linux-kernel - Re: [PATCH v7 1/4] Landlock: Add abstract unix socket connect restriction

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Message-ID: <20240726.Nohde4vooy3A@digikod.net>
Date: Fri, 26 Jul 2024 10:07:38 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: Tahera Fahimi <fahimitahera@...il.com>
Cc: gnoack@...gle.com, paul@...l-moore.com, jmorris@...ei.org, 
	serge@...lyn.com, linux-security-module@...r.kernel.org, 
	linux-kernel@...r.kernel.org, bjorn3_gh@...tonmail.com, jannh@...gle.com, 
	outreachy@...ts.linux.dev, netdev@...r.kernel.org
Subject: Re: [PATCH v7 1/4] Landlock: Add abstract unix socket connect
 restriction

On Wed, Jul 17, 2024 at 10:15:19PM -0600, Tahera Fahimi wrote:
> The patch introduces a new "scoped" attribute to the
> landlock_ruleset_attr that can specify "LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET"
> to scope abstract unix sockets from connecting to a process outside of
> the same landlock domain.
> 
> This patch implement two hooks, "unix_stream_connect" and "unix_may_send" to
> enforce this restriction.
> 
> Signed-off-by: Tahera Fahimi <fahimitahera@...il.com>
> 
> -------
> v7:
>  - Using socket's file credentials for both connected(STREAM) and
>    non-connected(DGRAM) sockets.
>  - Adding "domain_sock_scope" instead of the domain scoping mechanism used in
>    ptrace ensures that if a server's domain is accessible from the client's
>    domain (where the client is more privileged than the server), the client
>    can connect to the server in all edge cases.
>  - Removing debug codes.
> v6:
>  - Removing curr_ruleset from landlock_hierarchy, and switching back to use
>    the same domain scoping as ptrace.
>  - code clean up.
> v5:
>  - Renaming "LANDLOCK_*_ACCESS_SCOPE" to "LANDLOCK_*_SCOPE"
>  - Adding curr_ruleset to hierarachy_ruleset structure to have access from
>    landlock_hierarchy to its respective landlock_ruleset.
>  - Using curr_ruleset to check if a domain is scoped while walking in the
>    hierarchy of domains.
>  - Modifying inline comments.
> V4:
>  - Rebased on Günther's Patch:
>    https://lore.kernel.org/all/20240610082115.1693267-1-gnoack@google.com/
>    so there is no need for "LANDLOCK_SHIFT_ACCESS_SCOPE", then it is removed.
>  - Adding get_scope_accesses function to check all scoped access masks in a ruleset.
>  - Using file's FD credentials instead of credentials stored in peer_cred
>    for datagram sockets. (see discussion in [1])
>  - Modifying inline comments.
> V3:
>  - Improving commit description.
>  - Introducing "scoped" attribute to landlock_ruleset_attr for IPC scoping
>    purpose, and adding related functions.
>  - Changing structure of ruleset based on "scoped".
>  - Removing rcu lock and using unix_sk lock instead.
>  - Introducing scoping for datagram sockets in unix_may_send.
> V2:
>  - Removing wrapper functions
> 
> [1]https://lore.kernel.org/outreachy/Zmi8Ydz4Z6tYtpY1@tahera-OptiPlex-5000/T/#m8cdf33180d86c7ec22932e2eb4ef7dd4fc94c792
> -------
> 
> Signed-off-by: Tahera Fahimi <fahimitahera@...il.com>
> ---
>  include/uapi/linux/landlock.h |  29 +++++++++
>  security/landlock/limits.h    |   3 +
>  security/landlock/ruleset.c   |   7 ++-
>  security/landlock/ruleset.h   |  23 ++++++-
>  security/landlock/syscalls.c  |  14 +++--
>  security/landlock/task.c      | 112 ++++++++++++++++++++++++++++++++++
>  6 files changed, 181 insertions(+), 7 deletions(-)
> 
> diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
> index 68625e728f43..9cd881673434 100644
> --- a/include/uapi/linux/landlock.h
> +++ b/include/uapi/linux/landlock.h
> @@ -37,6 +37,12 @@ struct landlock_ruleset_attr {
>  	 * rule explicitly allow them.
>  	 */
>  	__u64 handled_access_net;
> +	/**
> +	 * @scoped: Bitmask of scopes (cf. `Scope flags`_)
> +	 * restricting a Landlock domain from accessing outside
> +	 * resources(e.g. IPCs).
> +	 */
> +	__u64 scoped;
>  };
>  
>  /*
> @@ -266,4 +272,27 @@ struct landlock_net_port_attr {
>  #define LANDLOCK_ACCESS_NET_BIND_TCP			(1ULL << 0)
>  #define LANDLOCK_ACCESS_NET_CONNECT_TCP			(1ULL << 1)
>  /* clang-format on */
> +
> +/**
> + * DOC: scope
> + *
> + * .scoped attribute handles a set of restrictions on kernel IPCs through
> + * the following flags.

If you look at the generated documentation (once this doc is properly
included), you'll see that this line ends in the Network flags section.

> + *
> + * Scope flags
> + * ~~~~~~~~~~~
> + *
> + * These flags enable to restrict a sandboxed process from a set of IPC
> + * actions. Setting a flag for a ruleset will isolate the Landlock domain
> + * to forbid connections to resources outside the domain.
> + *
> + * IPCs with scoped actions:

There is a formating issue here.

> + * - %LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET: Restrict a sandboxed process
> + *   from connecting to an abstract unix socket created by a process
> + *   outside the related Landlock domain (e.g. a parent domain or a
> + *   non-sandboxed process).
> + */
> +/* clang-format off */
> +#define LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET		(1ULL << 0)
> +/* clang-format on*/
>  #endif /* _UAPI_LINUX_LANDLOCK_H */