In the Linux kernel, the following vulnerability has been resolved:
net/nfc: fix use-after-free llcp_sock_bind/connect
Commits 8a4cd82d (nfc: fix refcount leak in llcp_sock_connect()) and c33b1cc62 (nfc: fix refcount leak in llcp_sock_bind()) fixed a refcount leak bug in bind/connect but introduced a use-after-free if the same local is assigned to 2 different sockets.
This can be triggered by the following simple program: int sock1 = socket( AF_NFC, SOCK_STREAM, NFC_SOCKPROTO_LLCP ); int sock2 = socket( AF_NFC, SOCK_STREAM, NFC_SOCKPROTO_LLCP ); memset( &addr, 0, sizeof(struct sockaddr_nfc_llcp) ); addr.sa_family = AF_NFC; addr.nfc_protocol = NFC_PROTO_NFC_DEP; bind( sock1, (struct sockaddr*) &addr, sizeof(struct sockaddr_nfc_llcp) ) bind( sock2, (struct sockaddr*) &addr, sizeof(struct sockaddr_nfc_llcp) ) close(sock1); close(sock2);
Fix this by assigning NULL to llcp_sock->local after calling nfc_llcp_local_put.
This addresses CVE-2021-23134.