From: Yang Yingliang <yangyingliang@huawei.com>
To: Paul Moore <paul@paul-moore.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>, <yangyingliang@huawei.com>
Subject: Re: kernel BUG at kernel/cred.c:434!
Date: Tue, 23 Apr 2019 12:08:36 +0800 [thread overview]
Message-ID: <5CBE8FC4.8060400@huawei.com> (raw)
In-Reply-To: <CAHC9VhSZBh8B+1CPM=PdLdbSFq1ba1ffuOJTgnzE5oBLXUEDxQ@mail.gmail.com>
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.
>
>> [ 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.
If we apply this patch "proc: prevent changes to overridden
credentials", program
runs like this:
1. As print message shows, before overriden, the pointer has the
following value:
real_cread=cred=0xffff88841ae450c0, f_cred=0xffff88841ae450c0
override_creds() is called in do_acct_process():
...
/* Perform file operations on behalf of whoever enabled accounting */
orig_cred = override_creds(file->f_cred);
...
2. After override_creds(), if (current_cred() != current_real_cred()) is
not work here,
we will call commit_creds() in security_setprocattr().
...
/* Prevent changes to overridden credentials. */
if (current_cred() != current_real_cred()) {
rcu_read_unlock();
return -EBUSY;
}
...
3. After commit_creds(), we have new cred and real_cred.
security_setprocattr() //commit_creds is called here
4. revert_creds() is called in in do_acct_process(), the cred
is reverted to the old value(0xffff88841ae450c0)
...
current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
revert_creds(orig_cred);
5. After reverting, cred and real_cred are not equal.
If it has a risk to trigger the BUG_ON, when doing another
commit_creds() ?
next prev parent reply other threads:[~2019-04-23 4:08 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 [this message]
2019-04-23 20:18 ` Paul Moore
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