From: "Eric W. Biederman" <ebiederm@xmission.com>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org,
"Linux API" <linux-api@vger.kernel.org>,
"Etienne Dechamps" <etienne@edechamps.fr>,
"Alexey Gladkov" <legion@kernel.org>,
"Shuah Khan" <shuah@kernel.org>,
"Christian Brauner" <brauner@kernel.org>,
"Solar Designer" <solar@openwall.com>,
"Ran Xiaokai" <ran.xiaokai@zte.com.cn>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
"Linux Containers" <containers@lists.linux-foundation.org>,
"Michal Koutný" <mkoutny@suse.com>,
"Security Officers" <security@kernel.org>,
"Neil Brown" <neilb@cse.unsw.edu.au>, NeilBrown <neilb@suse.de>,
"Serge E. Hallyn" <serge@hallyn.com>,
"Jann Horn" <jannh@google.com>,
"Andy Lutomirski" <luto@kernel.org>, "Willy Tarreau" <w@1wt.eu>,
"Linus Torvalds" <linus@torvalds.org>
Subject: Re: [PATCH] ucounts: Fix systemd LimigtNPROC with private users regression
Date: Thu, 24 Feb 2022 18:29:24 -0600 [thread overview]
Message-ID: <87y21zhjq3.fsf@email.froward.int.ebiederm.org> (raw)
In-Reply-To: <202202240826.E31BADF@keescook> (Kees Cook's message of "Thu, 24 Feb 2022 08:28:41 -0800")
Kees Cook <keescook@chromium.org> writes:
> typo: Subject's LimigtNPROC -> LimitNPROC
>
> On Thu, Feb 24, 2022 at 09:41:44AM -0600, Eric W. Biederman wrote:
>>
>> Long story short recursively enforcing RLIMIT_NPROC when it is not
>> enforced on the process that creates a new user namespace, causes
>> currently working code to fail. There is no reason to enforce
>> RLIMIT_NPROC recursively when we don't enforce it normally so update
>> the code to detect this case.
>>
>> I would like to simply use capable(CAP_SYS_RESOURCE) to detect when
>> RLIMIT_NPROC is not enforced upon the caller. Unfortunately because
>> RLIMIT_NPROC is charged and checked for enforcement based upon the
>> real uid, using capable() wich is euid based is inconsistent with reality.
>
> typo: wich -> which
Ahh... Typos.
>> Come as close as possible to testing for capable(CAP_SYS_RESOURCE) by
>> testing for when the real uid would match the conditions when
>> CAP_SYS_RESOURCE would be present if the real uid was the effective
>> uid.
>>
>> Reported-by: Etienne Dechamps <etienne@edechamps.fr>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215596
>> Link: https://lkml.kernel.org/r/e9589141-cfeb-90cd-2d0e-83a62787239a@edechamps.fr
>> Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
>> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>> ---
>>
>> The previous conversation has given me enough clarity that I can see
>> which tests I am comfortable with use for this pending regression fix.
>>
>> I have tested this and it works for me. Does anyone have any concerns
>> with this change?
>
> I'd really love some kind of selftest that exercises the edge cases; do
> you have your tests in some form that could be converted?
>
> But otherwise, yes, this looks like the best option here.
Let's start with Michal Koutný tests. I keep forgetting to look at
them. This cold has really been kicking my butt.
For this issue the test case was a systemd unit file. Which is simple
and demonstrates the real-world regression but not really minimal in the
way a kernel selftest should be.
> Reviewed-by: Kees Cook <keescook@chromium.org>
>
>>
>> kernel/user_namespace.c | 14 +++++++++++++-
>> 1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
>> index 6b2e3ca7ee99..5481ba44a8d6 100644
>> --- a/kernel/user_namespace.c
>> +++ b/kernel/user_namespace.c
>> @@ -58,6 +58,18 @@ static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
>> cred->user_ns = user_ns;
>> }
>>
>> +static unsigned long enforced_nproc_rlimit(void)
>> +{
>> + unsigned long limit = RLIM_INFINITY;
>> +
>> + /* Is RLIMIT_NPROC currently enforced? */
>> + if (!uid_eq(current_uid(), GLOBAL_ROOT_UID) ||
>> + (current_user_ns() != &init_user_ns))
>> + limit = rlimit(RLIMIT_NPROC);
>> +
>> + return limit;
>> +}
>> +
>> /*
>> * Create a new user namespace, deriving the creator from the user in the
>> * passed credentials, and replacing that user with the new root user for the
>> @@ -122,7 +134,7 @@ int create_user_ns(struct cred *new)
>> for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++) {
>> ns->ucount_max[i] = INT_MAX;
>> }
>> - set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC));
>> + set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_NPROC, enforced_nproc_rlimit());
>> set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MSGQUEUE, rlimit(RLIMIT_MSGQUEUE));
>> set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_SIGPENDING, rlimit(RLIMIT_SIGPENDING));
>> set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MEMLOCK, rlimit(RLIMIT_MEMLOCK));
>> --
>> 2.29.2
>>
Eric
next prev parent reply other threads:[~2022-02-25 0:29 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 12:17 [RFC PATCH 0/6] RLIMIT_NPROC in ucounts fixups Michal Koutný
2022-02-07 12:17 ` [RFC PATCH 1/6] set_user: Perform RLIMIT_NPROC capability check against new user credentials Michal Koutný
2022-02-10 1:14 ` Solar Designer
2022-02-10 1:57 ` Eric W. Biederman
2022-02-11 20:32 ` Eric W. Biederman
2022-02-12 22:14 ` Solar Designer
2022-02-15 11:55 ` Michal Koutný
2022-02-07 12:17 ` [RFC PATCH 2/6] set*uid: Check RLIMIT_PROC against new credentials Michal Koutný
2022-02-07 12:17 ` [RFC PATCH 3/6] cred: Count tasks by their real uid into RLIMIT_NPROC Michal Koutný
2022-02-07 12:17 ` [RFC PATCH 4/6] ucounts: Allow root to override RLIMIT_NPROC Michal Koutný
2022-02-10 0:21 ` Eric W. Biederman
2022-02-07 12:17 ` [RFC PATCH 5/6] selftests: Challenge RLIMIT_NPROC in user namespaces Michal Koutný
2022-02-10 1:22 ` Shuah Khan
2022-02-15 9:45 ` Michal Koutný
2022-02-07 12:18 ` [RFC PATCH 6/6] selftests: Test RLIMIT_NPROC in clone-created " Michal Koutný
2022-02-10 1:25 ` Shuah Khan
2022-02-15 9:34 ` Michal Koutný
2022-02-08 13:54 ` [RFC PATCH 0/6] RLIMIT_NPROC in ucounts fixups Eric W. Biederman
2022-02-11 2:01 ` [PATCH 0/8] ucounts: RLIMIT_NPROC fixes Eric W. Biederman
2022-02-11 2:13 ` [PATCH 1/8] ucounts: Fix RLIMIT_NPROC regression Eric W. Biederman
2022-02-14 18:37 ` Michal Koutný
2022-02-16 15:22 ` Eric W. Biederman
2022-02-11 2:13 ` [PATCH 2/8] ucounts: Fix set_cred_ucounts Eric W. Biederman
2022-02-15 11:10 ` Michal Koutný
2022-02-11 2:13 ` [PATCH 3/8] ucounts: Fix and simplify RLIMIT_NPROC handling during setuid()+execve Eric W. Biederman
2022-02-12 23:17 ` Solar Designer
2022-02-14 15:10 ` Eric W. Biederman
2022-02-14 17:43 ` Eric W. Biederman
2022-02-15 10:25 ` Michal Koutný
2022-02-16 15:35 ` Eric W. Biederman
2022-02-11 2:13 ` [PATCH 4/8] ucounts: Only except the root user in init_user_ns from RLIMIT_NPROC Eric W. Biederman
2022-02-15 10:54 ` Michal Koutný
2022-02-16 15:41 ` Eric W. Biederman
2022-02-11 2:13 ` [PATCH 5/8] ucounts: Handle wrapping in is_ucounts_overlimit Eric W. Biederman
2022-02-12 22:36 ` Solar Designer
2022-02-14 15:23 ` Eric W. Biederman
2022-02-14 15:23 ` Eric W. Biederman
2022-02-15 11:25 ` Michal Koutný
2022-02-14 17:16 ` David Laight
2022-02-11 2:13 ` [PATCH 6/8] ucounts: Handle inc_rlimit_ucounts wrapping in fork Eric W. Biederman
2022-02-11 11:34 ` Alexey Gladkov
2022-02-11 17:50 ` Eric W. Biederman
2022-02-11 18:32 ` Shuah Khan
2022-02-11 18:40 ` Alexey Gladkov
2022-02-11 19:56 ` Eric W. Biederman
2022-02-11 2:13 ` [PATCH 7/8] rlimit: For RLIMIT_NPROC test the child not the parent for capabilites Eric W. Biederman
2022-02-11 2:13 ` [PATCH 8/8] ucounts: Use the same code to enforce RLIMIT_NPROC in fork and exec Eric W. Biederman
2022-02-11 18:22 ` [PATCH 0/8] ucounts: RLIMIT_NPROC fixes Shuah Khan
2022-02-11 19:23 ` Eric W. Biederman
2022-02-15 11:37 ` Michal Koutný
2022-02-16 15:56 ` [PATCH v2 0/5] " Eric W. Biederman
2022-02-16 15:58 ` [PATCH v2 1/5] rlimit: Fix RLIMIT_NPROC enforcement failure caused by capability calls in set_user Eric W. Biederman
2022-02-16 17:42 ` Solar Designer
2022-02-16 15:58 ` [PATCH v2 2/5] ucounts: Enforce RLIMIT_NPROC not RLIMIT_NPROC+1 Eric W. Biederman
2022-02-16 15:58 ` [PATCH v2 3/5] ucounts: Base set_cred_ucounts changes on the real user Eric W. Biederman
2022-02-16 15:58 ` [PATCH v2 4/5] ucounts: Move RLIMIT_NPROC handling after set_user Eric W. Biederman
2022-02-16 15:58 ` [PATCH v2 5/5] ucounts: Handle wrapping in is_ucounts_overlimit Eric W. Biederman
2022-02-16 17:28 ` Shuah Khan
2022-02-18 15:34 ` [GIT PULL] ucounts: RLIMIT_NPROC fixes for v5.17 Eric W. Biederman
2022-02-20 19:05 ` pr-tracker-bot
2022-03-03 0:12 ` [GIT PULL] ucounts: Regression fix " Eric W. Biederman
2022-03-03 0:30 ` pr-tracker-bot
2022-02-12 15:32 ` [RFC PATCH 0/6] RLIMIT_NPROC in ucounts fixups Etienne Dechamps
2022-02-15 10:11 ` Michal Koutný
2022-02-23 0:57 ` Eric W. Biederman
2022-02-23 18:00 ` How should rlimits, suid exec, and capabilities interact? Eric W. Biederman
2022-02-23 19:44 ` Andy Lutomirski
2022-02-23 21:28 ` Willy Tarreau
2022-02-23 19:50 ` Linus Torvalds
2022-02-24 1:24 ` Eric W. Biederman
2022-02-24 1:41 ` Linus Torvalds
2022-02-24 2:12 ` Eric W. Biederman
2022-02-24 15:41 ` [PATCH] ucounts: Fix systemd LimigtNPROC with private users regression Eric W. Biederman
2022-02-24 16:28 ` Kees Cook
2022-02-24 18:53 ` Michal Koutný
2022-02-25 0:29 ` Eric W. Biederman [this message]
2022-02-24 3:00 ` How should rlimits, suid exec, and capabilities interact? David Laight
2022-02-24 1:32 ` Eric W. Biederman
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