apparmor: support querying extended trusted helper extra data

Allow a profile to carry extra data that can be queried via userspace.
This provides a means to store extra data in a profile that a trusted
helper can extract and use from live policy.

Signed-off-by: William Hua <william.hua@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

1 files changed, 139 insertions, 0 deletions

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 7613a28f157e..6834000640d7 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -213,6 +213,144 @@ static const struct file_operations aa_fs_profile_remove = {
 	.llseek = default_llseek,
 };
 
+/**
+ * query_data - queries a policy and writes its data to buf
+ * @buf: the resulting data is stored here (NOT NULL)
+ * @buf_len: size of buf
+ * @query: query string used to retrieve data
+ * @query_len: size of query including second NUL byte
+ *
+ * The buffers pointed to by buf and query may overlap. The query buffer is
+ * parsed before buf is written to.
+ *
+ * The query should look like "<LABEL>\0<KEY>\0", where <LABEL> is the name of
+ * the security confinement context and <KEY> is the name of the data to
+ * retrieve. <LABEL> and <KEY> must not be NUL-terminated.
+ *
+ * Don't expect the contents of buf to be preserved on failure.
+ *
+ * Returns: number of characters written to buf or -errno on failure
+ */
+static ssize_t query_data(char *buf, size_t buf_len,
+			  char *query, size_t query_len)
+{
+	char *out;
+	const char *key;
+	struct aa_profile *profile;
+	struct aa_data *data;
+	u32 bytes, blocks;
+	__le32 outle32;
+
+	if (!query_len)
+		return -EINVAL; /* need a query */
+
+	key = query + strnlen(query, query_len) + 1;
+	if (key + 1 >= query + query_len)
+		return -EINVAL; /* not enough space for a non-empty key */
+	if (key + strnlen(key, query + query_len - key) >= query + query_len)
+		return -EINVAL; /* must end with NUL */
+
+	if (buf_len < sizeof(bytes) + sizeof(blocks))
+		return -EINVAL; /* not enough space */
+
+	profile = aa_current_profile();
+
+	/* We are going to leave space for two numbers. The first is the total
+	 * number of bytes we are writing after the first number. This is so
+	 * users can read the full output without reallocation.
+	 *
+	 * The second number is the number of data blocks we're writing. An
+	 * application might be confined by multiple policies having data in
+	 * the same key.
+	 */
+	memset(buf, 0, sizeof(bytes) + sizeof(blocks));
+	out = buf + sizeof(bytes) + sizeof(blocks);
+
+	blocks = 0;
+	if (profile->data) {
+		data = rhashtable_lookup_fast(profile->data, &key,
+					      profile->data->p);
+
+		if (data) {
+			if (out + sizeof(outle32) + data->size > buf + buf_len)
+				return -EINVAL; /* not enough space */
+			outle32 = __cpu_to_le32(data->size);
+			memcpy(out, &outle32, sizeof(outle32));
+			out += sizeof(outle32);
+			memcpy(out, data->data, data->size);
+			out += data->size;
+			blocks++;
+		}
+	}
+
+	outle32 = __cpu_to_le32(out - buf - sizeof(bytes));
+	memcpy(buf, &outle32, sizeof(outle32));
+	outle32 = __cpu_to_le32(blocks);
+	memcpy(buf + sizeof(bytes), &outle32, sizeof(outle32));
+
+	return out - buf;
+}
+
+#define QUERY_CMD_DATA		"data\0"
+#define QUERY_CMD_DATA_LEN	5
+
+/**
+ * aa_write_access - generic permissions and data query
+ * @file: pointer to open apparmorfs/access file
+ * @ubuf: user buffer containing the complete query string (NOT NULL)
+ * @count: size of ubuf
+ * @ppos: position in the file (MUST BE ZERO)
+ *
+ * Allows for one permissions or data query per open(), write(), and read()
+ * sequence. The only queries currently supported are label-based queries for
+ * permissions or data.
+ *
+ * For permissions queries, ubuf must begin with "label\0", followed by the
+ * profile query specific format described in the query_label() function
+ * documentation.
+ *
+ * For data queries, ubuf must have the form "data\0<LABEL>\0<KEY>\0", where
+ * <LABEL> is the name of the security confinement context and <KEY> is the
+ * name of the data to retrieve.
+ *
+ * Returns: number of bytes written or -errno on failure
+ */
+static ssize_t aa_write_access(struct file *file, const char __user *ubuf,
+			       size_t count, loff_t *ppos)
+{
+	char *buf;
+	ssize_t len;
+
+	if (*ppos)
+		return -ESPIPE;
+
+	buf = simple_transaction_get(file, ubuf, count);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	if (count > QUERY_CMD_DATA_LEN &&
+		   !memcmp(buf, QUERY_CMD_DATA, QUERY_CMD_DATA_LEN)) {
+		len = query_data(buf, SIMPLE_TRANSACTION_LIMIT,
+				 buf + QUERY_CMD_DATA_LEN,
+				 count - QUERY_CMD_DATA_LEN);
+	} else
+		len = -EINVAL;
+
+	if (len < 0)
+		return len;
+
+	simple_transaction_set(file, len);
+
+	return count;
+}
+
+static const struct file_operations aa_fs_access = {
+	.write		= aa_write_access,
+	.read		= simple_transaction_read,
+	.release	= simple_transaction_release,
+	.llseek		= generic_file_llseek,
+};
+
 static int aa_fs_seq_show(struct seq_file *seq, void *v)
 {
 	struct aa_fs_entry *fs_file = seq->private;
@@ -1078,6 +1216,7 @@ static struct aa_fs_entry aa_fs_entry_features[] = {
 };
 
 static struct aa_fs_entry aa_fs_entry_apparmor[] = {
+	AA_FS_FILE_FOPS(".access", 0640, &aa_fs_access),
 	AA_FS_FILE_FOPS(".ns_level", 0666, &aa_fs_ns_level),
 	AA_FS_FILE_FOPS(".ns_name", 0640, &aa_fs_ns_name),
 	AA_FS_FILE_FOPS("profiles", 0440, &aa_fs_profiles_fops),