cred check, but I would want to
> >>>>>> make sure John and Casey are okay with that.
> >>>>>>
> >>>>>> John?
> >>>>>>
> >>>>>> Casey?
> >>>>> I'm fine with the change going into proc_pid_attr_write().
> >>>> The cred != real_cred checking is not enough.
> >>>>
> >>>> Consider this situation, when doing override, cred, real_cred and
> >>>> new_cred are all same:
> >>>>
> >>>> after override_creds() cred == real_cred == new1_cred
> >>> I'm sorry, you've lost me. After override_creds() returns
> >>> current->cred and current->real_cred are not going to be the same,
> >>> yes?
> >> It's possible the new cred is equal to current->real_cred and
> >> current->cred,
> >> so after overrides_creds(), they have the same value.
> > Both task_struct.cred and task_struct.real_cred are pointer values,
> > assuming that one uses prepare_creds() to allocate/initialize a new
> > cred struct for use with override_creds() then the newly created cred
> > should never be equal to task_struct.real_cred. Am I missing
> > something, or are you thinking of something else?
>
> In do_acct_process(), file->f_cred may equal to current->real_cred, I
> confirm
> it by adding some debug message in do_acct_process() like this:
I would expect that; real_cred is the task's objective DAC
credentials, so using it for f_cred makes sense.
What we are now talking about is the task's subjective credentials,
which can be overridden via override_creds(), and are what the LSMs
change via proc_pid_attr_write().
> --- 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);
--
paul moore
www.paul-moore.com
next prev parent reply other threads:[~2019-04-19 18:47 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 [this message]
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
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