On Wed, Mar 6, 2019 at 7:04 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > On 3/6/2019 7:54 AM, Ondrej Mosnacek wrote: > > On Fri, Feb 22, 2019 at 3:57 PM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote: > >> 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. > >> > >> Changes in v7: > >> - simplify the new security hook's interface > >> - rather than trying to extract kernfs data into common structures, just > >> pass the kernfs nodes themselves and add helper functions to > >> <linux/kernfs.h> for accessing their security xattrs > >> - in case other LSMs need more kernfs node attributes than the file mode > >> (uid/gid/...), they can simply add new helpers to <linux/kernfs.h> as > >> needed > >> - refactor "kernfs: use simple_xattrs for security attributes" to keep using > >> a single common simple_xattrs structure > >> - turns out having two separate simple_xattrs wouldn't work right (see > >> the definition of simple_xattr_list() in fs/xattr.c) > >> - drop unnecessary initializations from inode_doinit_use_xattr() > >> - move the IOP_XATTR check out of inode_doinit_use_xattr() > >> - add two kernfs cleanup patches > >> - these could be applied independently, but the rest of the patches depend on > >> them, so I'd rather they stay bundled with the rest to avoid cross-tree > >> conflicts > >> > >> v6: https://lore.kernel.org/selinux/20190214095015.16032-1-omosnace@xxxxxxxxxx/T/ > >> Changes in v6: > >> - remove copy-pasted duplicate macro definition > >> > >> v5: https://lore.kernel.org/selinux/20190205110638.30782-1-omosnace@xxxxxxxxxx/T/ > >> 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/ > >> > >> 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 1/7 simplifies the kernfs_iattrs structure and patch 2/7 optimizes > >> kernfs to not allocate kernfs_iattrs when getting the value of an xattr. > >> > >> Patch 3/7 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 4/7 would be a regression for > >> SELinux (due to the removal of ...notifysecctx() call. > >> > >> Patch 4/7 implements full security xattr support in kernfs using > >> simple_xattrs; patch 5/7 adds the new LSM hook; patch 6/7 implements the > >> new hook in SELinux; and patch 7/7 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 Rawhide (x86_64) when applied on top > >> of current Rawhide kernel (5.0.0-0.rc7.git2.1) [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://koji.fedoraproject.org/koji/taskinfo?taskID=32963825 > >> [4] https://github.com/SELinuxProject/selinux-testsuite/pull/48 > >> > >> Ondrej Mosnacek (7): > >> kernfs: clean up struct kernfs_iattrs > >> kernfs: do not alloc iattrs in kernfs_xattr_get > >> 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 | 28 ++-- > >> fs/kernfs/inode.c | 166 +++++++++------------ > >> fs/kernfs/kernfs-internal.h | 8 +- > >> fs/kernfs/symlink.c | 4 +- > >> include/linux/kernfs.h | 15 ++ > >> include/linux/lsm_hooks.h | 13 ++ > >> include/linux/security.h | 9 ++ > >> security/security.c | 6 + > >> security/selinux/hooks.c | 223 +++++++++++++++++++--------- > >> security/selinux/include/security.h | 1 + > >> 10 files changed, 290 insertions(+), 183 deletions(-) > >> > >> -- > >> 2.20.1 > > Ping about this series... Casey, are you OK with this new version? > > I'm still not wildly enthusiastic about it, but I can't > offer a better solution right now. You can add my > > Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> Thanks! -- Ondrej Mosnacek <omosnace at redhat dot com> Associate Software Engineer, Security Technologies Red Hat, Inc.
