[PATCH v4 5/5] kernfs: initialize security of newly created nodes
Ondrej Mosnacek
omosnace at redhat.com
Tue Feb 5 08:59:15 UTC 2019
Use the new security_kernfs_init_security() hook to allow LSMs to
possibly assign a non-default security context to a newly created kernfs
node based on the attributes of the new node and also its parent node.
This fixes an issue with cgroupfs under SELinux, where newly created
cgroup subdirectories/files would not inherit its parent's context if
it had been set explicitly to a non-default value (other than the genfs
context specified by the policy). This can be reproduced as follows (on
Fedora/RHEL):
# mkdir /sys/fs/cgroup/unified/test
# # Need permissive to change the label under Fedora policy:
# setenforce 0
# chcon -t container_file_t /sys/fs/cgroup/unified/test
# ls -lZ /sys/fs/cgroup/unified
total 0
-r--r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 cgroup.controllers
-rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 cgroup.max.depth
-rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 cgroup.max.descendants
-rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 cgroup.procs
-r--r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 cgroup.stat
-rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 cgroup.subtree_control
-rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 cgroup.threads
drwxr-xr-x. 2 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 init.scope
drwxr-xr-x. 26 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:21 system.slice
drwxr-xr-x. 3 root root system_u:object_r:container_file_t:s0 0 Jan 29 03:15 test
drwxr-xr-x. 3 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:06 user.slice
# mkdir /sys/fs/cgroup/unified/test/subdir
Actual result:
# ls -ldZ /sys/fs/cgroup/unified/test/subdir
drwxr-xr-x. 2 root root system_u:object_r:cgroup_t:s0 0 Jan 29 03:15 /sys/fs/cgroup/unified/test/subdir
Expected result:
# ls -ldZ /sys/fs/cgroup/unified/test/subdir
drwxr-xr-x. 2 root root unconfined_u:object_r:container_file_t:s0 0 Jan 29 03:15 /sys/fs/cgroup/unified/test/subdir
Link: https://github.com/SELinuxProject/selinux-kernel/issues/39
Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>
---
fs/kernfs/dir.c | 57 +++++++++++++++++++++++++++++++++++--
fs/kernfs/inode.c | 25 +++++++++-------
fs/kernfs/kernfs-internal.h | 2 ++
include/linux/xattr.h | 15 ++++++++++
4 files changed, 86 insertions(+), 13 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index ad7e3356bcc5..735a6d382d9d 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -15,6 +15,7 @@
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/hash.h>
+#include <linux/stringhash.h>
#include "kernfs-internal.h"
@@ -616,7 +617,53 @@ struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
return NULL;
}
+static int kernfs_node_init_security(struct kernfs_node *parent,
+ struct kernfs_node *kn)
+{
+ struct simple_xattrs xattr_child, xattr_parent, *pxattr_parent;
+ struct iattr iattr_child, iattr_parent, *piattr_parent;
+ struct qstr q;
+ int ret;
+
+ if (!parent->iattr) {
+ kernfs_iattr_init(&iattr_parent, parent);
+ simple_xattrs_init(&xattr_parent);
+ piattr_parent = &iattr_parent;
+ pxattr_parent = &xattr_parent;
+ } else {
+ piattr_parent = &parent->iattr->ia_iattr;
+ pxattr_parent = &parent->iattr->xattrs_security;
+ }
+
+ kernfs_iattr_init(&iattr_child, kn);
+ simple_xattrs_init(&xattr_child);
+
+ q.name = kn->name;
+ q.hash_len = hashlen_string(parent, kn->name);
+
+ ret = security_kernfs_init_security(&q, piattr_parent, pxattr_parent,
+ &iattr_child, &xattr_child);
+ if (pxattr_parent == &xattr_parent)
+ simple_xattrs_free(&xattr_parent);
+ if (!ret && !simple_xattrs_empty(&xattr_child)) {
+ /*
+ * Child has new security xattrs, allocate its kernfs_iattrs
+ * and put our local xattrs in there.
+ */
+ struct kernfs_iattrs *attrs = kernfs_iattrs(kn);
+
+ if (!attrs) {
+ simple_xattrs_free(&xattr_child);
+ return -ENOMEM;
+ }
+ simple_xattrs_move(&attrs->xattrs_security, &xattr_child);
+ }
+ simple_xattrs_free(&xattr_child);
+ return ret;
+}
+
static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
+ struct kernfs_node *parent,
const char *name, umode_t mode,
kuid_t uid, kgid_t gid,
unsigned flags)
@@ -673,6 +720,12 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
goto err_out3;
}
+ if (parent) {
+ ret = kernfs_node_init_security(parent, kn);
+ if (ret)
+ goto err_out3;
+ }
+
return kn;
err_out3:
@@ -691,7 +744,7 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
{
struct kernfs_node *kn;
- kn = __kernfs_new_node(kernfs_root(parent),
+ kn = __kernfs_new_node(kernfs_root(parent), parent,
name, mode, uid, gid, flags);
if (kn) {
kernfs_get(parent);
@@ -961,7 +1014,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
INIT_LIST_HEAD(&root->supers);
root->next_generation = 1;
- kn = __kernfs_new_node(root, "", S_IFDIR | S_IRUGO | S_IXUGO,
+ kn = __kernfs_new_node(root, NULL, "", S_IFDIR | S_IRUGO | S_IXUGO,
GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
KERNFS_DIR);
if (!kn) {
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index f0e2cb4379c0..6a9084aecbe5 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -31,11 +31,22 @@ static const struct inode_operations kernfs_iops = {
.listxattr = kernfs_iop_listxattr,
};
-static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
+void kernfs_iattr_init(struct iattr *iattrs, struct kernfs_node *kn)
+{
+ /* assign default attributes */
+ iattrs->ia_mode = kn->mode;
+ iattrs->ia_uid = GLOBAL_ROOT_UID;
+ iattrs->ia_gid = GLOBAL_ROOT_GID;
+
+ ktime_get_real_ts64(&iattrs->ia_atime);
+ iattrs->ia_mtime = iattrs->ia_atime;
+ iattrs->ia_ctime = iattrs->ia_atime;
+}
+
+struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
{
static DEFINE_MUTEX(iattr_mutex);
struct kernfs_iattrs *ret;
- struct iattr *iattrs;
mutex_lock(&iattr_mutex);
@@ -45,16 +56,8 @@ static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
kn->iattr = kzalloc(sizeof(struct kernfs_iattrs), GFP_KERNEL);
if (!kn->iattr)
goto out_unlock;
- iattrs = &kn->iattr->ia_iattr;
-
- /* assign default attributes */
- iattrs->ia_mode = kn->mode;
- iattrs->ia_uid = GLOBAL_ROOT_UID;
- iattrs->ia_gid = GLOBAL_ROOT_GID;
- ktime_get_real_ts64(&iattrs->ia_atime);
- iattrs->ia_mtime = iattrs->ia_atime;
- iattrs->ia_ctime = iattrs->ia_atime;
+ kernfs_iattr_init(&kn->iattr->ia_iattr, kn);
simple_xattrs_init(&kn->iattr->xattrs_trusted);
simple_xattrs_init(&kn->iattr->xattrs_security);
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 93bf1dcd0306..ad80f438d8d4 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -90,6 +90,8 @@ int kernfs_iop_getattr(const struct path *path, struct kstat *stat,
u32 request_mask, unsigned int query_flags);
ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t size);
int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
+void kernfs_iattr_init(struct iattr *iattrs, struct kernfs_node *kn);
+struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn);
/*
* dir.c
diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index 6dad031be3c2..05fc6812d554 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -108,4 +108,19 @@ ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs, cha
void simple_xattr_list_add(struct simple_xattrs *xattrs,
struct simple_xattr *new_xattr);
+static inline int simple_xattrs_empty(struct simple_xattrs *xattrs)
+{
+ return list_empty(&xattrs->head);
+}
+
+/**
+ * Move the xattr list from @src to @dst, leaving @src empty.
+ */
+static inline void simple_xattrs_move(struct simple_xattrs *dst,
+ struct simple_xattrs *src)
+{
+ simple_xattrs_free(dst);
+ list_replace_init(&src->head, &dst->head);
+}
+
#endif /* _LINUX_XATTR_H */
--
2.20.1
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