[PATCH] getsockopt() early argument sanity checking

[Solar Designer]

Willy,

I propose the attached patch (extracted from 2.4.33-ow1) for inclusion
into 2.4.34-pre.

(2.6 kernels could benefit from the same change, too, but at the moment
I am dealing with proper submission of generic changes like this that
are a part of 2.4.33-ow1.)

The patch makes getsockopt(2) sanity-check the value pointed to by
the optlen argument early on.  This is a security hardening measure
intended to prevent exploitation of certain potential vulnerabilities in
socket type specific getsockopt() code on UP systems.

This change has been a part of -ow patches for some years.

Thanks,

-- 
Alexander Peslyak <solar at openwall.com>
GPG key ID: B35D3598  fp: 6429 0D7E F130 C13E C929  6447 73C3 A290 B35D 3598
http://www.openwall.com - bringing security into open computing environments
diff -urpPX nopatch linux-2.4.33/net/socket.c linux/net/socket.c
--- linux-2.4.33/net/socket.c	Wed Jan 19 17:10:14 2005
+++ linux/net/socket.c	Sat Aug 12 08:51:47 2006
@@ -1307,10 +1307,18 @@ asmlinkage long sys_setsockopt(int fd, i
 asmlinkage long sys_getsockopt(int fd, int level, int optname, char *optval, int *optlen)
 {
 	int err;
+	int len;
 	struct socket *sock;
 
 	if ((sock = sockfd_lookup(fd, &err))!=NULL)
 	{
+		/* XXX: insufficient for SMP, but should be redundant anyway */
+		if (get_user(len, optlen))
+			err = -EFAULT;
+		else
+		if (len < 0)
+			err = -EINVAL;
+		else
 		if (level == SOL_SOCKET)
 			err=sock_getsockopt(sock,level,optname,optval,optlen);
 		else