On Fri, Feb 22, 2019 at 9:57 AM 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(-) I just merged this patchset into selinux/next, thanks everyone. Ondrej, every patch in the patchset except for one required some amount of merge fixups, please take a look and make sure everything in the selinux/next branch still looks right to you. -- paul moore www.paul-moore.com
