[PATCH] Socket filter instruction limit validation

["Kris Katterjohn" <kjak@ispwest.com>]

This patch checks to make sure that the number of instructions doesn't surpass
BPF_MAXINSNS in sk_chk_filter().

Signed-off-by: Kris Katterjohn <kjak@users.sourceforge.net>

---

This is a diff from 2.6.15-rc5. And I am not subscribed, so please CC me on any
replies.

The previous check in sk_chk_filter() doesn't seem very logical to me because it
should either be limited to BPF_MAXINSNS or only limited by the max value of an
`int' (not really limited). sk_attach_filter() and get_filter() in
drivers/net/ppp_generic.c limit it to BPF_MAXINSNS, but get_filter() in
drivers/isdn/i4l/isdn_ppp.c and anything else that will use it only get this
seemingly "random" limit.

This way it is checked for in only one place, and has a single constant limit.

Thanks!

--- x/net/core/filter.c	2005-12-06 04:01:50.000000000 -0600
+++ y/net/core/filter.c	2005-12-06 04:04:23.000000000 -0600
@@ -293,7 +293,8 @@ int sk_chk_filter(struct sock_filter *fi
 	struct sock_filter *ftest;
 	int pc;
 
-	if (((unsigned int)flen >= (~0U / sizeof(struct sock_filter))) || flen == 0)
+	/* check for valid number of instructions -Kris Katterjohn 2005-12-06 */
+	if (flen == 0 || flen > BPF_MAXINSNS)
 		return -EINVAL;
 
 	/* check the filter code now */
@@ -359,9 +360,9 @@ int sk_attach_filter(struct sock_fprog *
 	unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
 	int err;
 
-	/* Make sure new filter is there and in the right amounts. */
-        if (fprog->filter == NULL || fprog->len > BPF_MAXINSNS)
-                return -EINVAL;
+	/* Make sure new filter is there */
+	if (fprog->filter == NULL)
+		return -EINVAL;
 
 	fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
 	if (!fp)