Date:   Tue, 13 Jun 2017 18:42:14 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Masami Ichikawa <masami256@...il.com>,
        containers@...ts.linux-foundation.org, lkp@...org,
        xiaolong.ye@...el.com, LKML <linux-kernel@...r.kernel.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4] Introduce v3 namespaced file capabilities

Quoting Stefan Berger (stefanb@...ux.vnet.ibm.com):
> On 05/08/2017 02:11 PM, Serge E. Hallyn wrote:
> >Root in a non-initial user ns cannot be trusted to write a traditional
> >security.capability xattr.  If it were allowed to do so, then any
> >unprivileged user on the host could map his own uid to root in a private
> >namespace, write the xattr, and execute the file with privilege on the
> >host.
> >
> >However supporting file capabilities in a user namespace is very
> >desirable.  Not doing so means that any programs designed to run with
> >limited privilege must continue to support other methods of gaining and
> >dropping privilege.  For instance a program installer must detect
> >whether file capabilities can be assigned, and assign them if so but set
> >setuid-root otherwise.  The program in turn must know how to drop
> >partial capabilities, and do so only if setuid-root.
> 
> Hi Serge,
> 
> 
>   I have been looking at patch below primarily to learn how we could
> apply a similar technique to security.ima and security.evm for a
> namespaced IMA. From the paragraphs above I thought that you solved
> the problem of a shared filesystem where one now can write different
> security.capability xattrs by effectively supporting for example
> security.capability[uid=1000] and security.capability[uid=2000]

Interesting idea.  Worth considering.

> written into the filesystem. Each would then become visible as
> security.capability if the userns mapping is set appropriately.
> However, this doesn't seem to be how it is implemented. There seems

Indeed, when I was considering supporting multiple simulatenous
xattrs, I did it as something like:

struct vfs_ns_cap_data {
	struct {
		__le32 permitted;
		__le32 inheritable;
	} data[VFS_CAP_U32];
	__le32 rootid;
};

struct vfs_ns_cap {
	__le32 magic_etc;
	__le32 n_entries;
	struct ns_cap_data data[0];
}; // followed by n_entries of struct ns_cap_data

You're instead suggesting encoding the rootuid in the name,
which is interesting.

> to be only a single such entry with uid appended to it and, if it
> was a shared filesystem, the first one to set this attribute blocks
> everyone else from writing the xattr. Is that how it works? Would

Approximately - indeed there is only a single xattr.  But it can be
overwritten, so long as the writer has CAP_SETFCAP over the user_ns
which mounted the filesystem.

> that work differently with an overlay filesystem ? I think a similar
> model could also work for IMA, but maybe you have some thoughts. The
> only thing I would be concerned about is blocking the parent
> container's root user from setting an xattr.
> 
> Regards,
>    Stefan
> 
> 
> >
> >This patch introduces v3 of the security.capability xattr.  It builds a
> >vfs_ns_cap_data struct by appending a uid_t rootid to struct
> >vfs_cap_data.  This is the absolute uid_t (that is, the uid_t in user
> >namespace which mounted the filesystem, usually init_user_ns) of the
> >root id in whose namespaces the file capabilities may take effect.
> >
> >When a task asks to write a v2 security.capability xattr, if it is
> >privileged with respect to the userns which mounted the filesystem, then
> >nothing should change.  Otherwise, the kernel will transparently rewrite
> >the xattr as a v3 with the appropriate rootid.  This is done during the
> >execution of setxattr() to catch user-space-initiated capability writes.
> >Subsequently, any task executing the file which has the noted kuid as
> >its root uid, or which is in a descendent user_ns of such a user_ns,
> >will run the file with capabilities.
> >
> >Similarly when asking to read file capabilities, a v3 capability will
> >be presented as v2 if it applies to the caller's namespace.
> >
> >If a task writes a v3 security.capability, then it can provide a uid for
> >the xattr so long as the uid is valid in its own user namespace, and it
> >is privileged with CAP_SETFCAP over its namespace.  The kernel will
> >translate that rootid to an absolute uid, and write that to disk.  After
> >this, a task in the writer's namespace will not be able to use those
> >capabilities (unless rootid was 0), but a task in a namespace where the
> >given uid is root will.
> >
> >Only a single security.capability xattr may exist at a time for a given
> >file.  A task may overwrite an existing xattr so long as it is
> >privileged over the inode.  Note this is a departure from previous
> >semantics, which required privilege to remove a security.capability
> >xattr.  This check can be re-added if deemed useful.
> >
> >This allows a simple setxattr to work, allows tar/untar to work, and
> >allows us to tar in one namespace and untar in another while preserving
> >the capability, without risking leaking privilege into a parent
> >namespace.
> >
> >Example using tar:
> >
> >  $ cp /bin/sleep sleepx
> >  $ mkdir b1 b2
> >  $ lxc-usernsexec -m b:0:100000:1 -m b:1:$(id -u):1 -- chown 0:0 b1
> >  $ lxc-usernsexec -m b:0:100001:1 -m b:1:$(id -u):1 -- chown 0:0 b2
> >  $ lxc-usernsexec -m b:0:100000:1000 -- tar --xattrs-include=security.capability --xattrs -cf b1/sleepx.tar sleepx
> >  $ lxc-usernsexec -m b:0:100001:1000 -- tar --xattrs-include=security.capability --xattrs -C b2 -xf b1/sleepx.tar
> >  $ lxc-usernsexec -m b:0:100001:1000 -- getcap b2/sleepx
> >    b2/sleepx = cap_sys_admin+ep
> >  # /opt/ltp/testcases/bin/getv3xattr b2/sleepx
> >    v3 xattr, rootid is 100001
> >
> >A patch to linux-test-project adding a new set of tests for this
> >functionality is in the nsfscaps branch at github.com/hallyn/ltp
> >
> >Changelog:
> >    Nov 02 2016: fix invalid check at refuse_fcap_overwrite()
> >    Nov 07 2016: convert rootid from and to fs user_ns
> >    (From ebiederm: mar 28 2017)
> >      commoncap.c: fix typos - s/v4/v3
> >      get_vfs_caps_from_disk: clarify the fs_ns root access check
> >      nsfscaps: change the code split for cap_inode_setxattr()
> >    Apr 09 2017:
> >        don't return v3 cap for caps owned by current root.
> >       return a v2 cap for a true v2 cap in non-init ns
> >    Apr 18 2017:
> >       . Change the flow of fscap writing to support s_user_ns writing.
> >       . Remove refuse_fcap_overwrite().  The value of the previous
> >         xattr doesn't matter.
> >    Apr 24 2017:
> >       . incorporate Eric's incremental diff
> >       . move cap_convert_nscap to setxattr and simplify its usage
> >    May 8, 2017:
> >       . fix leaking dentry refcount in cap_inode_getsecurity
> >
> >Signed-off-by: Serge Hallyn <serge@...lyn.com>
> >---
> >  fs/xattr.c                      |   6 +
> >  include/linux/capability.h      |   2 +
> >  include/linux/security.h        |   2 +
> >  include/uapi/linux/capability.h |  22 +++-
> >  security/commoncap.c            | 270 +++++++++++++++++++++++++++++++++++++---
> >  5 files changed, 280 insertions(+), 22 deletions(-)
> >
> >diff --git a/fs/xattr.c b/fs/xattr.c
> >index 7e3317c..0a9dea4 100644
> >--- a/fs/xattr.c
> >+++ b/fs/xattr.c
> >@@ -444,6 +444,12 @@ setxattr(struct dentry *d, const char __user *name, const void __user *value,
> >  		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
> >  		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
> >  			posix_acl_fix_xattr_from_user(kvalue, size);
> >+		else if (strcmp(kname, XATTR_NAME_CAPS) == 0) {
> >+			error = cap_convert_nscap(d, &kvalue, size);
> >+			if (error < 0)
> >+				goto out;
> >+			size = error;
> >+		}
> >  	}
> >
> >  	error = vfs_setxattr(d, kname, kvalue, size, flags);
> >diff --git a/include/linux/capability.h b/include/linux/capability.h
> >index 6ffb67e..b52e278 100644
> >--- a/include/linux/capability.h
> >+++ b/include/linux/capability.h
> >@@ -248,4 +248,6 @@ extern bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns);
> >  /* audit system wants to get cap info from files as well */
> >  extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps);
> >
> >+extern int cap_convert_nscap(struct dentry *dentry, void **ivalue, size_t size);
> >+
> >  #endif /* !_LINUX_CAPABILITY_H */
> >diff --git a/include/linux/security.h b/include/linux/security.h
> >index 96899fa..bd49cc1 100644
> >--- a/include/linux/security.h
> >+++ b/include/linux/security.h
> >@@ -86,6 +86,8 @@ extern int cap_inode_setxattr(struct dentry *dentry, const char *name,
> >  extern int cap_inode_removexattr(struct dentry *dentry, const char *name);
> >  extern int cap_inode_need_killpriv(struct dentry *dentry);
> >  extern int cap_inode_killpriv(struct dentry *dentry);
> >+extern int cap_inode_getsecurity(struct inode *inode, const char *name,
> >+				 void **buffer, bool alloc);
> >  extern int cap_mmap_addr(unsigned long addr);
> >  extern int cap_mmap_file(struct file *file, unsigned long reqprot,
> >  			 unsigned long prot, unsigned long flags);
> >diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> >index 49bc062..fd4f87d 100644
> >--- a/include/uapi/linux/capability.h
> >+++ b/include/uapi/linux/capability.h
> >@@ -60,9 +60,13 @@ typedef struct __user_cap_data_struct {
> >  #define VFS_CAP_U32_2           2
> >  #define XATTR_CAPS_SZ_2         (sizeof(__le32)*(1 + 2*VFS_CAP_U32_2))
> >
> >-#define XATTR_CAPS_SZ           XATTR_CAPS_SZ_2
> >-#define VFS_CAP_U32             VFS_CAP_U32_2
> >-#define VFS_CAP_REVISION	VFS_CAP_REVISION_2
> >+#define VFS_CAP_REVISION_3	0x03000000
> >+#define VFS_CAP_U32_3           2
> >+#define XATTR_CAPS_SZ_3         (sizeof(__le32)*(2 + 2*VFS_CAP_U32_3))
> >+
> >+#define XATTR_CAPS_SZ           XATTR_CAPS_SZ_3
> >+#define VFS_CAP_U32             VFS_CAP_U32_3
> >+#define VFS_CAP_REVISION	VFS_CAP_REVISION_3
> >
> >  struct vfs_cap_data {
> >  	__le32 magic_etc;            /* Little endian */
> >@@ -72,6 +76,18 @@ struct vfs_cap_data {
> >  	} data[VFS_CAP_U32];
> >  };
> >
> >+/*
> >+ * same as vfs_cap_data but with a rootid at the end
> >+ */
> >+struct vfs_ns_cap_data {
> >+	__le32 magic_etc;
> >+	struct {
> >+		__le32 permitted;    /* Little endian */
> >+		__le32 inheritable;  /* Little endian */
> >+	} data[VFS_CAP_U32];
> >+	__le32 rootid;
> >+};
> >+
> >  #ifndef __KERNEL__
> >
> >  /*
> >diff --git a/security/commoncap.c b/security/commoncap.c
> >index 78b3783..c28d126 100644
> >--- a/security/commoncap.c
> >+++ b/security/commoncap.c
> >@@ -332,6 +332,209 @@ int cap_inode_killpriv(struct dentry *dentry)
> >  	return error;
> >  }
> >
> >+static bool rootid_owns_currentns(kuid_t kroot)
> >+{
> >+	struct user_namespace *ns;
> >+
> >+	if (!uid_valid(kroot))
> >+		return false;
> >+
> >+	for (ns = current_user_ns(); ; ns = ns->parent) {
> >+		if (from_kuid(ns, kroot) == 0)
> >+			return true;
> >+		if (ns == &init_user_ns)
> >+			break;
> >+	}
> >+
> >+	return false;
> >+}
> >+
> >+static __u32 sansflags(__u32 m)
> >+{
> >+	return m & ~VFS_CAP_FLAGS_EFFECTIVE;
> >+}
> >+
> >+static bool is_v2header(size_t size, __le32 magic)
> >+{
> >+	__u32 m = le32_to_cpu(magic);
> >+	if (size != XATTR_CAPS_SZ_2)
> >+		return false;
> >+	return sansflags(m) == VFS_CAP_REVISION_2;
> >+}
> >+
> >+static bool is_v3header(size_t size, __le32 magic)
> >+{
> >+	__u32 m = le32_to_cpu(magic);
> >+
> >+	if (size != XATTR_CAPS_SZ_3)
> >+		return false;
> >+	return sansflags(m) == VFS_CAP_REVISION_3;
> >+}
> >+
> >+/*
> >+ * getsecurity: We are called for security.* before any attempt to read the
> >+ * xattr from the inode itself.
> >+ *
> >+ * This gives us a chance to read the on-disk value and convert it.  If we
> >+ * return -EOPNOTSUPP, then vfs_getxattr() will call the i_op handler.
> >+ *
> >+ * Note we are not called by vfs_getxattr_alloc(), but that is only called
> >+ * by the integrity subsystem, which really wants the unconverted values -
> >+ * so that's good.
> >+ */
> >+int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
> >+			  bool alloc)
> >+{
> >+	int size, ret;
> >+	kuid_t kroot;
> >+	uid_t root, mappedroot;
> >+	char *tmpbuf = NULL;
> >+	struct vfs_cap_data *cap;
> >+	struct vfs_ns_cap_data *nscap;
> >+	struct dentry *dentry;
> >+	struct user_namespace *fs_ns;
> >+
> >+	if (strcmp(name, "capability") != 0)
> >+		return -EOPNOTSUPP;
> >+
> >+	dentry = d_find_alias(inode);
> >+	if (!dentry)
> >+		return -EINVAL;
> >+
> >+	size = sizeof(struct vfs_ns_cap_data);
> >+	ret = (int) vfs_getxattr_alloc(dentry, XATTR_NAME_CAPS,
> >+				 &tmpbuf, size, GFP_NOFS);
> >+	dput(dentry);
> >+
> >+	if (ret < 0)
> >+		return ret;
> >+
> >+	fs_ns = inode->i_sb->s_user_ns;
> >+	cap = (struct vfs_cap_data *) tmpbuf;
> >+	if (is_v2header((size_t) ret, cap->magic_etc)) {
> >+		/* If this is sizeof(vfs_cap_data) then we're ok with the
> >+		 * on-disk value, so return that.  */
> >+		if (alloc)
> >+			*buffer = tmpbuf;
> >+		else
> >+			kfree(tmpbuf);
> >+		return ret;
> >+	} else if (!is_v3header((size_t) ret, cap->magic_etc)) {
> >+		kfree(tmpbuf);
> >+		return -EINVAL;
> >+	}
> >+
> >+	nscap = (struct vfs_ns_cap_data *) tmpbuf;
> >+	root = le32_to_cpu(nscap->rootid);
> >+	kroot = make_kuid(fs_ns, root);
> >+
> >+	/* If the root kuid maps to a valid uid in current ns, then return
> >+	 * this as a nscap. */
> >+	mappedroot = from_kuid(current_user_ns(), kroot);
> >+	if (mappedroot != (uid_t)-1 && mappedroot != (uid_t)0) {
> >+		if (alloc) {
> >+			*buffer = tmpbuf;
> >+			nscap->rootid = cpu_to_le32(mappedroot);
> >+		} else
> >+			kfree(tmpbuf);
> >+		return size;
> >+	}
> >+
> >+	if (!rootid_owns_currentns(kroot)) {
> >+		kfree(tmpbuf);
> >+		return -EOPNOTSUPP;
> >+	}
> >+
> >+	/* This comes from a parent namespace.  Return as a v2 capability */
> >+	size = sizeof(struct vfs_cap_data);
> >+	if (alloc) {
> >+		*buffer = kmalloc(size, GFP_ATOMIC);
> >+		if (*buffer) {
> >+			struct vfs_cap_data *cap = *buffer;
> >+			__le32 nsmagic, magic;
> >+			magic = VFS_CAP_REVISION_2;
> >+			nsmagic = le32_to_cpu(nscap->magic_etc);
> >+			if (nsmagic & VFS_CAP_FLAGS_EFFECTIVE)
> >+				magic |= VFS_CAP_FLAGS_EFFECTIVE;
> >+			memcpy(&cap->data, &nscap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
> >+			cap->magic_etc = cpu_to_le32(magic);
> >+		}
> >+	}
> >+	kfree(tmpbuf);
> >+	return size;
> >+}
> >+
> >+static kuid_t rootid_from_xattr(const void *value, size_t size,
> >+				struct user_namespace *task_ns)
> >+{
> >+	const struct vfs_ns_cap_data *nscap = value;
> >+	uid_t rootid = 0;
> >+
> >+	if (size == XATTR_CAPS_SZ_3)
> >+		rootid = le32_to_cpu(nscap->rootid);
> >+
> >+	return make_kuid(task_ns, rootid);
> >+}
> >+
> >+static bool validheader(size_t size, __le32 magic)
> >+{
> >+	return is_v2header(size, magic) || is_v3header(size, magic);
> >+}
> >+
> >+/*
> >+ * User requested a write of security.capability.  If needed, update the
> >+ * xattr to change from v2 to v3, or to fixup the v3 rootid.
> >+ *
> >+ * If all is ok, we return the new size, on error return < 0.
> >+ */
> >+int cap_convert_nscap(struct dentry *dentry, void **ivalue, size_t size)
> >+{
> >+	struct vfs_ns_cap_data *nscap;
> >+	uid_t nsrootid;
> >+	const struct vfs_cap_data *cap = *ivalue;
> >+	__u32 magic, nsmagic;
> >+	struct inode *inode = d_backing_inode(dentry);
> >+	struct user_namespace *task_ns = current_user_ns(),
> >+		*fs_ns = inode->i_sb->s_user_ns;
> >+	kuid_t rootid;
> >+	size_t newsize;
> >+
> >+	if (!*ivalue)
> >+		return -EINVAL;
> >+	if (!validheader(size, cap->magic_etc))
> >+		return -EINVAL;
> >+	if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
> >+		return -EPERM;
> >+	if (size == XATTR_CAPS_SZ_2)
> >+		if (ns_capable(inode->i_sb->s_user_ns, CAP_SETFCAP))
> >+			/* user is privileged, just write the v2 */
> >+			return size;
> >+
> >+	rootid = rootid_from_xattr(*ivalue, size, task_ns);
> >+	if (!uid_valid(rootid))
> >+		return -EINVAL;
> >+
> >+	nsrootid = from_kuid(fs_ns, rootid);
> >+	if (nsrootid == -1)
> >+		return -EINVAL;
> >+
> >+	newsize = sizeof(struct vfs_ns_cap_data);
> >+	nscap = kmalloc(newsize, GFP_ATOMIC);
> >+	if (!nscap)
> >+		return -ENOMEM;
> >+	nscap->rootid = cpu_to_le32(nsrootid);
> >+	nsmagic = VFS_CAP_REVISION_3;
> >+	magic = le32_to_cpu(cap->magic_etc);
> >+	if (magic & VFS_CAP_FLAGS_EFFECTIVE)
> >+		nsmagic |= VFS_CAP_FLAGS_EFFECTIVE;
> >+	nscap->magic_etc = cpu_to_le32(nsmagic);
> >+	memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
> >+
> >+	kvfree(*ivalue);
> >+	*ivalue = nscap;
> >+	return newsize;
> >+}
> >+
> >  /*
> >   * Calculate the new process capability sets from the capability sets attached
> >   * to a file.
> >@@ -385,7 +588,10 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
> >  	__u32 magic_etc;
> >  	unsigned tocopy, i;
> >  	int size;
> >-	struct vfs_cap_data caps;
> >+	struct vfs_ns_cap_data data, *nscaps = &data;
> >+	struct vfs_cap_data *caps = (struct vfs_cap_data *) &data;
> >+	kuid_t rootkuid;
> >+	struct user_namespace *fs_ns = inode->i_sb->s_user_ns;
> >
> >  	memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
> >
> >@@ -393,18 +599,20 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
> >  		return -ENODATA;
> >
> >  	size = __vfs_getxattr((struct dentry *)dentry, inode,
> >-			      XATTR_NAME_CAPS, &caps, XATTR_CAPS_SZ);
> >+			      XATTR_NAME_CAPS, &data, XATTR_CAPS_SZ);
> >  	if (size == -ENODATA || size == -EOPNOTSUPP)
> >  		/* no data, that's ok */
> >  		return -ENODATA;
> >+
> >  	if (size < 0)
> >  		return size;
> >
> >  	if (size < sizeof(magic_etc))
> >  		return -EINVAL;
> >
> >-	cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc);
> >+	cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps->magic_etc);
> >
> >+	rootkuid = make_kuid(fs_ns, 0);
> >  	switch (magic_etc & VFS_CAP_REVISION_MASK) {
> >  	case VFS_CAP_REVISION_1:
> >  		if (size != XATTR_CAPS_SZ_1)
> >@@ -416,15 +624,27 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
> >  			return -EINVAL;
> >  		tocopy = VFS_CAP_U32_2;
> >  		break;
> >+	case VFS_CAP_REVISION_3:
> >+		if (size != XATTR_CAPS_SZ_3)
> >+			return -EINVAL;
> >+		tocopy = VFS_CAP_U32_3;
> >+		rootkuid = make_kuid(fs_ns, le32_to_cpu(nscaps->rootid));
> >+		break;
> >+
> >  	default:
> >  		return -EINVAL;
> >  	}
> >+	/* Limit the caps to the mounter of the filesystem
> >+	 * or the more limited uid specified in the xattr.
> >+	 */
> >+	if (!rootid_owns_currentns(rootkuid))
> >+		return -ENODATA;
> >
> >  	CAP_FOR_EACH_U32(i) {
> >  		if (i >= tocopy)
> >  			break;
> >-		cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted);
> >-		cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable);
> >+		cpu_caps->permitted.cap[i] = le32_to_cpu(caps->data[i].permitted);
> >+		cpu_caps->inheritable.cap[i] = le32_to_cpu(caps->data[i].inheritable);
> >  	}
> >
> >  	cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
> >@@ -462,8 +682,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
> >  	rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
> >  	if (rc < 0) {
> >  		if (rc == -EINVAL)
> >-			printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
> >-				__func__, rc, bprm->filename);
> >+			printk(KERN_NOTICE "Invalid argument reading file caps for %s\n",
> >+					bprm->filename);
> >  		else if (rc == -ENODATA)
> >  			rc = 0;
> >  		goto out;
> >@@ -660,15 +880,19 @@ int cap_bprm_secureexec(struct linux_binprm *bprm)
> >  int cap_inode_setxattr(struct dentry *dentry, const char *name,
> >  		       const void *value, size_t size, int flags)
> >  {
> >-	if (!strcmp(name, XATTR_NAME_CAPS)) {
> >-		if (!capable(CAP_SETFCAP))
> >-			return -EPERM;
> >+	/* Ignore non-security xattrs */
> >+	if (strncmp(name, XATTR_SECURITY_PREFIX,
> >+			sizeof(XATTR_SECURITY_PREFIX) - 1) != 0)
> >+		return 0;
> >+
> >+	/*
> >+	 * For XATTR_NAME_CAPS the check will be done in
> >+	 * cap_convert_nscap(), called by setxattr()
> >+	 */
> >+	if (strcmp(name, XATTR_NAME_CAPS) == 0)
> >  		return 0;
> >-	}
> >
> >-	if (!strncmp(name, XATTR_SECURITY_PREFIX,
> >-		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> >-	    !capable(CAP_SYS_ADMIN))
> >+	if (!capable(CAP_SYS_ADMIN))
> >  		return -EPERM;
> >  	return 0;
> >  }
> >@@ -686,15 +910,22 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name,
> >   */
> >  int cap_inode_removexattr(struct dentry *dentry, const char *name)
> >  {
> >-	if (!strcmp(name, XATTR_NAME_CAPS)) {
> >-		if (!capable(CAP_SETFCAP))
> >+	/* Ignore non-security xattrs */
> >+	if (strncmp(name, XATTR_SECURITY_PREFIX,
> >+			sizeof(XATTR_SECURITY_PREFIX) - 1) != 0)
> >+		return 0;
> >+
> >+	if (strcmp(name, XATTR_NAME_CAPS) == 0) {
> >+		/* security.capability gets namespaced */
> >+		struct inode *inode = d_backing_inode(dentry);
> >+		if (!inode)
> >+			return -EINVAL;
> >+		if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
> >  			return -EPERM;
> >  		return 0;
> >  	}
> >
> >-	if (!strncmp(name, XATTR_SECURITY_PREFIX,
> >-		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> >-	    !capable(CAP_SYS_ADMIN))
> >+	if (!capable(CAP_SYS_ADMIN))
> >  		return -EPERM;
> >  	return 0;
> >  }
> >@@ -1082,6 +1313,7 @@ struct security_hook_list capability_hooks[] = {
> >  	LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec),
> >  	LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
> >  	LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
> >+	LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),
> >  	LSM_HOOK_INIT(mmap_addr, cap_mmap_addr),
> >  	LSM_HOOK_INIT(mmap_file, cap_mmap_file),
> >  	LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid),
> 

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