From: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
To: Christian Brauner <brauner@kernel.org>
Cc: 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>,
Miklos Szeredi <miklos@szeredi.hu>,
Amir Goldstein <amir73il@gmail.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, audit@vger.kernel.org,
linux-unionfs@vger.kernel.org
Subject: Re: [PATCH 06/16] capability: provide a helper for converting vfs_caps to xattr for userspace
Date: Fri, 1 Dec 2023 11:23:57 -0600 [thread overview]
Message-ID: <ZWoWrRgNDVRv6BTB@do-x1extreme> (raw)
In-Reply-To: <20231201-seide-famos-74e8c23ee2cc@brauner>
On Fri, Dec 01, 2023 at 05:57:35PM +0100, Christian Brauner wrote:
> On Wed, Nov 29, 2023 at 03:50:24PM -0600, Seth Forshee (DigitalOcean) wrote:
> > 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.
>
> Nice. Precise and clear, please just drop these bullet points into the
> kernel-doc of that function.
Will do.
> > +/**
> > + * 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-interrnal capability into the raw security.capability
> > + * xattr format. Includes permission checking and v2->v3 conversion as
> > + * appropriate.
> > + *
> > + * 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 0; on error, return < 0.
> > + */
> > +int vfs_caps_to_user_xattr(struct mnt_idmap *idmap,
> > + struct user_namespace *dest_userns,
> > + const struct vfs_caps *vfs_caps,
> > + void *data, int 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;
>
> For a v2 cap that we read vfs_caps->rootid will be vfsuid 0, right?
> So that means we're guaranteed to resolve that in the initial user
> namespace. IOW, rootid_owns_currentns() will indeed work with a pure v2
> cap. Ok. Just making sure that I understand that this won't cause
> EOVERFLOW for v2. But you would've likely seen that in tests right away.
Yes, that's all correct.
next prev parent reply other threads:[~2023-12-01 17:26 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-29 21:50 [PATCH 00/16] fs: use type-safe uid representation for filesystem capabilities Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 01/16] mnt_idmapping: split out core vfs[ug]id_t definitions into vfsid.h Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 02/16] mnt_idmapping: include cred.h Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 03/16] capability: rename cpu_vfs_cap_data to vfs_caps Seth Forshee (DigitalOcean)
2023-12-01 15:50 ` Christian Brauner
2023-12-05 21:25 ` [PATCH 3/16] " Paul Moore
2023-11-29 21:50 ` [PATCH 04/16] capability: use vfsuid_t for vfs_caps rootids Seth Forshee (DigitalOcean)
2023-12-05 21:25 ` [PATCH 4/16] " Paul Moore
2023-11-29 21:50 ` [PATCH 05/16] capability: provide helpers for converting between xattrs and vfs_caps Seth Forshee (DigitalOcean)
2023-12-01 16:41 ` Christian Brauner
2023-12-01 17:09 ` Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 06/16] capability: provide a helper for converting vfs_caps to xattr for userspace Seth Forshee (DigitalOcean)
2023-12-01 16:57 ` Christian Brauner
2023-12-01 17:23 ` Seth Forshee (DigitalOcean) [this message]
2023-11-29 21:50 ` [PATCH 07/16] fs: add inode operations to get/set/remove fscaps Seth Forshee (DigitalOcean)
2023-11-30 5:32 ` Amir Goldstein
2023-11-30 15:36 ` Seth Forshee (DigitalOcean)
2023-12-01 17:02 ` Christian Brauner
2023-12-01 17:38 ` Seth Forshee (DigitalOcean)
2023-12-05 11:50 ` Christian Brauner
2023-11-29 21:50 ` [PATCH 08/16] fs: add vfs_get_fscaps() Seth Forshee (DigitalOcean)
2023-12-01 17:09 ` Christian Brauner
2023-12-01 17:41 ` Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 09/16] fs: add vfs_set_fscaps() Seth Forshee (DigitalOcean)
2023-11-30 8:01 ` Amir Goldstein
2023-11-30 15:38 ` Seth Forshee (DigitalOcean)
2023-12-01 17:39 ` Christian Brauner
2023-12-01 18:18 ` Seth Forshee (DigitalOcean)
2023-12-07 14:42 ` Seth Forshee (DigitalOcean)
2023-12-10 16:41 ` Amir Goldstein
2023-11-29 21:50 ` [PATCH 10/16] fs: add vfs_remove_fscaps() Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 11/16] ovl: add fscaps handlers Seth Forshee (DigitalOcean)
2023-11-30 5:56 ` Amir Goldstein
2023-11-30 16:01 ` Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 12/16] ovl: use vfs_{get,set}_fscaps() for copy-up Seth Forshee (DigitalOcean)
2023-11-30 6:23 ` Amir Goldstein
2023-11-30 16:43 ` Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 13/16] fs: use vfs interfaces for capabilities xattrs Seth Forshee (DigitalOcean)
2023-11-29 21:50 ` [PATCH 14/16] commoncap: remove cap_inode_getsecurity() Seth Forshee (DigitalOcean)
2023-12-05 21:25 ` Paul Moore
2023-11-29 21:50 ` [PATCH 15/16] commoncap: use vfs fscaps interfaces for killpriv checks Seth Forshee (DigitalOcean)
2023-12-11 7:57 ` kernel test robot
2023-11-29 21:50 ` [PATCH 16/16] vfs: return -EOPNOTSUPP for fscaps from vfs_*xattr() Seth Forshee (DigitalOcean)
2023-11-30 6:10 ` Amir Goldstein
2023-11-30 16:40 ` Seth Forshee (DigitalOcean)
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