irda: Only insert new objects into the global database via setsockopt

The irda_setsockopt() function conditionally allocates memory for a new
self->ias_object or, in some cases, reuses the existing
self->ias_object. Existing objects were incorrectly reinserted into the
LM_IAS database which corrupted the doubly linked list used for the
hashbin implementation of the LM_IAS database. When combined with a
memory leak in irda_bind(), this issue could be leveraged to create a
use-after-free vulnerability in the hashbin list. This patch fixes the
issue by only inserting newly allocated objects into the database.

CVE-2018-6555

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Reviewed-by: Seth Arnold <seth.arnold@canonical.com>
Reviewed-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/irda/af_irda.c

@@ -2023,7 +2023,11 @@ static int irda_setsockopt(struct socket *sock, int level, int optname,
 			err = -EINVAL;
 			goto out;
 		}
+
+		/* Only insert newly allocated objects */
+		if (free_ias)
 			irias_insert_object(ias_obj);
+
 		kfree(ias_opt);
 		break;
 	case IRLMP_IAS_DEL: