BugTraq
(CVE-2013-1059) Linux Kernel libceph Null Pointer Dereference Vulnerability Jul 10 2013 02:21AM
chanam park hkpco kr
Original URL: http://hkpco.kr/advisory/CVE-2013-1059.txt

< Linux Kernel libceph Null Pointer Dereference Vulnerability (CVE-2013-1059) >

Author - Chanam Park (@hkpco)
Website - http://hkpco.kr/
Date - 2013. 07. 06

0. Introduction

This is very brief advisory just to record the vulnerability which I discovered in my spare time.
A remote attacker, malicious ceph monitor, can make an exploit to cause a denial-of-service condition by sending the crafted auth_reply message.
It could possibly lead to another impacts such as remote code execution if some other vulnerabilities are combined.
An explanation is based on linux kernel 3.10 which is latest version now.

1. What's Ceph?

Check these links below.

http://en.wikipedia.org/wiki/Ceph_(storage)
http://ceph.com/

2. Vulnerability

The vulnerability is triggered by a null pointer dereferencing problem which can raise a kernel crash remotely.

Here, I will show you the code flow about vulnerability.

Let's start with the dispatch() function which handles incoming auth message from the ceph monitor.

http://lxr.linux.no/linux+v3.10/net/ceph/mon_client.c
-------
963 static void dispatch(struct ceph_connection *con, struct ceph_msg *msg)
964 {
965 struct ceph_mon_client *monc = con->private;
966 int type = le16_to_cpu(msg->hdr.type);
967
968 if (!monc)
969 return;
970
971 switch (type) {
972 case CEPH_MSG_AUTH_REPLY:
973 handle_auth_reply(monc, msg); *** [1] ***
974 break;
..
-------

As shown in part [1], It calls handle_auth_reply() once ceph client receives the auth reply message from monitor.

See handle_auth_reply() implementation in the same module, then.

-------
886 static void handle_auth_reply(struct ceph_mon_client *monc,
887 struct ceph_msg *msg)
888 {
889 int ret;
890 int was_auth = 0;
891 int had_debugfs_info, init_debugfs = 0;
892
893 mutex_lock(&monc->mutex);
894 had_debugfs_info = have_debugfs_info(monc);
895 was_auth = ceph_auth_is_authenticated(monc->auth);
896 monc->pending_auth = 0;
897 ret = ceph_handle_auth_reply(monc->auth, msg->front.iov_base, *** [2] ***
898 msg->front.iov_len,
899 monc->m_auth->front.iov_base,
900 monc->m_auth->front_max);
..
-------

At in part [2], It calls ceph_handle_auth_reply().

Move to take a look at the function.

http://lxr.linux.no/linux+v3.10/net/ceph/auth.c
-------
174 int ceph_handle_auth_reply(struct ceph_auth_client *ac,
175 void *buf, size_t len,
176 void *reply_buf, size_t reply_len)
177 {
178 void *p = buf;
179 void *end = buf + len;
180 int protocol;
..
239 ret = ac->ops->handle_reply(ac, result, payload, payload_end);
240 if (ret == -EAGAIN) {
241 ret = ceph_build_auth_request(ac, reply_buf, reply_len); *** [3] ***
242 } else if (ret) {
243 pr_err("auth method '%s' error %d\n", ac->ops->name, ret);
244 }
-------

As you can see in the part [3] above, ceph_build_auth_request() contains a vulnerable code to cause the null pointer dereference.

Let's see how the function implements a vulnerable code below.

http://lxr.linux.no/linux+v3.10/net/ceph/auth.c
-------
144 static int ceph_build_auth_request(struct ceph_auth_client *ac,
145 void *msg_buf, size_t msg_len)
146 {
147 struct ceph_mon_request_header *monhdr = msg_buf;
148 void *p = monhdr + 1;
149 void *end = msg_buf + msg_len;
150 int ret;
151
152 monhdr->have_version = 0;
153 monhdr->session_mon = cpu_to_le16(-1);
154 monhdr->session_mon_tid = 0;
155
156 ceph_encode_32(&p, ac->protocol);
157
158 ret = ac->ops->build_request(ac, p + sizeof(u32), end); *** [3] ***
159 if (ret < 0) {
160 pr_err("error %d building auth method %s request\n", ret,
161 ac->ops->name);
162 goto out;
163 }
164 dout(" built request %d bytes\n", ret);
165 ceph_encode_32(&p, ret);
166 ret = p + ret - msg_buf;
167 out:
168 return ret;
169 }
-------

The code above, at part [3], calls a function pointer from ceph_auth_client structure without any value checking whether it's null or something else.

Moreover, you can see in the next part soon, some function pointers in the structure hasn't been defined at all.

Here's the problematic structure prototypes below.

http://lxr.linux.no/linux+v3.9.6/include/linux/ceph/auth.h
-------
..
25 struct ceph_auth_client_ops {
26 const char *name;
27
..
40 /*
41 * build requests and process replies during monitor
42 * handshake. if handle_reply returns -EAGAIN, we build
43 * another request.
44 */
45 int (*build_request)(struct ceph_auth_client *ac, void *buf, void *end); *** [4] ***
..
71 struct ceph_auth_client {
72 u32 protocol; /* CEPH_AUTH_* */
73 void *private; /* for use by protocol implementation */
74 const struct ceph_auth_client_ops *ops; /* null iff protocol==0 */ *** [5] ***
..
-------

At part [4], ceph_auth_client_ops structure has a build_request() as a member variable.

At part [5], ceph_auth_client_ops is defined within ceph_auth_client structure.

If we confirm that the ceph_auth_client_ops structure does not initialize the build_request() function pointer, and that's being used as it is,

the null pointer dereference can easily occur.

Let's see.

http://lxr.linux.no/linux+v3.10/net/ceph/auth_none.c
-------
103 static const struct ceph_auth_client_ops ceph_auth_none_ops = {
104 .name = "none",
105 .reset = reset,
106 .destroy = destroy,
107 .is_authenticated = is_authenticated,
108 .should_authenticate = should_authenticate,
109 .handle_reply = handle_reply,
110 .create_authorizer = ceph_auth_none_create_authorizer,
111 .destroy_authorizer = ceph_auth_none_destroy_authorizer,
112 };
113
114 int ceph_auth_none_init(struct ceph_auth_client *ac)
115 {
116 struct ceph_auth_none_info *xi;
117
118 dout("ceph_auth_none_init %p\n", ac);
119 xi = kzalloc(sizeof(*xi), GFP_NOFS);
120 if (!xi)
121 return -ENOMEM;
122
123 xi->starting = true;
124 xi->built_authorizer = false;
125
126 ac->protocol = CEPH_AUTH_NONE;
127 ac->private = xi;
128 ac->ops = &ceph_auth_none_ops; *** [6] ***
129 return 0;
130 }
-------

As shown in the part [6] above, ceph_auth_none_ops structure is being used as a ceph operation with no build_request definition.

Boom!,

3. Patch

Tyler Hicks made a fix for it.
https://git.kernel.org/cgit/linux/kernel/git/sage/ceph-client.git/commit
/?id=2cb33cac622afde897aa02d3dcd9fbba8bae839e

4. Credit

Chanam Park discovered this bug.
http://seclists.org/oss-sec/2013/q3/61

5. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2013-1059
http://www.cvedetails.com/cve/CVE-2013-1059/
http://www.openwall.com/lists/oss-security/2013/07/09/7
https://bugzilla.redhat.com/show_bug.cgi?id=977356
http://ceph.com/git/?p=ceph-client.git;a=commit;h=2cb33cac622afde897aa02
d3dcd9fbba8bae839e

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