On Tue, Mar 16, 2021 at 09:42:47PM +0100, Mickaël Salaün wrote: > From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > > Using Landlock objects and ruleset, it is possible to tag inodes > according to a process's domain. To enable an unprivileged process to > express a file hierarchy, it first needs to open a directory (or a file) > and pass this file descriptor to the kernel through > landlock_add_rule(2). When checking if a file access request is > allowed, we walk from the requested dentry to the real root, following > the different mount layers. The access to each "tagged" inodes are > collected according to their rule layer level, and ANDed to create > access to the requested file hierarchy. This makes possible to identify > a lot of files without tagging every inodes nor modifying the > filesystem, while still following the view and understanding the user > has from the filesystem. > > Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not > keep the same struct inodes for the same inodes whereas these inodes are > in use. > > This commit adds a minimal set of supported filesystem access-control > which doesn't enable to restrict all file-related actions. This is the > result of multiple discussions to minimize the code of Landlock to ease > review. Thanks to the Landlock design, extending this access-control > without breaking user space will not be a problem. Moreover, seccomp > filters can be used to restrict the use of syscall families which may > not be currently handled by Landlock. > > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Anton Ivanov <anton.ivanov@xxxxxxxxxxxxxxxxxx> > Cc: James Morris <jmorris@xxxxxxxxx> > Cc: Jann Horn <jannh@xxxxxxxxxx> > Cc: Jeff Dike <jdike@xxxxxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: Richard Weinberger <richard@xxxxxx> > Cc: Serge E. Hallyn <serge@xxxxxxxxxx> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/20210316204252.427806-8-mic@xxxxxxxxxxx > [...] > + spin_lock(&sb->s_inode_list_lock); > + list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { > + struct landlock_object *object; > + > + /* Only handles referenced inodes. */ > + if (!atomic_read(&inode->i_count)) > + continue; > + > + /* > + * Checks I_FREEING and I_WILL_FREE to protect against a race > + * condition when release_inode() just called iput(), which > + * could lead to a NULL dereference of inode->security or a > + * second call to iput() for the same Landlock object. Also > + * checks I_NEW because such inode cannot be tied to an object. > + */ > + spin_lock(&inode->i_lock); > + if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) { > + spin_unlock(&inode->i_lock); > + continue; > + } This (and elsewhere here) seems like a lot of inode internals getting exposed. Can any of this be repurposed into helpers? I see this test scattered around the kernel a fair bit: $ git grep I_FREEING | grep I_WILL_FREE | grep I_NEW | wc -l 9 > +static inline u32 get_mode_access(const umode_t mode) > +{ > + switch (mode & S_IFMT) { > + case S_IFLNK: > + return LANDLOCK_ACCESS_FS_MAKE_SYM; > + case 0: > + /* A zero mode translates to S_IFREG. */ > + case S_IFREG: > + return LANDLOCK_ACCESS_FS_MAKE_REG; > + case S_IFDIR: > + return LANDLOCK_ACCESS_FS_MAKE_DIR; > + case S_IFCHR: > + return LANDLOCK_ACCESS_FS_MAKE_CHAR; > + case S_IFBLK: > + return LANDLOCK_ACCESS_FS_MAKE_BLOCK; > + case S_IFIFO: > + return LANDLOCK_ACCESS_FS_MAKE_FIFO; > + case S_IFSOCK: > + return LANDLOCK_ACCESS_FS_MAKE_SOCK; > + default: > + WARN_ON_ONCE(1); > + return 0; > + } I'm assuming this won't be reachable from userspace. > [...] > index a5d6ef334991..f8e8e980454c 100644 > --- a/security/landlock/setup.c > +++ b/security/landlock/setup.c > @@ -11,17 +11,24 @@ > > #include "common.h" > #include "cred.h" > +#include "fs.h" > #include "ptrace.h" > #include "setup.h" > > +bool landlock_initialized __lsm_ro_after_init = false; > + > struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = { > .lbs_cred = sizeof(struct landlock_cred_security), > + .lbs_inode = sizeof(struct landlock_inode_security), > + .lbs_superblock = sizeof(struct landlock_superblock_security), > }; > > static int __init landlock_init(void) > { > landlock_add_cred_hooks(); > landlock_add_ptrace_hooks(); > + landlock_add_fs_hooks(); > + landlock_initialized = true; I think this landlock_initialized is logically separate from the optional DEFINE_LSM "enabled" variable, but I thought I'd double check. :) It seems like it's used here to avoid releasing superblocks before landlock_init() is called? What is the scenario where that happens? > pr_info("Up and running.\n"); > return 0; > } > diff --git a/security/landlock/setup.h b/security/landlock/setup.h > index 9fdbf33fcc33..1daffab1ab4b 100644 > --- a/security/landlock/setup.h > +++ b/security/landlock/setup.h > @@ -11,6 +11,8 @@ > > #include <linux/lsm_hooks.h> > > +extern bool landlock_initialized; > + > extern struct lsm_blob_sizes landlock_blob_sizes; > > #endif /* _SECURITY_LANDLOCK_SETUP_H */ > -- > 2.30.2 > The locking and inode semantics are pretty complex, but since, again, it's got significant test and syzkaller coverage, it looks good to me. With the inode helper cleanup: Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
