{"id":109152,"date":"2020-10-15T21:09:11","date_gmt":"2020-10-16T04:09:11","guid":{"rendered":"https:\/\/unit42.paloaltonetworks.com\/?p=109152"},"modified":"2020-10-15T21:17:11","modified_gmt":"2020-10-16T04:17:11","slug":"cve-2020-14386","status":"publish","type":"post","link":"https:\/\/unit42.paloaltonetworks.com\/ja\/cve-2020-14386\/","title":{"rendered":"CVE-2020-14386: Linux\u30ab\u30fc\u30cd\u30eb\u306e\u6a29\u9650\u6607\u683c\u306e\u8106\u5f31\u6027"},"content":{"rendered":"

\u6982\u8981<\/h2>\n

\u3053\u306e\u3068\u3053\u308d\u3001\u79c1\u306fLinux\u30ab\u30fc\u30cd\u30eb\u306e\u30d1\u30b1\u30c3\u30c8\u30bd\u30b1\u30c3\u30c8\u306e\u30bd\u30fc\u30b9\u30b3\u30fc\u30c9\u306e\u76e3\u67fb\u306b\u6642\u9593\u3092\u6ce8\u3044\u3067\u3044\u307e\u3057\u305f\u3002\u3053\u308c\u306f\u3001Linux\u30ab\u30fc\u30cd\u30eb\u306e\u30e1\u30e2\u30ea\u7834\u640d\u306e\u8106\u5f31\u6027\u3067\u3042\u308bCVE-2020-14386<\/a>\u306e\u767a\u898b\u306b\u3064\u306a\u304c\u308a\u307e\u3057\u305f\u3002\u3053\u306e\u3088\u3046\u306a\u8106\u5f31\u6027\u3092\u5229\u7528\u3059\u308b\u3053\u3068\u306b\u3088\u308a\u3001Linux\u30b7\u30b9\u30c6\u30e0\u3067\u3001\u6a29\u9650\u306e\u306a\u3044\u30e6\u30fc\u30b6\u30fc\u306e\u6a29\u9650\u3092\u30eb\u30fc\u30c8\u30e6\u30fc\u30b6\u30fc\u306e\u6a29\u9650\u306b\u6607\u683c\u3067\u304d\u307e\u3059\u3002\u672c\u7a3f\u3067\u306f\u3001\u3053\u306e\u8106\u5f31\u6027\u306e\u6280\u8853\u7684\u89e3\u8aac\u3001\u305d\u306e\u60aa\u7528\u65b9\u6cd5\u3001\u305d\u3057\u3066\u30d1\u30ed\u30a2\u30eb\u30c8\u30cd\u30c3\u30c8\u30ef\u30fc\u30af\u30b9\u306e\u304a\u5ba2\u69d8\u304c\u3069\u306e\u3088\u3046\u306b\u4fdd\u8b77\u3055\u308c\u3066\u3044\u308b\u304b\u306b\u3064\u3044\u3066\u8aac\u660e\u3057\u307e\u3059\u3002<\/p>\n

\u6570\u5e74\u524d\u3001\u30d1\u30b1\u30c3\u30c8\u30bd\u30b1\u30c3\u30c8\u3067\u3044\u304f\u3064\u304b\u306e\u8106\u5f31\u6027\u304c\u767a\u898b\u3055\u308c(CVE-2017-7308<\/a>\u304a\u3088\u3073CVE-2016-8655<\/a>)\u3001\u305d\u306e\u4e3b\u8981\u306a\u6a5f\u80fd\u306e\u6982\u8981\u3092\u793a\u3057\u305f\u3001Project Zero\u306e\u30d6\u30ed\u30b0<\/a>\u3084Openwall<\/a>\u306a\u3069\u306e\u8a18\u4e8b\u304c\u516c\u958b\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n

\u5177\u4f53\u7684\u306b\u3044\u3048\u3070\u3001\u3053\u306e\u8106\u5f31\u6027\u3092\u30c8\u30ea\u30ac\u30fc\u3059\u308b\u306b\u306f\u3001\u30ab\u30fc\u30cd\u30eb\u3067AF_PACKET<\/span>\u30bd\u30b1\u30c3\u30c8\u304c\u6709\u52b9\u306b\u306a\u3063\u3066\u3044\u308b\u3053\u3068(CONFIG_PACKET=y<\/span>)\u306b\u304f\u308f\u3048\u3001\u30c8\u30ea\u30ac\u30fc\u3068\u306a\u308b\u30d7\u30ed\u30bb\u30b9\u306bCAP_NET_RAW<\/span>\u6a29\u9650\u304c\u306a\u3051\u308c\u3070\u3044\u3051\u307e\u305b\u3093\u3002CAP_NET_RAW<\/span>\u6a29\u9650\u306f\u3001\u30e6\u30fc\u30b6\u30fc\u540d\u524d\u7a7a\u9593\u304c\u6709\u52b9\u3067(CONFIG_USER_NS=y<\/span>)\u3001\u6a29\u9650\u306e\u306a\u3044\u30e6\u30fc\u30b6\u30fc\u304b\u3089\u3082\u30a2\u30af\u30bb\u30b9\u53ef\u80fd\u3067\u3042\u308c\u3070\u3001\u6a29\u9650\u306e\u306a\u3044\u30e6\u30fc\u30b6\u30fc\u306e\u540d\u524d\u7a7a\u9593\u3067\u3082\u53d6\u5f97\u3067\u304d\u307e\u3059\u3002\u9a5a\u304f\u3053\u3068\u306b\u3001\u3053\u308c\u3089\u306e\u5236\u7d04\u306f\u3001Ubuntu\u306a\u3069\u306e\u4e00\u90e8\u306e\u30c7\u30a3\u30b9\u30c8\u30ea\u30d3\u30e5\u30fc\u30b7\u30e7\u30f3\u3067\u306f\u30c7\u30d5\u30a9\u30eb\u30c8\u3067\u6e80\u305f\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n

\u30d1\u30ed\u30a2\u30eb\u30c8\u30cd\u30c3\u30c8\u30ef\u30fc\u30af\u30b9\u306eCortex XDR\u3092\u3054\u5229\u7528\u4e2d\u306e\u304a\u5ba2\u69d8\u306f\u3053\u306e\u4e0d\u5177\u5408\u306e\u60aa\u7528\u3092\u963b\u6b62\u3067\u304d\u307e\u3059\u3002\u3053\u308c\u306b\u306f\u3001\u4e00\u9023\u306e\u30a4\u30d9\u30f3\u30c8\u5168\u4f53\u306b\u308f\u305f\u308a\u60aa\u610f\u306e\u3042\u308b\u632f\u308b\u821e\u3044\u3092\u76e3\u8996\u3057\u3001\u653b\u6483\u691c\u51fa\u5f8c\u305f\u3060\u3061\u306b\u4e2d\u65ad\u3055\u305b\u308bBehavioral Threat Protection<\/a> (BTP) (\u632f\u308b\u821e\u3044\u30d9\u30fc\u30b9\u306e\u8105\u5a01\u9632\u5fa1)\u6a5f\u80fd\u3068\u3001Local Privilege Escalation Protection<\/a> (\u30ed\u30fc\u30ab\u30eb\u6a29\u9650\u6607\u683c\u9632\u5fa1)\u30e2\u30b8\u30e5\u30fc\u30eb\u304c\u7d44\u307f\u5408\u308f\u305b\u3066\u4f7f\u308f\u308c\u307e\u3059\u3002<\/p>\n

\u6280\u8853\u7684\u8a73\u7d30<\/h2>\n

(\u3053\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u306e\u3059\u3079\u3066\u306e\u30b3\u30fc\u30c9\u306e\u56f3\u306f\u30d0\u30fc\u30b8\u30e7\u30f35.7\u306e\u30ab\u30fc\u30cd\u30eb\u30bd\u30fc\u30b9\u304b\u3089\u306e\u3082\u306e\u3067\u3059\u3002)<\/p>\n

AF_PACKET<\/span>\u30bd\u30b1\u30c3\u30c8\u306e\u5b9f\u88c5\u306b\u3064\u3044\u3066\u306fProject Zero\u30d6\u30ed\u30b0\u3067\u8a73\u3057\u304f\u8aac\u660e\u3057\u3066\u3044\u307e\u3059\u306e\u3067\u3001\u3053\u3053\u3067\u306f\u305d\u3061\u3089\u306e\u8a18\u4e8b\u3067\u89e3\u8aac\u6e08\u307f\u306e\u5185\u5bb9\uff08\u30d5\u30ec\u30fc\u30e0\u3068\u30d6\u30ed\u30c3\u30af\u306e\u95a2\u4fc2\u306a\u3069\uff09\u306b\u3064\u3044\u3066\u306f\u5272\u611b\u3057\u3001\u3055\u3063\u305d\u304f\u8106\u5f31\u6027\u3068\u305d\u306e\u6839\u672c\u539f\u56e0\u306e\u8aac\u660e\u306b\u5165\u308a\u305f\u3044\u3068\u601d\u3044\u307e\u3059\u3002<\/p>\n

\u3053\u306e\u4e0d\u5177\u5408\u306f\u3001\u30e1\u30e2\u30ea\u306e\u7834\u640d\u306b\u3064\u306a\u304c\u308b\u6f14\u7b97\u306e\u554f\u984c\u306b\u7aef\u3092\u767a\u3057\u3066\u3044\u307e\u3059\u3002\u3053\u306e\u6f14\u7b97\u306e\u554f\u984c\u306f\u3001net\/packet\/af_packet.c<\/span>\u5185\u306etpacket_rcv<\/span>\u95a2\u6570\u306b\u3042\u308a\u307e\u3059\u3002<\/p>\n

\u3053\u306e\u6f14\u7b97\u306e\u4e0d\u5177\u5408\u306f2008\u5e747\u670819\u65e5\u306b\u3001\u30b3\u30df\u30c3\u30c88913336<\/a> (\u201cpacket: add PACKET_RESERVE sockopt<\/span>\u201d)\u3067\u5c0e\u5165\u3055\u308c\u307e\u3057\u305f\u3002\u305f\u3060\u3057\u3001\u30e1\u30e2\u30ea\u7834\u640d\u3092\u5f15\u304d\u8d77\u3053\u3059\u3088\u3046\u306a\u30c8\u30ea\u30ac\u30fc\u53ef\u80fd\u306b\u306a\u3063\u305f\u306e\u306f\u30012016\u5e742\u6708\u306e\u30b3\u30df\u30c3\u30c858d19b19cd99 (\u201cpacket: vnet_hdr <\/span>support for tpacket_rcv<\/span>\u201c)\u304b\u3089\u3067\u3059\u30022017\u5e745\u6708\u306e\u30b3\u30df\u30c3\u30c8bcc536 (\u201cnet\/packet: fix overflow in check for tp_reserve<\/span>\u201d)\u3084\u30012017\u5e748\u6708\u306e\u30b3\u30df\u30c3\u30c8edb58be (\u201cpacket: Don\u2019t write vnet header beyond end of buffer\u201d)<\/span>\u306a\u3069\u3067\u4f55\u5ea6\u304b\u4fee\u6b63\u304c\u8a66\u307f\u3089\u308c\u307e\u3057\u305f\u304c\u3001\u3044\u305a\u308c\u3082\u30e1\u30e2\u30ea\u7834\u640d\u3092\u5341\u5206\u9632\u3050\u3053\u3068\u304c\u3067\u304d\u307e\u305b\u3093\u3067\u3057\u305f\u3002<\/p>\n

\u307e\u305a\u3001PACKET_RESERVE<\/span>\u30aa\u30d7\u30b7\u30e7\u30f3\u304b\u3089\u898b\u3066\u3044\u304d\u307e\u3057\u3087\u3046\u3002\u3053\u306e\u8106\u5f31\u6027\u3092\u30c8\u30ea\u30ac\u30fc\u3059\u308b\u306b\u306f\u3001raw\u30bd\u30b1\u30c3\u30c8(domain \u306b AF_PACKET<\/span>\u3001type \u306b SOCK_RAW<\/span>\u3092\u6307\u5b9a)\u3067\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u306bTPACKET_V2<\/span>\u3092\u6307\u5b9a\u3057\u3001<\/span>PACKET_RESERVE<\/span>\u30aa\u30d7\u30b7\u30e7\u30f3\u306b\u7279\u5b9a\u306e\u5024\u3092\u6307\u5b9a\u3057\u3066\u4f5c\u6210\u3059\u308b\u5fc5\u8981\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n

\"PACKET_RESERVE
\u51fa\u5178: https:\/\/man7.org\/linux\/man-pages\/man7\/packet.7.html<\/a><\/figcaption><\/figure>\n

\u3053\u306e\u30de\u30cb\u30e5\u30a2\u30eb\u3067\u8a00\u53ca\u3055\u308c\u3066\u3044\u308b\u300cadditional headroom\uff08\u30d1\u30b1\u30c3\u30c8\u524d\u306e\u8ffd\u52a0\u9818\u57df\uff09\u300d\u306f\u5358\u306b\u30e6\u30fc\u30b6\u30fc\u304c\u6307\u5b9a\u3057\u305f\u30b5\u30a4\u30ba\u306e\u30d0\u30c3\u30d5\u30a1\u306e\u3053\u3068\u3067\u3001\u3053\u306e\u5272\u308a\u5f53\u3066\u304c\u884c\u308f\u308c\u305f\u5f8c\u3067\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u306e\u5404\u30d1\u30b1\u30c3\u30c8\u306e\u5b9f\u30c7\u30fc\u30bf\u304c\u53d7\u4fe1\u3055\u308c\u307e\u3059\u3002\u3053\u306e\u5024\u306f\u30e6\u30fc\u30b6\u30fc\u7a7a\u9593\u304b\u3089setsockopt<\/span>\u30b7\u30b9\u30c6\u30e0\u30b3\u30fc\u30eb\u3067\u8a2d\u5b9a\u3067\u304d\u307e\u3059\u3002<\/p>\n

case PACKET_RESERVE:\r\n    {\r\n        unsigned int val;\r\n        if (optlen != sizeof(val))\r\n            return -EINVAL;\r\n        if (copy_from_user(&val, optval, sizeof(val)))\r\n            return -EFAULT;\r\n        if (val > INT_MAX)\r\n            return -EINVAL;\r\n        lock_sock(sk);\r\n        if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {\r\n            ret = -EBUSY;\r\n        } else {\r\n            po->tp_reserve = val;\r\n            ret = 0;\r\n        }\r\n        release_sock(sk);\r\n        return ret;\r\n    }<\/pre>\n
\u56f31. setsockopt \u2013 PACKET_RESERVE\u306e\u5b9f\u88c5<\/em><\/span><\/p>\n
\u56f31\u306b\u793a\u3059\u3088\u3046\u306b\u3001\u6700\u521d\u306b\u3001\u5024\u304cINT_MAX<\/span>\u3088\u308a\u5c0f\u3055\u3044\u304b\u3069\u3046\u304b\u306e\u30c1\u30a7\u30c3\u30af\u304c\u3042\u308a\u307e\u3059\u3002\u3053\u306e\u30c1\u30a7\u30c3\u30af\u306f\u3001packet_set_ring<\/span>\u3067\u306e\u6700\u5c0f\u30d5\u30ec\u30fc\u30e0\u30b5\u30a4\u30ba\u306e\u8a08\u7b97\u3067\u306e\u30aa\u30fc\u30d0\u30fc\u30d5\u30ed\u30fc\u3092\u9632\u6b62\u3059\u308b\u305f\u3081\u306b\u3001\u3053\u306e\u30d1\u30c3\u30c1<\/a>\u3067\u8ffd\u52a0\u3055\u308c\u305f\u3082\u306e\u3067\u3059\u3002\u305d\u306e\u5f8c\u3001\u53d7\u4fe1\/\u9001\u4fe1\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u306b\u30da\u30fc\u30b8\u304c\u5272\u308a\u5f53\u3066\u3089\u308c\u3066\u3044\u306a\u3044\u3053\u3068\u304c\u78ba\u8a8d\u3055\u308c\u307e\u3059\u3002\u3053\u308c\u306f\u3001tp_reserve<\/span>\u30d5\u30a3\u30fc\u30eb\u30c9\u3068\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u81ea\u4f53\u306e\u9593\u3067\u77db\u76fe\u304c\u767a\u751f\u3057\u306a\u3044\u3088\u3046\u306b\u5b9f\u884c\u3055\u308c\u307e\u3059\u3002
\ntp_reserve<\/span>\u306b\u5024\u3092\u8a2d\u5b9a\u5f8c\u3001optname<\/span>\u306b<\/span>PACKET_RX_RING<\/span>\u3092\u6307\u5b9a\u3057\u305fsetsockopt<\/span>\u30b7\u30b9\u30c6\u30e0\u30b3\u30fc\u30eb\u306b\u3088\u308a\u3001\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u81ea\u4f53\u306e\u5272\u308a\u5f53\u3066\u3092\u30c8\u30ea\u30ac\u30fc\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n
Create a memory-mapped ring buffer for asynchronous packet reception.(\u975e\u540c\u671f\u3067\u306e\u30d1\u30b1\u30c3\u30c8\u53d7\u4fe1\u7528\u306e\u30e1\u30e2\u30ea\u30de\u30c3\u30d7\u3055\u308c\u305f\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u3092\u4f5c\u6210\u3059\u308b\u3002)<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u56f32. \u30de\u30cb\u30e5\u30a2\u30eb<\/a>\u306e packet \u2013 PACKET_RX_RING<\/span>\u30aa\u30d7\u30b7\u30e7\u30f3\u304b\u3089<\/em><\/span><\/p>\n
\u3053\u308c\u306fpacket_set_ring<\/span>\u95a2\u6570\u306b\u5b9f\u88c5\u3055\u308c\u3066\u3044\u307e\u3059\u3002\u6700\u521d\u306b\u3001\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u5272\u308a\u5f53\u3066\u524d\u306b\u3001\u30e6\u30fc\u30b6\u30fc\u7a7a\u9593\u304b\u3089\u53d7\u3051\u53d6\u3063\u305ftpacket_req<\/span>\u69cb\u9020\u4f53\u306b\u5bfe\u3057\u3001\u3044\u304f\u3064\u304b\u306e\u6f14\u7b97\u30c1\u30a7\u30c3\u30af\u304c\u5b9f\u884c\u3055\u308c\u307e\u3059\u3002<\/p>\n
min_frame_size = po->tp_hdrlen + po->tp_reserve;\r\n\u2026\r\n\u2026\r\nif (unlikely(req->tp_frame_size < min_frame_size))\r\n     goto out;<\/pre>\n
\u56f33. packet_set_ring<\/span>\u95a2\u6570\u306e\u30b5\u30cb\u30c6\u30a3\u30c1\u30a7\u30c3\u30af\u306e\u4e00\u90e8<\/em><\/span><\/p>\n
\u56f33\u306b\u793a\u3059\u3088\u3046\u306b\u3001\u307e\u305a\u6700\u5c0f\u30d5\u30ec\u30fc\u30e0\u30b5\u30a4\u30ba\u304c\u8a08\u7b97\u3055\u308c\u3001\u6b21\u306b\u30e6\u30fc\u30b6\u30fc\u7a7a\u9593\u304b\u3089\u53d7\u3051\u53d6\u3063\u305f\u5024\u3068\u6bd4\u8f03\u3057\u3066\u691c\u8a3c\u3055\u308c\u307e\u3059\u3002\u3053\u306e\u30c1\u30a7\u30c3\u30af\u306b\u3088\u308a\u3001tpacket<\/span>\u30d8\u30c3\u30c0\u30fc\u69cb\u9020\u4f53(\u5bfe\u5fdc\u3059\u308b\u30d0\u30fc\u30b8\u30e7\u30f3\u306b\u5bfe\u3059\u308b)\u304a\u3088\u3073tp_reserve<\/span>\u306e\u30d0\u30a4\u30c8\u6570\u306b\u5bfe\u3059\u308b\u5341\u5206\u306a\u30b9\u30da\u30fc\u30b9\u304c\u5404\u30d5\u30ec\u30fc\u30e0\u306b\u3042\u308b\u3053\u3068\u304c\u78ba\u8a8d\u3055\u308c\u307e\u3059\u3002
\n\u305d\u306e\u5f8c\u3001\u3059\u3079\u3066\u306e\u30b5\u30cb\u30c6\u30a3\u30c1\u30a7\u30c3\u30af\u306e\u5b9f\u884c\u5f8c\u3001alloc_pg_vec<\/span>\u3078\u306e\u30b3\u30fc\u30eb\u306b\u3088\u308a\u3001\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u81ea\u4f53\u304c\u5272\u308a\u5f53\u3066\u3089\u308c\u307e\u3059\u3002<\/p>\n
order = get_order(req->tp_block_size);\r\npg_vec = alloc_pg_vec(req, order);<\/pre>\n
\u56f34.packet_set_ring<\/span>\u95a2\u6570\u5185\u3067\u306e\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u5272\u308a\u5f53\u3066\u95a2\u6570\u306e\u547c\u3073\u51fa\u3057<\/em><\/span><\/p>\n
\u4e0a\u306e\u56f3\u306b\u793a\u3059\u3088\u3046\u306b\u3001\u30d6\u30ed\u30c3\u30af\u30b5\u30a4\u30ba\u306f\u30e6\u30fc\u30b6\u30fc\u7a7a\u9593\u304b\u3089\u5236\u5fa1\u3055\u308c\u307e\u3059\u3002alloc_pg_vec<\/span>\u95a2\u6570\u306fpg_vec<\/span>\u914d\u5217\u3092\u5272\u308a\u5f53\u3066\u3066\u304b\u3089\u3001alloc_one_pg_vec_page<\/span>\u95a2\u6570\u306b\u3088\u308a\u5404\u30d6\u30ed\u30c3\u30af\u3092\u5272\u308a\u5f53\u3066\u307e\u3059\u3002<\/p>\n
static struct pgv *alloc_pg_vec(struct tpacket_req *req, int order)\r\n    {\r\n        unsigned int block_nr = req->tp_block_nr;\r\n        struct pgv *pg_vec;\r\n        int i;\r\n        pg_vec = kcalloc(block_nr, sizeof(struct pgv), GFP_KERNEL | __GFP_NOWARN);\r\n        if (unlikely(!pg_vec))\r\n            goto out;\r\n        for (i = 0; i < block_nr; i++) {\r\n            pg_vec[i].buffer = alloc_one_pg_vec_page(order);<\/pre>\n
\u56f35. alloc_pg_vec<\/span>\u306e\u5b9f\u88c5<\/em><\/span><\/p>\n
alloc_one_pg_vec_page<\/span>\u95a2\u6570\u306f\u3001\u30d6\u30ed\u30c3\u30af\u30da\u30fc\u30b8\u3092\u5272\u308a\u5f53\u3066\u308b\u305f\u3081\u306b__get_free_pages<\/span>\u3092\u4f7f\u7528\u3057\u307e\u3059\u3002<\/p>\n
static char *alloc_one_pg_vec_page(unsigned long order)\r\n    {\r\n        char *buffer;\r\n        gfp_t gfp_flags = GFP_KERNEL | __GFP_COMP |\r\n                          __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY;\r\n        buffer = (char *) __get_free_pages(gfp_flags, order);\r\n        if (buffer)\r\n            return buffer;<\/pre>\n
\u56f36. alloc_one_pg_vec_page<\/span>\u306e\u5b9f\u88c5<\/em><\/span><\/p>\n
\u30d6\u30ed\u30c3\u30af\u306e\u5272\u308a\u5f53\u3066\u5f8c\u3001pg_vec<\/span>\u914d\u5217\u304c\u3001\u30bd\u30b1\u30c3\u30c8\u3092\u8868\u3059packet_sock<\/span>\u69cb\u9020\u4f53\u306b\u57cb\u3081\u8fbc\u307e\u308c\u3066\u3044\u308bpacket_ring_buffer<\/span>\u69cb\u9020\u4f53\u306b\u4fdd\u5b58\u3055\u308c\u307e\u3059\u3002
\n\u30a4\u30f3\u30bf\u30fc\u30d5\u30a7\u30a4\u30b9\u4e0a\u3067\u30d1\u30b1\u30c3\u30c8\u3092\u53d7\u4fe1\u3059\u308b\u3068\u3001tpacket_rcv<\/span>\u95a2\u6570\u306b\u30d0\u30a4\u30f3\u30c9\u3055\u308c\u3066\u3044\u308b\u30bd\u30b1\u30c3\u30c8\u304c\u547c\u3073\u51fa\u3055\u308c\u3001\u30d1\u30b1\u30c3\u30c8\u30c7\u30fc\u30bf\u304cTPACKET<\/span>\u30e1\u30bf\u30c7\u30fc\u30bf\u3068\u3068\u3082\u306b\u3001\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u306b\u66f8\u304d\u8fbc\u307e\u308c\u307e\u3059\u3002tcpdump\u306a\u3069\u306e\u5b9f\u969b\u306e\u7528\u9014\u3067\u306f\u3001\u3053\u306e\u30d0\u30c3\u30d5\u30a1\u306f\u30e6\u30fc\u30b6\u30fc\u7a7a\u9593\u306bmmap\u3055\u308c\u3001\u305d\u3053\u304b\u3089\u30d1\u30b1\u30c3\u30c8\u30c7\u30fc\u30bf\u3092\u8aad\u307f\u51fa\u3059\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
\u4e0d\u5177\u5408<\/h2>\n
\u6b21\u306f\u3001tpacket_rcv<\/span>\u95a2\u6570\u306e\u5b9f\u88c5(\u56f37)\u3092\u8a73\u3057\u304f\u898b\u3066\u3044\u304d\u307e\u3057\u3087\u3046\u3002\u307e\u305a\u3001\u53d7\u4fe1\u3057\u305f\u30d1\u30b1\u30c3\u30c8\u306e\u30cd\u30c3\u30c8\u30ef\u30fc\u30af\u30d8\u30c3\u30c0\u30fc\u306e\u30aa\u30d5\u30bb\u30c3\u30c8\u3092maclen<\/span>\u306b\u62bd\u51fa\u3059\u308b\u305f\u3081\u306b\u3001skb_network_offset<\/span>\u304c\u547c\u3073\u51fa\u3055\u308c\u307e\u3059\u3002\u3053\u306e\u4f8b\u3067\u306f\u3001\u30b5\u30a4\u30ba\u306fEthernet\u30d8\u30c3\u30c0\u30fc\u306e\u30b5\u30a4\u30ba\u3067\u3042\u308b14\u30d0\u30a4\u30c8\u3067\u3059\u3002\u305d\u306e\u5f8c\u3001TPACKET<\/span>\u30d8\u30c3\u30c0\u30fc(\u30d0\u30fc\u30b8\u30e7\u30f3\u3054\u3068\u306b\u56fa\u5b9a)\u3001maclen<\/span>\u3001\u304a\u3088\u3073tp_reserve<\/span>\u5024(\u30e6\u30fc\u30b6\u30fc\u5236\u5fa1)\u3092\u8003\u616e\u3057\u3066\u3001netoff(\u30d5\u30ec\u30fc\u30e0\u5185\u306e\u30cd\u30c3\u30c8\u30ef\u30fc\u30af\u30d8\u30c3\u30c0\u30fc\u306e\u30aa\u30d5\u30bb\u30c3\u30c8\u3092\u8868\u3059)\u304c\u8a08\u7b97\u3055\u308c\u307e\u3059\u3002<\/p>\n
\u305f\u3060\u3057\u3001tp_reserve<\/span>\u306e\u578b\u306funsigned<\/span> int<\/span>\u3001netoff<\/span>\u306e\u578b\u306funsigned<\/span> short<\/span>\u3067\u3001(\u524d\u8ff0\u306e\u3068\u304a\u308a)tp_reserve<\/span>\u306e\u5024\u306b\u5bfe\u3059\u308b\u552f\u4e00\u306e\u5236\u7d04\u306fINT_MAX<\/span>\u3088\u308a\u5c0f\u3055\u3044\u3053\u3068\u3067\u3042\u308b\u305f\u3081\u3001\u3053\u306e\u8a08\u7b97\u306f\u30aa\u30fc\u30d0\u30fc\u30d5\u30ed\u30fc\u3059\u308b\u3053\u3068\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n
if (sk->sk_type == SOCK_DGRAM) {\r\n\u2026\r\nelse {\r\n    unsigned int maclen = skb_network_offset(skb);\r\n    netoff = TPACKET_ALIGN(po->tp_hdrlen +\r\n                          (maclen < 16 ? 16 : maclen)) + po->tp_reserve;\r\n    if (po->has_vnet_hdr) {\r\n        netoff += sizeof(struct virtio_net_hdr);\r\n        do_vnet = true;\r\n    }\r\n    macoff = netoff \u2013 maclen;\r\n}<\/pre>\n
\u56f37. tpacket_rcv<\/span>\u5185\u306e\u6f14\u7b97<\/em><\/span><\/p>\n
\u56f37\u306b\u793a\u3059\u3088\u3046\u306b\u3001\u30bd\u30b1\u30c3\u30c8\u3067PACKET_VNET_HDR<\/span>\u30aa\u30d7\u30b7\u30e7\u30f3\u304c\u8a2d\u5b9a\u3055\u308c\u3066\u3044\u308c\u3070\u3001Ethernet\u30d8\u30c3\u30c0\u30fc\u306e\u3059\u3050\u5f8c\u308d\u306b\u4f4d\u7f6e\u3059\u308bvirtio_net_hdr<\/span>\u69cb\u9020\u4f53\u306b\u5bfe\u5fdc\u3059\u308b\u305f\u3081\u306b\u3001sizeof(struct virtio_net_hdr)<\/span>\u304c\u30bd\u30b1\u30c3\u30c8\u306b\u8ffd\u52a0\u3055\u308c\u307e\u3059\u3002\u6700\u5f8c\u306b\u3001Ethernet\u30d8\u30c3\u30c0\u30fc\u306e\u30aa\u30d5\u30bb\u30c3\u30c8\u304c\u8a08\u7b97\u3055\u308c\u3001macoff<\/span>\u306b\u4fdd\u5b58\u3055\u308c\u307e\u3059\u3002<\/p>\n
\u4ee5\u4e0b\u306e\u56f38\u306b\u793a\u3059\u3088\u3046\u306b\u3001\u3053\u306e\u95a2\u6570\u3067\u306f\u3053\u306e\u5f8c\u3001virtio_net_hdr_from_skb<\/span>\u95a2\u6570\u3092\u4f7f\u7528\u3057\u3066\u3001virtio_net_hdr<\/span>\u69cb\u9020\u4f53\u304c\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u306b\u66f8\u304d\u8fbc\u307e\u308c\u307e\u3059\u3002\u56f38\u3067\u306f\u3001h.raw<\/span>\u306f\u3001(alloc_pg_vec<\/span>\u3067\u5272\u308a\u5f53\u3066\u3089\u308c\u305f)\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u3067\u73fe\u5728\u7a7a\u3044\u3066\u3044\u308b\u30d5\u30ec\u30fc\u30e0\u3092\u30dd\u30a4\u30f3\u30c8\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n
if (do_vnet &&\r\n    virtio_net_hdr_from_skb(skb, h.raw + macoff \u2013\r\n                            sizeof(struct virtio_net_hdr),\r\n                            vio_le(), true, 0))\r\n    goto drop_n_account;<\/pre>\n
\u56f38.tpacket_rcv<\/span>\u5185\u306evirtio_net_hdr_from_skb<\/span>\u95a2\u6570\u3078\u306e\u547c\u3073\u51fa\u3057<\/em><\/span><\/p>\n
\u6700\u521d\u306f\u3001macoff<\/span>\u304c\u30d6\u30ed\u30c3\u30af\u306e\u30b5\u30a4\u30ba\u3088\u308a\u5927\u304d\u3044\u5024\u3092\u53d7\u3051\u53d6\u308c(\u30a2\u30f3\u30c0\u30fc\u30d5\u30ed\u30fc\u304b\u3089)\u3001\u30d0\u30c3\u30d5\u30a1\u306e\u5883\u754c\u3092\u8d8a\u3048\u3066\u66f8\u304d\u8fbc\u3081\u308b\u3088\u3046\u306b\u3001\u30aa\u30fc\u30d0\u30fc\u30d5\u30ed\u30fc\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u306b\u3088\u308anetoff<\/span>\u3092\u5c0f\u3055\u3044\u5024\u306b\u3067\u304d\u308b\u306e\u3067\u306f\u306a\u3044\u304b\u3068\u8003\u3048\u307e\u3057\u305f\u3002
\n\u3057\u304b\u3057\u3001\u3053\u308c\u306f\u4ee5\u4e0b\u306e\u30c1\u30a7\u30c3\u30af\u306b\u3088\u308a\u963b\u307e\u308c\u307e\u3059\u3002<\/p>\n
if (po->tp_version <= TPACKET_V2) { if (macoff + snaplen > po->rx_ring.frame_size) {\r\n    \u2026\r\n    \u2026\r\n        snaplen = po->rx_ring.frame_size \u2013 macoff;\r\n        if ((int)snaplen < 0) {\r\n            snaplen = 0;\r\n            do_vnet = false;\r\n        }\r\n}<\/pre>\n
\u56f39.tpacket_rcv<\/span>\u95a2\u6570\u5185\u306e\u5225\u306e\u6f14\u7b97\u30c1\u30a7\u30c3\u30af<\/em><\/span><\/p>\n
netoff<\/span>\u3092\u30aa\u30fc\u30d0\u30fc\u30d5\u30ed\u30fc\u3055\u305b\u308b\u3053\u3068\u306b\u3088\u308a\u307e\u3060macoff<\/span>\u3092\u3088\u308a\u5c0f\u3055\u3044\u6574\u6570\u5024\u306b\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u308b\u305f\u3081\u3001\u3053\u306e\u30c1\u30a7\u30c3\u30af\u3067\u306f\u5341\u5206\u306b\u30e1\u30e2\u30ea\u7834\u640d\u3092\u9632\u3050\u3053\u3068\u304c\u3067\u304d\u307e\u305b\u3093\u3002\u5177\u4f53\u7684\u306b\u306f\u3001macoff<\/span>\u3092\u300110\u30d0\u30a4\u30c8\u3067\u3042\u308bsizeof(struct virtio_net_hdr)<\/span>\u3088\u308a\u5c0f\u3055\u304f\u3057\u3001virtio_net_hdr_from_skb<\/span>\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u306b\u3088\u308a\u3001\u30d0\u30c3\u30d5\u30a1\u306e\u5883\u754c\u306e\u5f8c\u308d\u306b\u66f8\u304d\u8fbc\u3080\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
\u30d7\u30ea\u30df\u30c6\u30a3\u30d6<\/strong><\/h4>\n
macoff<\/span>\u306e\u5024\u3092\u5236\u5fa1\u3059\u308b\u3053\u3068\u306b\u3088\u308a\u3001\u6700\u5927\u3067\u30ea\u30f3\u30b0\u30d0\u30c3\u30d5\u30a1\u306e10\u30d0\u30a4\u30c8\u5f8c\u308d\u307e\u3067\u3001\u5236\u5fa1\u3055\u308c\u305f\u30aa\u30d5\u30bb\u30c3\u30c8\u5185\u306evirtio_net_hdr<\/span>\u69cb\u9020\u4f53\u3092\u521d\u671f\u5316\u3067\u304d\u307e\u3059\u3002virtio_net_hdr_from_skb<\/span>\u95a2\u6570\u3067\u306f\u3001\u307e\u305a\u69cb\u9020\u4f53\u5168\u4f53\u3092\u30bc\u30ed\u306b\u3057\u3066\u304b\u3089\u3001skb<\/span>\u69cb\u9020\u4f53\u306b\u57fa\u3065\u3044\u3066\u3001\u69cb\u9020\u4f53\u5185\u306e\u3044\u304f\u3064\u304b\u306e\u30d5\u30a3\u30fc\u30eb\u30c9\u3092\u521d\u671f\u5316\u3057\u307e\u3059\u3002<\/p>\n
static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,\r\n                                          struct virtio_net_hdr *hdr,\r\n                                          bool little_endian,\r\n                                          bool has_data_valid,\r\n                                          int vlan_hlen)\r\n{\r\n    memset(hdr, 0, sizeof(*hdr)); \/* no info leak *\/\r\n    if (skb_is_gso(skb)) {\r\n    \u2026\r\n    if (skb->ip_summed == CHECKSUM_PARTIAL) {\r\n    \u2026<\/pre>\n
\u56f310.virtio_net_hdr_from_skb<\/span>\u95a2\u6570\u306e\u5b9f\u88c5<\/em><\/span><\/p>\n
\u305f\u3060\u3057\u3001\u69cb\u9020\u4f53\u306b\u30bc\u30ed\u3060\u3051\u304c\u66f8\u304d\u8fbc\u307e\u308c\u308b\u3088\u3046\u306bskb<\/span>\u3092\u8a2d\u5b9a\u3067\u304d\u307e\u3059\u3002\u3053\u308c\u306b\u3088\u308a\u3001__get_free_pages<\/span>\u5272\u308a\u5f53\u3066\u306e\u5f8c\u308d\u306e1\uff5e10\u30d0\u30a4\u30c8\u3092\u30bc\u30ed\u306b\u3059\u308b\u3053\u3068\u304c\u53ef\u80fd\u306b\u306a\u308a\u307e\u3059\u3002\u30d2\u30fc\u30d7\u64cd\u4f5c\u3092\u4f55\u3082\u884c\u308f\u306a\u304f\u3066\u3082\u3001\u30ab\u30fc\u30cd\u30eb\u30af\u30e9\u30c3\u30b7\u30e5\u304c\u305f\u3060\u3061\u306b\u767a\u751f\u3057\u307e\u3059\u3002<\/p>\n
PoC<\/strong><\/h4>\n
\u3053\u306e\u8106\u5f31\u6027\u3092\u30c8\u30ea\u30ac\u30fc\u3059\u308b\u305f\u3081\u306ePoC\u30b3\u30fc\u30c9\u306b\u3064\u3044\u3066\u306f\u3001\u3053\u3061\u3089\u306eOpenwall\u306e\u30b9\u30ec\u30c3\u30c9<\/a>\u3092\u53c2\u7167\u3057\u3066\u304f\u3060\u3055\u3044\u3002<\/p>\n
\u30d1\u30c3\u30c1<\/strong><\/h4>\n
\u3053\u306e\u4e0d\u5177\u5408\u3092\u4fee\u6b63\u3059\u308b\u305f\u3081\u306b\u3001\u4ee5\u4e0b\u306e\u30d1\u30c3\u30c1<\/a>\u3092\u63d0\u6848\u3057\u307e\u3057\u305f\u3002<\/p>\n
\"The
\u56f311.\u4e0d\u5177\u5408\u306b\u5bfe\u3057\u3066\u63d0\u6848\u3057\u305f\u30d1\u30c3\u30c1<\/figcaption><\/figure>\n
\u8003\u3048\u65b9\u3068\u3057\u3066\u306f\u3001netoff<\/span>\u306e\u578b\u3092unsigned short<\/span>\u304b\u3089unsigned int<\/span>\u306b\u5909\u66f4\u3059\u308c\u3070\u3001USHRT_MAX<\/span>\u3092\u8d85\u3048\u308b\u304b\u3069\u3046\u304b\u3092\u30c1\u30a7\u30c3\u30af\u3067\u304d\u308b\u306e\u3067\u3001\u8d85\u3048\u305f\u5834\u5408\u306f\u30d1\u30b1\u30c3\u30c8\u3092\u30c9\u30ed\u30c3\u30d7\u3057\u3001\u305d\u308c\u4ee5\u4e0a\u306e\u51e6\u7406\u3092\u9632\u6b62\u3067\u304d\u308b\u3068\u3044\u3046\u3082\u306e\u3067\u3059\u3002<\/p>\n
\u30a8\u30af\u30b9\u30d7\u30ed\u30a4\u30c8\u65b9\u6cd5\u306b\u3064\u3044\u3066<\/h2>\n
\u3053\u306e\u8106\u5f31\u6027\u3092\u60aa\u7528\u3059\u308b\u65b9\u6cd5\u3068\u3057\u3066\u3001\u30d7\u30ea\u30df\u30c6\u30a3\u30d6\u3092use-after-free(\u89e3\u653e\u6e08\u307f\u30e1\u30e2\u30ea\u4f7f\u7528)\u306b\u5909\u63db\u3059\u308b\u3053\u3068\u304c\u8003\u3048\u3089\u308c\u307e\u3059\u3002\u3053\u306e\u305f\u3081\u306b\u3001\u3044\u305a\u308c\u304b\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u53c2\u7167\u30ab\u30a6\u30f3\u30c8\u3092\u30c7\u30af\u30ea\u30e1\u30f3\u30c8\u3057\u307e\u3059\u3002\u305f\u3068\u3048\u3070\u3001\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306erefcount\u5024\u304c0x10001\u306e\u5834\u5408\u3001\u7834\u640d\u5f8c\u306f\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u306a\u308a\u307e\u3059\u3002<\/p>\n
\"This
\u56f312.\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306erefcount\u5185\u306e\u30d0\u30a4\u30c8\u3092\u30bc\u30ed\u306b\u3059\u308b<\/figcaption><\/figure>\n
\u4ee5\u4e0b\u306e\u56f313\u306b\u793a\u3059\u3088\u3046\u306b\u3001\u7834\u640d\u5f8c\u306erefcount\u5024\u306f0x1\u306b\u306a\u308b\u306e\u3067\u30011\u3064\u53c2\u7167\u3092release\u3059\u308b\u3068\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u304c\u89e3\u653e\u3055\u308c\u307e\u3059\u3002<\/p>\n
\u305f\u3060\u3057\u3001\u3053\u308c\u304c\u884c\u308f\u308c\u308b\u305f\u3081\u306b\u306f\u3001\u4ee5\u4e0b\u306e\u5236\u7d04\u304c\u6e80\u305f\u3055\u308c\u308b\u5fc5\u8981\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n