Changes in v4: - reorder and rename hook arguments - avoid allocating kernfs_iattrs unless needed v3: https://lore.kernel.org/selinux/20190130114150.27807-1-omosnace@xxxxxxxxxx/T/ Changes in v3: - rename the hook to "kernfs_init_security" - change the hook interface to simply pass pointers to struct iattr and struct simple_xattrs of both the new node and its parent - add full security xattr support to kernfs (and fixup SELinux behavior to handle it properly) v2: https://lore.kernel.org/selinux/20190109162830.8309-1-omosnace@xxxxxxxxxx/T/ Changes in v2: - add docstring for the new hook in union security_list_options - initialize *ctx to NULL and *ctxlen to 0 in case the hook is not implemented v1: https://lore.kernel.org/selinux/20190109091028.24485-1-omosnace@xxxxxxxxxx/T/ TL;DR: This series adds a new security hook that allows to initialize the security context of kernfs properly, taking into account the parent context (and possibly other attributes). Kernfs nodes require special handling here, since they are not bound to specific inodes/superblocks, but instead represent the backing tree structure that is used to build the VFS tree when the kernfs tree is mounted. The kernfs nodes initially do not store any security context and rely on the LSM to assign some default context to inodes created over them. Kernfs inodes, however, allow setting an explicit context via the *setxattr(2) syscalls, in which case the context is stored inside the kernfs node's internal structure. SELinux (and possibly other LSMs) initialize the context of newly created FS objects based on the parent object's context (usually the child inherits the parent's context, unless the policy dictates otherwise). This is done by hooking the creation of the new inode corresponding to the newly created file/directory via security_inode_init_security() (most filesystems always create a fresh inode when a new FS object is created). However, kernfs nodes can be created "behind the scenes" while the filesystem is not mounted anywhere and thus no inodes can exist for them yet. Therefore, to allow maintaining similar behavior for kernfs nodes, a new LSM hook is needed, which will allow initializing the kernfs node's security context based on its own attributes and those of the parent's node. The main motivation for this change is that the userspace users of cgroupfs (which is built on kernfs) expect the usual security context inheritance to work under SELinux (see [1] and [2]). This functionality is required for better confinement of containers under SELinux. Patch 1/5 changes SELinux to fetch security context from extended attributes on kernfs filesystems, falling back to genfs-defined context if that fails. Without this patch the 2/5 would be a regression for SELinux (due to the removal of ...notifysecctx() call. Patch 2/5 implements full security xattr support in kernfs using simple_xattrs; patch 3/5 adds the new LSM hook; patch 4/5 implements the new hook in SELinux; and patch 5/5 modifies kernfs to call the new hook on new node creation. Testing: - passed the reproducer from the commit message of the last patch - passed SELinux testsuite on Fedora 29 (x86_64) when applied on top of current Rawhide kernel (5.0.0-0.rc5.git0.1) [3] - including the new proposed selinux-testsuite subtest [4] (adapted from the reproducer) [1] https://github.com/SELinuxProject/selinux-kernel/issues/39 [2] https://bugzilla.redhat.com/show_bug.cgi?id=1553803 [3] https://copr.fedorainfracloud.org/coprs/omos/kernel-testing/build/854148/ [4] https://github.com/SELinuxProject/selinux-testsuite/pull/48 Ondrej Mosnacek (5): selinux: try security xattr after genfs for kernfs filesystems kernfs: use simple_xattrs for security attributes LSM: add new hook for kernfs node initialization selinux: implement the kernfs_init_security hook kernfs: initialize security of newly created nodes fs/kernfs/dir.c | 64 +++++++- fs/kernfs/inode.c | 125 +++++++--------- fs/kernfs/kernfs-internal.h | 7 +- include/linux/lsm_hooks.h | 22 +++ include/linux/security.h | 14 ++ include/linux/xattr.h | 15 ++ security/security.c | 10 ++ security/selinux/hooks.c | 221 +++++++++++++++++++--------- security/selinux/include/security.h | 1 + 9 files changed, 328 insertions(+), 151 deletions(-) -- 2.20.1
