From patchwork Sun Jun 9 10:43:35 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Jonathan Calmels X-Patchwork-Id: 13691208 Received: from flow3-smtp.messagingengine.com (flow3-smtp.messagingengine.com [103.168.172.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 92DFE24B5B; Sun, 9 Jun 2024 10:40:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=103.168.172.138 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717929626; cv=none; b=MlH8pasWbdjNKoMEAH0ByMjrYkFd1ywp0dhKoKwBZuQ+RVAgRAt2kp9kKfU8kcqQPqMFvJknuRfHFCdLONFf6hUM+55Wn/LooWVqUmukpc94WwLrDT3QxWvrplV1XY5Ne7DV/KN0rhWZACWSEh1Fv4vIW//j1/KQ3erTjbG12Ds= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717929626; c=relaxed/simple; bh=TRflIsPbASjR72yTWpx34CeYRaOCTbvPLNUnQ9bjQ6k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=cyHRtGU0UTWsa3c3klDSM7osXZp0bK5gpF8w9zmjdCDrC8VlDAtkCjbFejhVlyGV8gmJ08ujvoVmoGc2x4Xm6Fp+tUzYe90KfVqJkIf0fbWSVqIYf5gzDBRzGcE1vl8rWLCF5Mp96OqQz2rC7o6YTGWovaAE/B5P9ddr+ZP8zuc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=3xx0.net; spf=pass smtp.mailfrom=3xx0.net; dkim=pass (2048-bit key) header.d=3xx0.net header.i=@3xx0.net header.b=gsfwPULs; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b=UQOz4ItZ; arc=none smtp.client-ip=103.168.172.138 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=3xx0.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=3xx0.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=3xx0.net header.i=@3xx0.net header.b="gsfwPULs"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="UQOz4ItZ" Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailflow.nyi.internal (Postfix) with ESMTP id C56CA2001CA; Sun, 9 Jun 2024 06:40:23 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute4.internal (MEProxy); Sun, 09 Jun 2024 06:40:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=3xx0.net; h=cc :cc:content-transfer-encoding:content-type:content-type:date :date:from:from:in-reply-to:in-reply-to:message-id:mime-version :references:reply-to:subject:subject:to:to; s=fm1; t=1717929623; x=1717933223; bh=givYjoPOL2k44qEG2AAhLIKWw+SaQbnMN2v1JiAaofI=; b= gsfwPULsB5vGdh2divKYeX2pT9m7EhL7B8rHXxOxGrnjOluHppy8OC6V/mJFZ6qG RGZcSmXNOCxb86qNZyXSSrkCYSSNJ9fnL2PcxZexz4wNzkoDLbnKrmufOi8NZbxh Xa98Juv3S2ziLBs3ZYQD2XnvkNKcsZhPrQUJbcXDnTANkMHzxI/6MfevpAQntzGf Egvm14viEkR/hpYGwq/KECjvzN29akriG+vYyD0Br1E+t63mN4IVRmEv1tM2WvvO P7jQi1XAUOdoJL54p8/6s6eCb8Ob+1d1gFaOITzeWyhTtj8EB1Ed5dUJgUyZHsh7 z7FP+gbbFde7LylQsszfzw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:content-type:date:date:feedback-id:feedback-id :from:from:in-reply-to:in-reply-to:message-id:mime-version :references:reply-to:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm1; t=1717929623; x= 1717933223; bh=givYjoPOL2k44qEG2AAhLIKWw+SaQbnMN2v1JiAaofI=; b=U QOz4ItZeUl4PBUxODr3Q1h/fZXwI+Q1LDY2gPrf9FL0OOyk0CzxxbTIYafM5jirH 3aqh0gd+G3OxbxmS5+pVaTFKGlbuY3eDMUfWnIu6I5w2hY24b2PTQOiZuVmNhkuK buF6oUecCbOTJvDq1E2f/kWHwXJTxc99KNz/GzlZ1n8jggHlgeJF7bmb5Cc4vtxh 4vzpRpoH9t5M6rATh/++1ojrpJscOK2seRo2HShpcDLGqIpAOx/b+emrqla23Ope yPTI0OchbCaPiW9X1EfFPq2auSr8tfeQ8q2teol3k5kFk0wM016PJ/Yc6FbScqbY +ikf/xa1m4gqMjtItzmDw== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvledrfedtjedgfeduucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvvefufffkofgjfhggtgfgsehtkeertdertdejnecuhfhrohhmpeflohhn rghthhgrnhcuvegrlhhmvghlshcuoehjtggrlhhmvghlshesfeiggidtrdhnvghtqeenuc ggtffrrghtthgvrhhnpeeiueeukeeitddvheeiveeiiedvhfeljeeiteeggedtteeiueet iefhudfgvddvleenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfh hrohhmpehjtggrlhhmvghlshesfeiggidtrdhnvght X-ME-Proxy: Feedback-ID: i76614979:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Sun, 9 Jun 2024 06:40:19 -0400 (EDT) From: Jonathan Calmels To: brauner@kernel.org, ebiederm@xmission.com, Jonathan Corbet , Paul Moore , James Morris , "Serge E. Hallyn" , KP Singh , Matt Bobrowski , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , Stanislav Fomichev , Hao Luo , Jiri Olsa , Luis Chamberlain , Kees Cook , Joel Granados , John Johansen , David Howells , Jarkko Sakkinen , Stephen Smalley , Ondrej Mosnacek , Mykola Lysenko , Shuah Khan Cc: containers@lists.linux.dev, Jonathan Calmels , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-security-module@vger.kernel.org, bpf@vger.kernel.org, apparmor@lists.ubuntu.com, keyrings@vger.kernel.org, selinux@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v2 2/4] capabilities: Add securebit to restrict userns caps Date: Sun, 9 Jun 2024 03:43:35 -0700 Message-ID: <20240609104355.442002-3-jcalmels@3xx0.net> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240609104355.442002-1-jcalmels@3xx0.net> References: <20240609104355.442002-1-jcalmels@3xx0.net> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 This patch adds a new capability security bit designed to constrain a task’s userns capability set to its bounding set. The reason for this is twofold: - This serves as a quick and easy way to lock down a set of capabilities for a task, thus ensuring that any namespace it creates will never be more privileged than itself is. - This helps userspace transition to more secure defaults by not requiring specific logic for the userns capability set, or libcap support. Example: # capsh --secbits=$((1 << 8)) --drop=cap_sys_rawio -- \ -c 'unshare -r grep Cap /proc/self/status' CapInh: 0000000000000000 CapPrm: 000001fffffdffff CapEff: 000001fffffdffff CapBnd: 000001fffffdffff CapAmb: 0000000000000000 CapUNs: 000001fffffdffff Signed-off-by: Jonathan Calmels --- include/linux/securebits.h | 1 + include/uapi/linux/securebits.h | 11 ++++++++++- kernel/user_namespace.c | 5 +++++ 3 files changed, 16 insertions(+), 1 deletion(-) diff --git a/include/linux/securebits.h b/include/linux/securebits.h index 656528673983..5f9d85cd69c3 100644 --- a/include/linux/securebits.h +++ b/include/linux/securebits.h @@ -5,4 +5,5 @@ #include #define issecure(X) (issecure_mask(X) & current_cred_xxx(securebits)) +#define iscredsecure(cred, X) (issecure_mask(X) & cred->securebits) #endif /* !_LINUX_SECUREBITS_H */ diff --git a/include/uapi/linux/securebits.h b/include/uapi/linux/securebits.h index d6d98877ff1a..2da3f4be4531 100644 --- a/include/uapi/linux/securebits.h +++ b/include/uapi/linux/securebits.h @@ -52,10 +52,19 @@ #define SECBIT_NO_CAP_AMBIENT_RAISE_LOCKED \ (issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE_LOCKED)) +/* When set, user namespace capabilities are restricted to their parent's bounding set. */ +#define SECURE_USERNS_STRICT_CAPS 8 +#define SECURE_USERNS_STRICT_CAPS_LOCKED 9 /* make bit-8 immutable */ + +#define SECBIT_USERNS_STRICT_CAPS (issecure_mask(SECURE_USERNS_STRICT_CAPS)) +#define SECBIT_USERNS_STRICT_CAPS_LOCKED \ + (issecure_mask(SECURE_USERNS_STRICT_CAPS_LOCKED)) + #define SECURE_ALL_BITS (issecure_mask(SECURE_NOROOT) | \ issecure_mask(SECURE_NO_SETUID_FIXUP) | \ issecure_mask(SECURE_KEEP_CAPS) | \ - issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE)) + issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE) | \ + issecure_mask(SECURE_USERNS_STRICT_CAPS)) #define SECURE_ALL_LOCKS (SECURE_ALL_BITS << 1) #endif /* _UAPI_LINUX_SECUREBITS_H */ diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 7e624607330b..53848e2b68cd 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -10,6 +10,7 @@ #include #include #include +#include #include #include #include @@ -42,6 +43,10 @@ static void dec_user_namespaces(struct ucounts *ucounts) static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns) { + /* Limit userns capabilities to our parent's bounding set. */ + if (iscredsecure(cred, SECURE_USERNS_STRICT_CAPS)) + cred->cap_userns = cap_intersect(cred->cap_userns, cred->cap_bset); + /* Start with the capabilities defined in the userns set. */ cred->cap_bset = cred->cap_userns; cred->cap_permitted = cred->cap_userns;