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@xxxxxxxxxx>
---
fs/kernfs/dir.c | 35 +++++++++++++++++++++++++++++++++--
fs/kernfs/inode.c | 2 +-
fs/kernfs/kernfs-internal.h | 1 +
3 files changed, 35 insertions(+), 3 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index ad7e3356bcc5..797199a748d7 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 +617,31 @@ 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 kernfs_iattrs *attrs, *pattrs;
+ struct qstr q;
+
+ attrs = kernfs_iattrs(kn);
+ if (!attrs)
+ return -ENOMEM;
+
+ pattrs = kernfs_iattrs(parent);
+ if (!pattrs)
+ return -ENOMEM;
+
+ q.name = kn->name;
+ q.hash_len = hashlen_string(parent, kn->name);
+
+ return security_kernfs_init_security(&q, &attrs->ia_iattr,
+ &attrs->xattrs_security,
+ &pattrs->ia_iattr,
+ &pattrs->xattrs_security);
+}
+
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 +698,12 @@ 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 +722,7 @@ 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 +992,7 @@ 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..645c404b8644 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -31,7 +31,7 @@ static const struct inode_operations kernfs_iops = {
.listxattr = kernfs_iop_listxattr,
};
-static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
+struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
{
static DEFINE_MUTEX(iattr_mutex);
struct kernfs_iattrs *ret;
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 93bf1dcd0306..90215f8e503a 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -90,6 +90,7 @@ 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);
+struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn);
/*
* dir.c
--
2.20.1
