[PATCH 1/1] lsm: adds process attribute getter for Landlock

[enlightened@chromium.org]

From: Shervin Oloumi <enlightened@chromium.org>

Adds a new getprocattr hook function to the Landlock LSM, which tracks
the landlocked state of the process. This is invoked when user-space
reads /proc/[pid]/attr/current to determine whether a given process is
sand-boxed using Landlock.

Adds a new directory for landlock under the process attribute
filesystem, and defines "current" as a read-only process attribute entry
for landlock.

Signed-off-by: Shervin Oloumi <enlightened@chromium.org>
---
 fs/proc/base.c         | 11 +++++++++++
 security/landlock/fs.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9e479d7d202b..3ab29a965911 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2851,6 +2851,13 @@ static const struct pid_entry apparmor_attr_dir_stuff[] = {
 LSM_DIR_OPS(apparmor);
 #endif
 
+#ifdef CONFIG_SECURITY_LANDLOCK
+static const struct pid_entry landlock_attr_dir_stuff[] = {
+       ATTR("landlock", "current", 0444),
+};
+LSM_DIR_OPS(landlock);
+#endif
+
 static const struct pid_entry attr_dir_stuff[] = {
 	ATTR(NULL, "current",		0666),
 	ATTR(NULL, "prev",		0444),
@@ -2866,6 +2873,10 @@ static const struct pid_entry attr_dir_stuff[] = {
 	DIR("apparmor",			0555,
 	    proc_apparmor_attr_dir_inode_ops, proc_apparmor_attr_dir_ops),
 #endif
+#ifdef CONFIG_SECURITY_LANDLOCK
+       DIR("landlock",                  0555,
+	    proc_landlock_attr_dir_inode_ops, proc_landlock_attr_dir_ops),
+#endif
 };
 
 static int proc_attr_dir_readdir(struct file *file, struct dir_context *ctx)
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index adcea0fe7e68..179ba22ce0fc 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -1280,6 +1280,37 @@ static int hook_file_truncate(struct file *const file)
 	return -EACCES;
 }
 
+/* process attribute interfaces */
+
+/**
+ * landlock_getprocattr - Landlock process attribute getter
+ * @p: the object task
+ * @name: the name of the attribute in /proc/.../attr
+ * @value: where to put the result
+ *
+ * Writes the status of landlock to value
+ *
+ * Returns the length of the result inside value
+ */
+static int landlock_getprocattr(struct task_struct *task, const char *name,
+				char **value)
+{
+	char *val;
+	int slen;
+
+	if (strcmp(name, "current") != 0)
+		return -EINVAL;
+
+	if (landlocked(task))
+		val = "landlocked:1";
+	else
+		val = "landlocked:0";
+
+	slen = strlen(val);
+	*value = val;
+	return slen;
+}
+
 static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(inode_free_security, hook_inode_free_security),
 
@@ -1302,6 +1333,8 @@ static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(file_alloc_security, hook_file_alloc_security),
 	LSM_HOOK_INIT(file_open, hook_file_open),
 	LSM_HOOK_INIT(file_truncate, hook_file_truncate),
+
+	LSM_HOOK_INIT(getprocattr, landlock_getprocattr),
 };
 
 __init void landlock_add_fs_hooks(void)
-- 
2.39.2.722.g9855ee24e9-goog