[PPP] generic: Fix receive path data clobbering & non-linear handling

This patch adds missing pskb_may_pull calls to deal with non-linear
packets that may arrive from pppoe or pppol2tp.

It also copies cloned packets before writing over them.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 19 deletions

diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
index 7e21342becb..4b49d0e8c7e 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -1525,7 +1525,7 @@ ppp_input_error(struct ppp_channel *chan, int code)
 static void
 ppp_receive_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
 {
-        if (skb->len >= 2) {
+        if (pskb_may_pull(skb, 2)) {
 #ifdef CONFIG_PPP_MULTILINK
                 /* XXX do channel-level decompression here */
                 if (PPP_PROTO(skb) == PPP_MP)
@@ -1577,7 +1577,7 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)
                 if (ppp->vj == 0 || (ppp->flags & SC_REJ_COMP_TCP))
                         goto err;
 
-                if (skb_tailroom(skb) < 124) {
+                if (skb_tailroom(skb) < 124 || skb_cloned(skb)) {
                         /* copy to a new sk_buff with more tailroom */
                         ns = dev_alloc_skb(skb->len + 128);
                         if (ns == 0) {
@@ -1648,23 +1648,29 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)
                 /* check if the packet passes the pass and active filters */
                 /* the filter instructions are constructed assuming
                    a four-byte PPP header on each packet */
-                *skb_push(skb, 2) = 0;
-                if (ppp->pass_filter
-                    && sk_run_filter(skb, ppp->pass_filter,
-                                     ppp->pass_len) == 0) {
-                        if (ppp->debug & 1)
-                                printk(KERN_DEBUG "PPP: inbound frame not passed\n");
-                        kfree_skb(skb);
-                        return;
-                }
-                if (!(ppp->active_filter
-                      && sk_run_filter(skb, ppp->active_filter,
-                                       ppp->active_len) == 0))
-                        ppp->last_recv = jiffies;
-                skb_pull(skb, 2);
-#else
-                ppp->last_recv = jiffies;
+                if (ppp->pass_filter || ppp->active_filter) {
+                        if (skb_cloned(skb) &&
+                            pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+                                goto err;
+
+                        *skb_push(skb, 2) = 0;
+                        if (ppp->pass_filter
+                            && sk_run_filter(skb, ppp->pass_filter,
+                                             ppp->pass_len) == 0) {
+                                if (ppp->debug & 1)
+                                        printk(KERN_DEBUG "PPP: inbound frame "
+                                               "not passed\n");
+                                kfree_skb(skb);
+                                return;
+                        }
+                        if (!(ppp->active_filter
+                              && sk_run_filter(skb, ppp->active_filter,
+                                               ppp->active_len) == 0))
+                                ppp->last_recv = jiffies;
+                        __skb_pull(skb, 2);
+                } else
 #endif /* CONFIG_PPP_FILTER */
+                        ppp->last_recv = jiffies;
 
                 if ((ppp->dev->flags & IFF_UP) == 0
                     || ppp->npmode[npi] != NPMODE_PASS) {
@@ -1762,7 +1768,7 @@ ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
         struct channel *ch;
         int mphdrlen = (ppp->flags & SC_MP_SHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;
 
-        if (!pskb_may_pull(skb, mphdrlen) || ppp->mrru == 0)
+        if (!pskb_may_pull(skb, mphdrlen + 1) || ppp->mrru == 0)
                 goto err;               /* no good, throw it away */
 
         /* Decode sequence number and begin/end bits */