Re: [PATCH v5 2/9] landlock: Control pathname UNIX domain socket resolution by path

["Mickaël Salaün" <mic@digikod.net>]

On Wed, Feb 18, 2026 at 10:37:16AM +0100, Mickaël Salaün wrote:
> On Sun, Feb 15, 2026 at 11:51:50AM +0100, Günther Noack wrote:
> > * Add a new access right LANDLOCK_ACCESS_FS_RESOLVE_UNIX, which
> >   controls the look up operations for named UNIX domain sockets.  The
> >   resolution happens during connect() and sendmsg() (depending on
> >   socket type).
> > * Hook into the path lookup in unix_find_bsd() in af_unix.c, using a
> >   LSM hook.  Make policy decisions based on the new access rights
> > * Increment the Landlock ABI version.
> > * Minor test adaptions to keep the tests working.
> > 
> > With this access right, access is granted if either of the following
> > conditions is met:
> > 
> > * The target socket's filesystem path was allow-listed using a
> >   LANDLOCK_RULE_PATH_BENEATH rule, *or*:
> > * The target socket was created in the same Landlock domain in which
> >   LANDLOCK_ACCESS_FS_RESOLVE_UNIX was restricted.
> > 
> > In case of a denial, connect() and sendmsg() return EACCES, which is
> > the same error as it is returned if the user does not have the write
> > bit in the traditional Unix file system permissions of that file.
> > 
> > This feature was created with substantial discussion and input from
> > Justin Suess, Tingmao Wang and Mickaël Salaün.
> > 
> > Cc: Tingmao Wang <m@maowtm.org>
> > Cc: Justin Suess <utilityemal77@gmail.com>
> > Cc: Mickaël Salaün <mic@digikod.net>
> > Suggested-by: Jann Horn <jannh@google.com>
> > Link: https://github.com/landlock-lsm/linux/issues/36
> > Signed-off-by: Günther Noack <gnoack3000@gmail.com>
> > ---
> >  include/uapi/linux/landlock.h                |  10 ++
> >  security/landlock/access.h                   |  11 +-
> >  security/landlock/audit.c                    |   1 +
> >  security/landlock/fs.c                       | 102 ++++++++++++++++++-
> >  security/landlock/limits.h                   |   2 +-
> >  security/landlock/syscalls.c                 |   2 +-
> >  tools/testing/selftests/landlock/base_test.c |   2 +-
> >  tools/testing/selftests/landlock/fs_test.c   |   5 +-
> >  8 files changed, 128 insertions(+), 7 deletions(-)

> > index 60ff217ab95b..8d0edf94037d 100644
> > --- a/security/landlock/audit.c
> > +++ b/security/landlock/audit.c
> > @@ -37,6 +37,7 @@ static const char *const fs_access_strings[] = {
> >  	[BIT_INDEX(LANDLOCK_ACCESS_FS_REFER)] = "fs.refer",
> >  	[BIT_INDEX(LANDLOCK_ACCESS_FS_TRUNCATE)] = "fs.truncate",
> >  	[BIT_INDEX(LANDLOCK_ACCESS_FS_IOCTL_DEV)] = "fs.ioctl_dev",
> > +	[BIT_INDEX(LANDLOCK_ACCESS_FS_RESOLVE_UNIX)] = "fs.resolve_unix",
> >  };
> >  
> >  static_assert(ARRAY_SIZE(fs_access_strings) == LANDLOCK_NUM_ACCESS_FS);
> > diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> > index e764470f588c..76035c6f2bf1 100644
> > --- a/security/landlock/fs.c
> > +++ b/security/landlock/fs.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/lsm_hooks.h>
> >  #include <linux/mount.h>
> >  #include <linux/namei.h>
> > +#include <linux/net.h>
> >  #include <linux/path.h>
> >  #include <linux/pid.h>
> >  #include <linux/rcupdate.h>
> > @@ -314,7 +315,8 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
> >  	LANDLOCK_ACCESS_FS_WRITE_FILE | \
> >  	LANDLOCK_ACCESS_FS_READ_FILE | \
> >  	LANDLOCK_ACCESS_FS_TRUNCATE | \
> > -	LANDLOCK_ACCESS_FS_IOCTL_DEV)
> > +	LANDLOCK_ACCESS_FS_IOCTL_DEV | \
> > +	LANDLOCK_ACCESS_FS_RESOLVE_UNIX)
> >  /* clang-format on */
> >  
> >  /*
> > @@ -1561,6 +1563,103 @@ static int hook_path_truncate(const struct path *const path)
> >  	return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE);
> >  }
> >  
> > +/**
> > + * unmask_scoped_access - Remove access right bits in @masks in all layers
> > + *                        where @client and @server have the same domain
> > + *
> > + * This does the same as domain_is_scoped(), but unmasks bits in @masks.
> > + * It can not return early as domain_is_scoped() does.

Why can't we use the same logic as for other scopes?

> > + *
> > + * @client: Client domain
> > + * @server: Server domain
> > + * @masks: Layer access masks to unmask
> > + * @access: Access bit that controls scoping
> > + */
> > +static void unmask_scoped_access(const struct landlock_ruleset *const client,
> > +				 const struct landlock_ruleset *const server,
> > +				 struct layer_access_masks *const masks,
> > +				 const access_mask_t access)
> 
> This helper should be moved to task.c and factored out with
> domain_is_scoped().  This should be a dedicated patch.

Well, if domain_is_scoped() can be refactored and made generic, it would
make more sense to move it to domain.c

> 
> > +{
> > +	int client_layer, server_layer;
> > +	const struct landlock_hierarchy *client_walker, *server_walker;
> > +
> > +	if (WARN_ON_ONCE(!client))
> > +		return; /* should not happen */
> > +
> > +	if (!server)
> > +		return; /* server has no Landlock domain; nothing to clear */
> > +
> > +	client_layer = client->num_layers - 1;
> > +	client_walker = client->hierarchy;
> > +	server_layer = server->num_layers - 1;
> > +	server_walker = server->hierarchy;
> > +
> > +	/*
> > +	 * Clears the access bits at all layers where the client domain is the
> > +	 * same as the server domain.  We start the walk at min(client_layer,
> > +	 * server_layer).  The layer bits until there can not be cleared because
> > +	 * either the client or the server domain is missing.
> > +	 */
> > +	for (; client_layer > server_layer; client_layer--)
> > +		client_walker = client_walker->parent;
> > +
> > +	for (; server_layer > client_layer; server_layer--)
> > +		server_walker = server_walker->parent;
> > +
> > +	for (; client_layer >= 0; client_layer--) {
> > +		if (masks->access[client_layer] & access &&
> > +		    client_walker == server_walker)
> > +			masks->access[client_layer] &= ~access;
> > +
> > +		client_walker = client_walker->parent;
> > +		server_walker = server_walker->parent;
> > +	}
> > +}