Re: Weird modem behaviour in 2.5.73-mm1

[Stephen Hemminger <shemminger@xxxxxxxx>]

Try this patch, it is more paranoid in some of the code paths.
I did get PPP over a null modem cable working between 2.4.18 and 2.5.73 with 
the PPP patches.

diff -Nru a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
--- a/drivers/net/ppp_generic.c Wed Jun 25 17:32:29 2003
+++ b/drivers/net/ppp_generic.c Wed Jun 25 17:32:29 2003
@@ -1448,7 +1448,7 @@
                if (ppp->vj == 0 || (ppp->flags & SC_REJ_COMP_TCP))
                        goto err;
 
-               if (skb_tailroom(skb) < 124 || skb_is_nonlinear(skb) ) {
+               if (skb_tailroom(skb) < 124) {
                        /* copy to a new sk_buff with more tailroom */
                        ns = dev_alloc_skb(skb->len + 128);
                        if (ns == 0) {
@@ -1459,7 +1459,9 @@
                        memcpy(skb_put(ns, skb->len), skb->data, skb->len);
                        kfree_skb(skb);
                        skb = ns;
-               }
+               } else if (!pskb_may_pull(skb, skb->len)) 
+                       goto err;
+
                len = slhc_uncompress(ppp->vj, skb->data + 2, skb->len - 2);
                if (len <= 0) {
                        printk(KERN_DEBUG "PPP: VJ decompression error\n");
@@ -2033,11 +2035,15 @@
 static void
 ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound)
 {
-       unsigned char *dp = skb->data + 2;
+       unsigned char *dp;
        int len;
 
-       if (!pskb_may_pull(skb, CCP_HDRLEN + 2)
-           || skb->len < (len = CCP_LENGTH(dp)) + 2)
+       if (!pskb_may_pull(skb, CCP_HDRLEN + 2))
+               return;
+
+       dp = skb->data + 2;
+       len = CCP_LENGTH(dp);
+       if (skb->len < len +2)
                return;         /* too short */
 
        switch (CCP_CODE(dp)) {