[PATCH 4.9 49/80] audit: check the length of userspace generated audit records

[Greg Kroah-Hartman]

From: Paul Moore <paul@xxxxxxxxxxxxxx>

commit 763dafc520add02a1f4639b500c509acc0ea8e5b upstream.

Commit 756125289285 ("audit: always check the netlink payload length
in audit_receive_msg()") fixed a number of missing message length
checks, but forgot to check the length of userspace generated audit
records.  The good news is that you need CAP_AUDIT_WRITE to submit
userspace audit records, which is generally only given to trusted
processes, so the impact should be limited.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 756125289285 ("audit: always check the netlink payload length in audit_receive_msg()")
Reported-by: syzbot+49e69b4d71a420ceda3e@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/audit.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -941,6 +941,9 @@ static int audit_receive_msg(struct sk_b
 	case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
 		if (!audit_enabled && msg_type != AUDIT_USER_AVC)
 			return 0;
+		/* exit early if there isn't at least one character to print */
+		if (data_len < 2)
+			return -EINVAL;
 
 		err = audit_filter(msg_type, AUDIT_FILTER_USER);
 		if (err == 1) { /* match or error */