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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+399c44bf1f43b8747403@syzkaller.appspotmail.com,
        syzbot+e4b12d8d202701f08b6d@syzkaller.appspotmail.com,
        Paul Moore <paul@paul-moore.com>
Subject: [PATCH 5.4 072/152] audit: always check the netlink payload length in audit_receive_msg()
Date:   Tue,  3 Mar 2020 18:42:50 +0100
Message-Id: <20200303174310.652084222@linuxfoundation.org>
In-Reply-To: <20200303174302.523080016@linuxfoundation.org>
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From: Paul Moore <paul@paul-moore.com>

commit 756125289285f6e55a03861bf4b6257aa3d19a93 upstream.

This patch ensures that we always check the netlink payload length
in audit_receive_msg() before we take any action on the payload
itself.

Cc: stable@vger.kernel.org
Reported-by: syzbot+399c44bf1f43b8747403@syzkaller.appspotmail.com
Reported-by: syzbot+e4b12d8d202701f08b6d@syzkaller.appspotmail.com
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/audit.c |   40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1100,13 +1100,11 @@ static void audit_log_feature_change(int
 	audit_log_end(ab);
 }
 
-static int audit_set_feature(struct sk_buff *skb)
+static int audit_set_feature(struct audit_features *uaf)
 {
-	struct audit_features *uaf;
 	int i;
 
 	BUILD_BUG_ON(AUDIT_LAST_FEATURE + 1 > ARRAY_SIZE(audit_feature_names));
-	uaf = nlmsg_data(nlmsg_hdr(skb));
 
 	/* if there is ever a version 2 we should handle that here */
 
@@ -1174,6 +1172,7 @@ static int audit_receive_msg(struct sk_b
 {
 	u32			seq;
 	void			*data;
+	int			data_len;
 	int			err;
 	struct audit_buffer	*ab;
 	u16			msg_type = nlh->nlmsg_type;
@@ -1187,6 +1186,7 @@ static int audit_receive_msg(struct sk_b
 
 	seq  = nlh->nlmsg_seq;
 	data = nlmsg_data(nlh);
+	data_len = nlmsg_len(nlh);
 
 	switch (msg_type) {
 	case AUDIT_GET: {
@@ -1210,7 +1210,7 @@ static int audit_receive_msg(struct sk_b
 		struct audit_status	s;
 		memset(&s, 0, sizeof(s));
 		/* guard against past and future API changes */
-		memcpy(&s, data, min_t(size_t, sizeof(s), nlmsg_len(nlh)));
+		memcpy(&s, data, min_t(size_t, sizeof(s), data_len));
 		if (s.mask & AUDIT_STATUS_ENABLED) {
 			err = audit_set_enabled(s.enabled);
 			if (err < 0)
@@ -1314,7 +1314,9 @@ static int audit_receive_msg(struct sk_b
 			return err;
 		break;
 	case AUDIT_SET_FEATURE:
-		err = audit_set_feature(skb);
+		if (data_len < sizeof(struct audit_features))
+			return -EINVAL;
+		err = audit_set_feature(data);
 		if (err)
 			return err;
 		break;
@@ -1326,6 +1328,8 @@ static int audit_receive_msg(struct sk_b
 
 		err = audit_filter(msg_type, AUDIT_FILTER_USER);
 		if (err == 1) { /* match or error */
+			char *str = data;
+
 			err = 0;
 			if (msg_type == AUDIT_USER_TTY) {
 				err = tty_audit_push();
@@ -1333,26 +1337,24 @@ static int audit_receive_msg(struct sk_b
 					break;
 			}
 			audit_log_user_recv_msg(&ab, msg_type);
-			if (msg_type != AUDIT_USER_TTY)
+			if (msg_type != AUDIT_USER_TTY) {
+				/* ensure NULL termination */
+				str[data_len - 1] = '\0';
 				audit_log_format(ab, " msg='%.*s'",
 						 AUDIT_MESSAGE_TEXT_MAX,
-						 (char *)data);
-			else {
-				int size;
-
+						 str);
+			} else {
 				audit_log_format(ab, " data=");
-				size = nlmsg_len(nlh);
-				if (size > 0 &&
-				    ((unsigned char *)data)[size - 1] == '\0')
-					size--;
-				audit_log_n_untrustedstring(ab, data, size);
+				if (data_len > 0 && str[data_len - 1] == '\0')
+					data_len--;
+				audit_log_n_untrustedstring(ab, str, data_len);
 			}
 			audit_log_end(ab);
 		}
 		break;
 	case AUDIT_ADD_RULE:
 	case AUDIT_DEL_RULE:
-		if (nlmsg_len(nlh) < sizeof(struct audit_rule_data))
+		if (data_len < sizeof(struct audit_rule_data))
 			return -EINVAL;
 		if (audit_enabled == AUDIT_LOCKED) {
 			audit_log_common_recv_msg(audit_context(), &ab,
@@ -1364,7 +1366,7 @@ static int audit_receive_msg(struct sk_b
 			audit_log_end(ab);
 			return -EPERM;
 		}
-		err = audit_rule_change(msg_type, seq, data, nlmsg_len(nlh));
+		err = audit_rule_change(msg_type, seq, data, data_len);
 		break;
 	case AUDIT_LIST_RULES:
 		err = audit_list_rules_send(skb, seq);
@@ -1379,7 +1381,7 @@ static int audit_receive_msg(struct sk_b
 	case AUDIT_MAKE_EQUIV: {
 		void *bufp = data;
 		u32 sizes[2];
-		size_t msglen = nlmsg_len(nlh);
+		size_t msglen = data_len;
 		char *old, *new;
 
 		err = -EINVAL;
@@ -1455,7 +1457,7 @@ static int audit_receive_msg(struct sk_b
 
 		memset(&s, 0, sizeof(s));
 		/* guard against past and future API changes */
-		memcpy(&s, data, min_t(size_t, sizeof(s), nlmsg_len(nlh)));
+		memcpy(&s, data, min_t(size_t, sizeof(s), data_len));
 		/* check if new data is valid */
 		if ((s.enabled != 0 && s.enabled != 1) ||
 		    (s.log_passwd != 0 && s.log_passwd != 1))