Code: int cipso_v4_req_setattr(struct request_sock *req,
			 const struct cipso_v4_doi *doi_def,
			 const struct netlbl_lsm_secattr *secattr)
{
	int ret_val = -EPERM;
 	unsigned char *buf = NULL;
 	u32 buf_len;
 	u32 opt_len;
	struct ip_options *opt = NULL;
 	struct inet_request_sock *req_inet;
 
 	/* We allocate the maximum CIPSO option size here so we are probably
	 * being a little wasteful, but it makes our life _much_ easier later
	 * on and after all we are only talking about 40 bytes. */
	buf_len = CIPSO_V4_OPT_LEN_MAX;
	buf = kmalloc(buf_len, GFP_ATOMIC);
	if (buf == NULL) {
		ret_val = -ENOMEM;
		goto req_setattr_failure;
	}

	ret_val = cipso_v4_genopt(buf, buf_len, doi_def, secattr);
	if (ret_val < 0)
		goto req_setattr_failure;
	buf_len = ret_val;

	/* We can't use ip_options_get() directly because it makes a call to
	 * ip_options_get_alloc() which allocates memory with GFP_KERNEL and
	 * we won't always have CAP_NET_RAW even though we _always_ want to
	 * set the IPOPT_CIPSO option. */
	opt_len = (buf_len + 3) & ~3;
	opt = kzalloc(sizeof(*opt) + opt_len, GFP_ATOMIC);
	if (opt == NULL) {
 		ret_val = -ENOMEM;
 		goto req_setattr_failure;
 	}
	memcpy(opt->__data, buf, buf_len);
	opt->optlen = opt_len;
	opt->cipso = sizeof(struct iphdr);
 	kfree(buf);
 	buf = NULL;
 
 	req_inet = inet_rsk(req);
 	opt = xchg(&req_inet->opt, opt);
	kfree(opt);
 
 	return 0;
 
req_setattr_failure:
	kfree(buf);
	kfree(opt);
	return ret_val;
}

Vulnerability Type: DoS 
CWE ID: CWE-362
Summary: Race condition in the IP implementation in the Linux kernel before 3.0 might allow remote attackers to cause a denial of service (slab corruption and system crash) by sending packets to an application that sets socket options during the handling of network traffic.
Commit Message: inet: add RCU protection to inet->opt

We lack proper synchronization to manipulate inet->opt ip_options

Problem is ip_make_skb() calls ip_setup_cork() and
ip_setup_cork() possibly makes a copy of ipc->opt (struct ip_options),
without any protection against another thread manipulating inet->opt.

Another thread can change inet->opt pointer and free old one under us.

Use RCU to protect inet->opt (changed to inet->inet_opt).

Instead of handling atomic refcounts, just copy ip_options when
necessary, to avoid cache line dirtying.

We cant insert an rcu_head in struct ip_options since its included in
skb->cb[], so this patch is large because I had to introduce a new
ip_options_rcu structure.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>