On Tue, Feb 5, 2019 at 12:06 PM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote: > Changes in v5: > - fix misplaced semicolon detected by 0day robot > > v4: https://lore.kernel.org/selinux/20190205085915.5183-1-omosnace@xxxxxxxxxx/T/ > 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 Are there any further comments/objections to this patchset (other than the duplicate include in patch #1)? I'd like to accumulate changes (if any are needed) before posting v6. Thanks, -- Ondrej Mosnacek <omosnace at redhat dot com> Associate Software Engineer, Security Technologies Red Hat, Inc.
