From: CGEL <cgel.zte@gmail.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: peterz@infradead.org, tglx@linutronix.de,
linux-kernel@vger.kernel.org,
Ran Xiaokai <ran.xiaokai@zte.com.cn>,
James Morris <jamorris@linux.microsoft.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Kees Cook <keescook@chromium.org>, NeilBrown <neilb@suse.de>
Subject: Re: [PATCH] set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds
Date: Tue, 3 Aug 2021 03:03:54 -0700 [thread overview]
Message-ID: <20210803100354.GA607722@www> (raw)
In-Reply-To: <20210730082329.GA544980@www>
On Fri, Jul 30, 2021 at 01:23:31AM -0700, CGEL wrote:
> On Wed, Jul 28, 2021 at 01:59:30PM +0200, Christian Brauner wrote:
> > [Ccing a few people that did the PF_NPROC_EXCEEDED changes]
> >
> >
> > Hey Cgel,
> > Hey Ran,
> >
> > The gist seems to me that this code wants to make sure that a program
> > can't successfully exec if it has gone through a set*id() transition
> > while exceeding its RLIMIT_NPROC.
> >
> > But I agree that the semantics here are a bit strange.
> >
> > Iicu, a capable but non-INIT_USER caller getting PF_NPROC_EXCEEDED set
> > during a set*id() transition wouldn't be able to exec right away if they
> > still exceed their RLIMIT_NPROC at the time of exec. So their exec would
> > fail in fs/exec.c:
> >
> > if ((current->flags & PF_NPROC_EXCEEDED) &&
> > is_ucounts_overlimit(current_ucounts(), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
> > retval = -EAGAIN;
> > goto out_ret;
> > }
> >
> > However, if the caller were to fork() right after the set*id()
> > transition but before the exec while still exceeding their RLIMIT_NPROC
> > then they would get PF_NPROC_EXCEEDED cleared (while the child would
> > inherit it):
> >
> > retval = -EAGAIN;
> > if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
> > if (p->real_cred->user != INIT_USER &&
> > !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
> > goto bad_fork_free;
> > }
> > current->flags &= ~PF_NPROC_EXCEEDED;
> >
> > which means a subsequent exec by the capable caller would now succeed
> > even though they could still exceed their RLIMIT_NPROC limit.
> >
> > So at first glance, it seems that set_user() should probably get the
> > same check as it can be circumvented today unless I misunderstand the
> > original motivation.
> >
> > Christian
>
> Hi Christian,
>
> I think i didn't give enough information in the commit message.
> When switch to a capable but non-INIT_SUER and the RLIMIT_NPROC limit already exceeded,
> and calls these funcs:
> 1. set_xxuid()->exec()
> ---> fail
> 2. set_xxuid()->fork()->exec()
> ---> success
> Kernel should have the same behavior to uer space.
> Also i think non init_user CAN exceed the limit when with proper capability,
> so in the patch, set_user() clear PF_NPROC_EXCEEDED flag if capable()
> returns true.
Hi, Christian
Do you have any further comments on this patch?
is there anything i did not give enough infomation ?
next prev parent reply other threads:[~2021-08-03 10:03 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-28 7:26 [PATCH] set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds cgel.zte
2021-07-28 11:59 ` Christian Brauner
2021-07-30 8:23 ` CGEL
2021-08-03 10:03 ` CGEL [this message]
2021-08-03 14:07 ` Christian Brauner
2021-09-07 21:30 ` Solar Designer
2021-09-08 10:24 ` Solar Designer
2021-09-13 10:01 ` Christian Brauner
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