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Message-ID: <20260209.yeeh3ieDuz9u@digikod.net>
Date: Mon, 9 Feb 2026 18:51:21 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Günther Noack <gnoack3000@...il.com>
Cc: John Johansen <john.johansen@...onical.com>,
Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
"Serge E . Hallyn" <serge@...lyn.com>, Tingmao Wang <m@...wtm.org>,
Justin Suess <utilityemal77@...il.com>, linux-security-module@...r.kernel.org,
Samasth Norway Ananda <samasth.norway.ananda@...cle.com>, Matthieu Buffet <matthieu@...fet.re>,
Mikhail Ivanov <ivanov.mikhail1@...wei-partners.com>, konstantin.meskhidze@...wei.com,
Demi Marie Obenour <demiobenour@...il.com>, Alyssa Ross <hi@...ssa.is>, Jann Horn <jannh@...gle.com>,
Tahera Fahimi <fahimitahera@...il.com>, Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v4 1/6] lsm: Add LSM hook security_unix_find
On Mon, Feb 09, 2026 at 12:10:11AM +0100, Günther Noack wrote:
> From: Justin Suess <utilityemal77@...il.com>
>
> Add a LSM hook security_unix_find.
>
> This hook is called to check the path of a named unix socket before a
> connection is initiated. The peer socket may be inspected as well.
>
> Why existing hooks are unsuitable:
>
> Existing socket hooks, security_unix_stream_connect(),
> security_unix_may_send(), and security_socket_connect() don't provide
> TOCTOU-free / namespace independent access to the paths of sockets.
>
> (1) We cannot resolve the path from the struct sockaddr in existing hooks.
> This requires another path lookup. A change in the path between the
> two lookups will cause a TOCTOU bug.
>
> (2) We cannot use the struct path from the listening socket, because it
> may be bound to a path in a different namespace than the caller,
> resulting in a path that cannot be referenced at policy creation time.
>
> Cc: Günther Noack <gnoack3000@...il.com>
> Cc: Tingmao Wang <m@...wtm.org>
> Signed-off-by: Justin Suess <utilityemal77@...il.com>
> ---
> include/linux/lsm_hook_defs.h | 5 +++++
> include/linux/security.h | 11 +++++++++++
> net/unix/af_unix.c | 9 +++++++++
> security/security.c | 20 ++++++++++++++++++++
> 4 files changed, 45 insertions(+)
>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 8c42b4bde09c..7a0fd3dbfa29 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -317,6 +317,11 @@ LSM_HOOK(int, 0, post_notification, const struct cred *w_cred,
> LSM_HOOK(int, 0, watch_key, struct key *key)
> #endif /* CONFIG_SECURITY && CONFIG_KEY_NOTIFICATIONS */
>
> +#if defined(CONFIG_SECURITY_NETWORK) && defined(CONFIG_SECURITY_PATH)
> +LSM_HOOK(int, 0, unix_find, const struct path *path, struct sock *other,
> + int flags)
> +#endif /* CONFIG_SECURITY_NETWORK && CONFIG_SECURITY_PATH */
> +
> #ifdef CONFIG_SECURITY_NETWORK
> LSM_HOOK(int, 0, unix_stream_connect, struct sock *sock, struct sock *other,
> struct sock *newsk)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 83a646d72f6f..99a33d8eb28d 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -1931,6 +1931,17 @@ static inline int security_mptcp_add_subflow(struct sock *sk, struct sock *ssk)
> }
> #endif /* CONFIG_SECURITY_NETWORK */
>
> +#if defined(CONFIG_SECURITY_NETWORK) && defined(CONFIG_SECURITY_PATH)
> +
> +int security_unix_find(const struct path *path, struct sock *other, int flags);
> +
> +#else /* CONFIG_SECURITY_NETWORK && CONFIG_SECURITY_PATH */
> +static inline int security_unix_find(const struct path *path, struct sock *other, int flags)
> +{
> + return 0;
> +}
> +#endif /* CONFIG_SECURITY_NETWORK && CONFIG_SECURITY_PATH */
> +
> #ifdef CONFIG_SECURITY_INFINIBAND
> int security_ib_pkey_access(void *sec, u64 subnet_prefix, u16 pkey);
> int security_ib_endport_manage_subnet(void *sec, const char *name, u8 port_num);
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index d0511225799b..db9d279b3883 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1226,10 +1226,19 @@ static struct sock *unix_find_bsd(struct sockaddr_un *sunaddr, int addr_len,
> if (!S_ISSOCK(inode->i_mode))
> goto path_put;
>
> + err = -ECONNREFUSED;
We don't see it in this patch but err is already set to -ECONNREFUSED.
This line might be confusing, and unrelated to the goal of this patch,
so we should remove it.
> sk = unix_find_socket_byinode(inode);
> if (!sk)
> goto path_put;
>
> + /*
> + * We call the hook because we know that the inode is a socket
> + * and we hold a valid reference to it via the path.
This comment can be alligned with 80 columns.
> + */
> + err = security_unix_find(&path, sk, flags);
This hook makes sense and is quite generic.
> + if (err)
> + goto sock_put;
> +
> err = -EPROTOTYPE;
> if (sk->sk_type == type)
> touch_atime(&path);
> diff --git a/security/security.c b/security/security.c
> index 31a688650601..9e9515955098 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -4731,6 +4731,26 @@ int security_mptcp_add_subflow(struct sock *sk, struct sock *ssk)
>
> #endif /* CONFIG_SECURITY_NETWORK */
>
> +#if defined(CONFIG_SECURITY_NETWORK) && defined(CONFIG_SECURITY_PATH)
> +/*
This should be a docstring like other hooks: /**
> + * security_unix_find() - Check if a named AF_UNIX socket can connect
> + * @path: path of the socket being connected to
> + * @other: peer sock
> + * @flags: flags associated with the socket
> + *
> + * This hook is called to check permissions before connecting to a named
> + * AF_UNIX socket.
> + *
> + * Return: Returns 0 if permission is granted.
> + */
> +int security_unix_find(const struct path *path, struct sock *other, int flags)
> +{
> + return call_int_hook(unix_find, path, other, flags);
> +}
> +EXPORT_SYMBOL(security_unix_find);
> +
> +#endif /* CONFIG_SECURITY_NETWORK && CONFIG_SECURITY_PATH */
> +
> #ifdef CONFIG_SECURITY_INFINIBAND
> /**
> * security_ib_pkey_access() - Check if access to an IB pkey is allowed
> --
> 2.52.0
>
>
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