From: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
To: Christian Brauner <brauner@kernel.org>,
Seth Forshee <sforshee@kernel.org>,
Serge Hallyn <serge@hallyn.com>,
Paul Moore <paul@paul-moore.com>, Eric Paris <eparis@redhat.com>,
James Morris <jmorris@namei.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Jan Kara <jack@suse.cz>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
Ondrej Mosnacek <omosnace@redhat.com>,
Casey Schaufler <casey@schaufler-ca.com>,
Mimi Zohar <zohar@linux.ibm.com>,
Roberto Sassu <roberto.sassu@huawei.com>,
Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
Eric Snowberg <eric.snowberg@oracle.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Jonathan Corbet <corbet@lwn.net>,
Miklos Szeredi <miklos@szeredi.hu>,
Amir Goldstein <amir73il@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, audit@vger.kernel.org,
selinux@vger.kernel.org, linux-integrity@vger.kernel.org,
linux-doc@vger.kernel.org, linux-unionfs@vger.kernel.org
Subject: [PATCH v2 07/25] capability: provide a helper for converting vfs_caps to xattr for userspace
Date: Wed, 21 Feb 2024 15:24:38 -0600 [thread overview]
Message-ID: <20240221-idmap-fscap-refactor-v2-7-3039364623bd@kernel.org> (raw)
In-Reply-To: <20240221-idmap-fscap-refactor-v2-0-3039364623bd@kernel.org>
cap_inode_getsecurity() implements a handful of policies for capability
xattrs read by userspace:
- It returns EINVAL if the on-disk capability is in v1 format.
- It masks off all bits in magic_etc except for the version and
VFS_CAP_FLAGS_EFFECTIVE.
- v3 capabilities are converted to v2 format if the rootid returned to
userspace would be 0 or if the rootid corresponds to root in an
ancestor user namespace.
- It returns EOVERFLOW for a v3 capability whose rootid does not map to
a valid id in current_user_ns() or to root in an ancestor namespace.
These policies must be maintained when converting vfs_caps to an xattr
for userspace. Provide a vfs_caps_to_user_xattr() helper which will
enforce these policies.
Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
---
include/linux/capability.h | 4 +++
security/commoncap.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 82 insertions(+)
diff --git a/include/linux/capability.h b/include/linux/capability.h
index a0893ac4664b..eb06d7c6224b 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -218,6 +218,10 @@ ssize_t vfs_caps_to_xattr(struct mnt_idmap *idmap,
struct user_namespace *dest_userns,
const struct vfs_caps *vfs_caps,
void *data, size_t size);
+ssize_t vfs_caps_to_user_xattr(struct mnt_idmap *idmap,
+ struct user_namespace *dest_userns,
+ const struct vfs_caps *vfs_caps,
+ void *data, size_t size);
/* audit system wants to get cap info from files as well */
int get_vfs_caps_from_disk(struct mnt_idmap *idmap,
diff --git a/security/commoncap.c b/security/commoncap.c
index 7531c9634997..289530e58c37 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -791,6 +791,84 @@ ssize_t vfs_caps_to_xattr(struct mnt_idmap *idmap,
return ret;
}
+/**
+ * vfs_caps_to_user_xattr - convert vfs_caps to caps xattr for userspace
+ *
+ * @idmap: idmap of the mount the inode was found from
+ * @dest_userns: user namespace for ids in xattr data
+ * @vfs_caps: source vfs_caps data
+ * @data: destination buffer for rax xattr caps data
+ * @size: size of the @data buffer
+ *
+ * Converts a kernel-internal capability into the raw security.capability
+ * xattr format. Implements the following policies required for fscaps
+ * returned to userspace:
+ *
+ * - Returns -EINVAL if the on-disk capability is in v1 format.
+ * - Masks off all bits in magic_etc except for the version and
+ * VFS_CAP_FLAGS_EFFECTIVE.
+ * - Converts v3 capabilities to v2 format if the rootid returned to
+ * userspace would be 0 or if the rootid corresponds to root in an
+ * ancestor user namespace.
+ * - Returns EOVERFLOW for a v3 capability whose rootid does not map to a
+ * valid id in current_user_ns() or to root in an ancestor namespace.
+ *
+ * If the xattr is being read or written through an idmapped mount the
+ * idmap of the vfsmount must be passed through @idmap. This function
+ * will then take care to map the rootid according to @idmap.
+ *
+ * Return: On success, return the size of the xattr data. On error,
+ * return < 0.
+ */
+ssize_t vfs_caps_to_user_xattr(struct mnt_idmap *idmap,
+ struct user_namespace *dest_userns,
+ const struct vfs_caps *vfs_caps,
+ void *data, size_t size)
+{
+ struct vfs_ns_cap_data *ns_caps = data;
+ bool is_v3;
+ u32 magic;
+
+ /* Preserve previous behavior of returning EINVAL for v1 caps */
+ if ((vfs_caps->magic_etc & VFS_CAP_REVISION_MASK) == VFS_CAP_REVISION_1)
+ return -EINVAL;
+
+ size = __vfs_caps_to_xattr(idmap, dest_userns, vfs_caps, data, size);
+ if (size < 0)
+ return size;
+
+ magic = vfs_caps->magic_etc &
+ (VFS_CAP_REVISION_MASK | VFS_CAP_FLAGS_EFFECTIVE);
+ ns_caps->magic_etc = cpu_to_le32(magic);
+
+ /*
+ * If this is a v3 capability with a valid, non-zero rootid, return
+ * the v3 capability to userspace. A v3 capability with a rootid of
+ * 0 will be converted to a v2 capability below for compatibility
+ * with old userspace.
+ */
+ is_v3 = (vfs_caps->magic_etc & VFS_CAP_REVISION_MASK) == VFS_CAP_REVISION_3;
+ if (is_v3) {
+ uid_t rootid = le32_to_cpu(ns_caps->rootid);
+ if (rootid != (uid_t)-1 && rootid != (uid_t)0)
+ return size;
+ }
+
+ if (!rootid_owns_currentns(vfs_caps->rootid))
+ return -EOVERFLOW;
+
+ /* This comes from a parent namespace. Return as a v2 capability. */
+ if (is_v3) {
+ magic = VFS_CAP_REVISION_2 |
+ (vfs_caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE);
+ ns_caps->magic_etc = cpu_to_le32(magic);
+ ns_caps->rootid = cpu_to_le32(0);
+ size = XATTR_CAPS_SZ_2;
+ }
+
+ return size;
+}
+
/**
* get_vfs_caps_from_disk - retrieve vfs caps from disk
*
--
2.43.0
next prev parent reply other threads:[~2024-02-21 21:25 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-21 21:24 [PATCH v2 00/25] fs: use type-safe uid representation for filesystem capabilities Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 01/25] mnt_idmapping: split out core vfs[ug]id_t definitions into vfsid.h Seth Forshee (DigitalOcean)
2024-02-22 14:09 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 02/25] mnt_idmapping: include cred.h Seth Forshee (DigitalOcean)
2024-02-22 14:12 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 03/25] capability: add static asserts for comapatibility of vfs_cap_data and vfs_ns_cap_data Seth Forshee (DigitalOcean)
2024-02-22 14:23 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 04/25] capability: rename cpu_vfs_cap_data to vfs_caps Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 05/25] capability: use vfsuid_t for vfs_caps rootids Seth Forshee (DigitalOcean)
2024-02-22 14:25 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 06/25] capability: provide helpers for converting between xattrs and vfs_caps Seth Forshee (DigitalOcean)
2024-02-22 15:20 ` Christian Brauner
2024-02-22 15:38 ` Seth Forshee (DigitalOcean)
2024-02-23 8:08 ` Christian Brauner
2024-03-01 16:30 ` Roberto Sassu
2024-03-01 19:00 ` Seth Forshee (DigitalOcean)
2024-03-04 8:33 ` Roberto Sassu
2024-03-04 14:24 ` Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` Seth Forshee (DigitalOcean) [this message]
2024-02-22 15:22 ` [PATCH v2 07/25] capability: provide a helper for converting vfs_caps to xattr for userspace Christian Brauner
2024-02-21 21:24 ` [PATCH v2 08/25] xattr: add is_fscaps_xattr() helper Seth Forshee (DigitalOcean)
2024-02-23 8:09 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 09/25] commoncap: use is_fscaps_xattr() Seth Forshee (DigitalOcean)
2024-02-23 8:10 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 10/25] xattr: " Seth Forshee (DigitalOcean)
2024-02-23 8:10 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 11/25] security: add hooks for set/get/remove of fscaps Seth Forshee (DigitalOcean)
2024-02-21 23:31 ` Paul Moore
2024-02-22 0:07 ` Seth Forshee (DigitalOcean)
2024-02-23 8:23 ` Christian Brauner
2024-03-01 15:59 ` Roberto Sassu
2024-03-01 18:50 ` Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 12/25] selinux: add hooks for fscaps operations Seth Forshee (DigitalOcean)
2024-02-21 23:38 ` Paul Moore
2024-02-22 0:10 ` Seth Forshee (DigitalOcean)
2024-02-22 0:19 ` Paul Moore
2024-02-22 0:28 ` Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 13/25] smack: " Seth Forshee (DigitalOcean)
2024-02-21 22:52 ` Casey Schaufler
2024-02-22 0:11 ` Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 14/25] evm: add support for fscaps security hooks Seth Forshee (DigitalOcean)
2024-03-01 9:19 ` Roberto Sassu
2024-03-01 12:54 ` Christian Brauner
2024-03-01 13:19 ` Roberto Sassu
2024-03-01 13:39 ` Christian Brauner
2024-03-01 14:39 ` Seth Forshee (DigitalOcean)
2024-03-01 15:04 ` Roberto Sassu
2024-03-04 15:01 ` Roberto Sassu
2024-02-21 21:24 ` [PATCH v2 15/25] security: call evm fscaps hooks from generic " Seth Forshee (DigitalOcean)
2024-02-21 23:43 ` Paul Moore
2024-02-22 0:20 ` Seth Forshee (DigitalOcean)
2024-02-22 0:37 ` Paul Moore
2024-02-21 21:24 ` [PATCH v2 16/25] fs: add inode operations to get/set/remove fscaps Seth Forshee (DigitalOcean)
2024-02-23 8:25 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 17/25] fs: add vfs_get_fscaps() Seth Forshee (DigitalOcean)
2024-02-23 8:28 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 18/25] fs: add vfs_set_fscaps() Seth Forshee (DigitalOcean)
2024-02-23 8:38 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 19/25] fs: add vfs_remove_fscaps() Seth Forshee (DigitalOcean)
2024-02-23 8:40 ` Christian Brauner
2024-02-21 21:24 ` [PATCH v2 20/25] ovl: add fscaps handlers Seth Forshee (DigitalOcean)
2024-02-23 9:04 ` Christian Brauner
2024-02-27 13:28 ` Amir Goldstein
2024-02-27 14:57 ` Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 21/25] ovl: use vfs_{get,set}_fscaps() for copy-up Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 22/25] fs: use vfs interfaces for capabilities xattrs Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 23/25] commoncap: remove cap_inode_getsecurity() Seth Forshee (DigitalOcean)
2024-02-21 21:24 ` [PATCH v2 24/25] commoncap: use vfs fscaps interfaces Seth Forshee (DigitalOcean)
2024-03-04 10:19 ` Roberto Sassu
2024-03-04 15:31 ` Seth Forshee (DigitalOcean)
2024-03-04 16:17 ` Roberto Sassu
2024-03-04 16:56 ` Seth Forshee (DigitalOcean)
2024-03-05 9:12 ` Christian Brauner
2024-03-05 12:46 ` Roberto Sassu
2024-03-05 16:26 ` Christian Brauner
2024-03-05 16:35 ` Roberto Sassu
2024-03-05 17:03 ` Seth Forshee (DigitalOcean)
2024-03-05 17:08 ` Roberto Sassu
2024-03-05 17:11 ` Roberto Sassu
2024-03-05 20:17 ` Seth Forshee (DigitalOcean)
2024-03-06 8:30 ` Roberto Sassu
2024-03-06 2:17 ` Mimi Zohar
2024-03-06 8:25 ` Roberto Sassu
2024-03-06 12:56 ` Mimi Zohar
2024-02-21 21:24 ` [PATCH v2 25/25] vfs: return -EOPNOTSUPP for fscaps from vfs_*xattr() Seth Forshee (DigitalOcean)
2024-02-22 15:27 ` [PATCH v2 00/25] fs: use type-safe uid representation for filesystem capabilities Christian Brauner
2024-02-22 16:28 ` Seth Forshee (DigitalOcean)
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