linux-kernel - [PATCH 2/4] watch_queue: Add security hooks to rule on setting mount watches

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Message-ID: <159559630034.2141315.7836099179446814699.stgit@warthog.procyon.org.uk>
Date:   Fri, 24 Jul 2020 14:11:40 +0100
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     James Morris <jamorris@...ux.microsoft.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        linux-security-module@...r.kernel.org, dhowells@...hat.com,
        torvalds@...ux-foundation.org, casey@...aufler-ca.com,
        sds@...ho.nsa.gov, nicolas.dichtel@...nd.com, raven@...maw.net,
        christian@...uner.io, jlayton@...hat.com, kzak@...hat.com,
        mszeredi@...hat.com, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] watch_queue: Add security hooks to rule on setting mount
 watches

Add a security hook that will allow an LSM to rule on whether or not a
watch may be set on a mount.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: James Morris <jamorris@...ux.microsoft.com>
cc: Casey Schaufler <casey@...aufler-ca.com>
cc: Stephen Smalley <sds@...ho.nsa.gov>
cc: linux-security-module@...r.kernel.org
---

 include/linux/lsm_hook_defs.h |    3 +++
 include/linux/lsm_hooks.h     |    6 ++++++
 include/linux/security.h      |    8 ++++++++
 security/security.c           |    7 +++++++
 4 files changed, 24 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index af998f93d256..f6eaf8bd617b 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -264,6 +264,9 @@ LSM_HOOK(int, 0, post_notification, const struct cred *w_cred,
 #if defined(CONFIG_SECURITY) && defined(CONFIG_KEY_NOTIFICATIONS)
 LSM_HOOK(int, 0, watch_key, struct key *key)
 #endif /* CONFIG_SECURITY && CONFIG_KEY_NOTIFICATIONS */
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+LSM_HOOK(int, 0, watch_mount, struct watch *watch, struct path *path)
+#endif
 
 #ifdef CONFIG_SECURITY_NETWORK
 LSM_HOOK(int, 0, unix_stream_connect, struct sock *sock, struct sock *other,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 95b7c1d32062..56275145b91d 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1468,6 +1468,12 @@
  *	from a key or keyring.
  *	@key: The key to watch.
  *
+ * @watch_mount:
+ *	Check to see if a process is allowed to watch for mount topology change
+ *	notifications on a mount subtree.
+ *	@watch: The watch object
+ *	@path: The root of the subtree to watch.
+ *
  * Security hooks for using the eBPF maps and programs functionalities through
  * eBPF syscalls.
  *
diff --git a/include/linux/security.h b/include/linux/security.h
index 0a0a03b36a3b..318fdfe7f4d6 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1314,6 +1314,14 @@ static inline int security_watch_key(struct key *key)
 	return 0;
 }
 #endif
+#if defined(CONFIG_SECURITY) && defined(CONFIG_MOUNT_NOTIFICATIONS)
+int security_watch_mount(struct watch *watch, struct path *path);
+#else
+static inline int security_watch_mount(struct watch *watch, struct path *path)
+{
+	return 0;
+}
+#endif
 
 #ifdef CONFIG_SECURITY_NETWORK
 
diff --git a/security/security.c b/security/security.c
index 70a7ad357bc6..3cdf5039f727 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2067,6 +2067,13 @@ int security_watch_key(struct key *key)
 }
 #endif
 
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+int security_watch_mount(struct watch *watch, struct path *path)
+{
+	return call_int_hook(watch_mount, 0, watch, path);
+}
+#endif
+
 #ifdef CONFIG_SECURITY_NETWORK
 
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)