bad usage of the shutdown system call produce a packet with null ip addresses

[david guéluy]

Hi,

By using a PFIL_HOOK on FreeBSD 7.1-prerelease, I notice that I  
receive some packets from 0.0.0.0 to 0.0.0.0.

A buggy program in userland produce these packets when the shutdown  
system call is used on
a socket which is not connected.

Even if it's a bad usage of a system call, this case can produce  
strange behaviours, I think
it's necessary to add some checks in tcp_usr_shutdown.

Here is a short sample to reproduce that case :

test.c

#include <sys/socket.h>
#include <stdio.h>

int main(void)
{
	int			fd;

	fd = socket(AF_INET, SOCK_STREAM, 0);
	if (fd == -1)
		return 1;
	shutdown(fd, SHUT_RDWR);
	close(fd);
         return 0;
}

Add some debug in the kernel

[usr/src/sys/netinet]# diff -C4 ip_output.c.origin ip_output.c
*** ip_output.c.origin  Mon Feb 23 10:27:52 2009
--- ip_output.c Fri Feb 20 15:23:39 2009
***************
*** 135,142 ****
--- 135,151 ----
                        hlen = len;
        }
        ip = mtod(m, struct ip *);

+ #define PRINTIP(a)      printf("%u.%u.%u.%u",  
(unsigned)ntohl(a)>>24&0xFF, (unsigned)ntohl(a)>>16&0xFF,  
(unsigned)ntohl(a)>>8&0xFF, (unsigned)ntohl(a)&0xFF)
+
+               if (m->m_pkthdr.rcvif != NULL)
+                       printf(" if %s ", m->m_pkthdr.rcvif->if_xname);
+               printf(" proto %d src ", (int)ip->ip_p); PRINTIP(ip- 
 >ip_src.s_addr);
+               printf(" dst "); PRINTIP(ip->ip_dst.s_addr);
+               printf(" ttl %u\n", (unsigned)ip->ip_ttl);
+
+

./test
proto 6 src 0.0.0.0 dst 0.0.0.0 ttl 64

Best regards,
Guéluy David