cls_u32: use skb_header_pointer() to dereference data safely

use skb_header_pointer() to dereference data safely

the original skb->data dereference isn't safe, as there isn't any skb->len or
skb_is_nonlinear() check. skb_header_pointer() is used instead in this patch.
And when the skb isn't long enough, we terminate the function u32_classify()
immediately with -1.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 36 insertions, 13 deletions

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 96275422c619..4f522143811e 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -98,11 +98,11 @@ static int u32_classify(struct sk_buff *skb, struct tcf_proto *tp, struct tcf_re
 {
         struct {
                 struct tc_u_knode *knode;
-                u8                *ptr;
+                unsigned int      off;
         } stack[TC_U32_MAXDEPTH];
 
         struct tc_u_hnode *ht = (struct tc_u_hnode*)tp->root;
-        u8 *ptr = skb_network_header(skb);
+        unsigned int off = skb_network_offset(skb);
         struct tc_u_knode *n;
         int sdepth = 0;
         int off2 = 0;
@@ -134,8 +134,14 @@ next_knode:
 #endif
 
                 for (i = n->sel.nkeys; i>0; i--, key++) {
-
-                        if ((*(__be32*)(ptr+key->off+(off2&key->offmask))^key->val)&key->mask) {
+                        unsigned int toff;
+                        __be32 *data, _data;
+
+                        toff = off + key->off + (off2 & key->offmask);
+                        data = skb_header_pointer(skb, toff, 4, &_data);
+                        if (!data)
+                                goto out;
+                        if ((*data ^ key->val) & key->mask) {
                                 n = n->next;
                                 goto next_knode;
                         }
@@ -174,29 +180,45 @@ check_terminal:
                 if (sdepth >= TC_U32_MAXDEPTH)
                         goto deadloop;
                 stack[sdepth].knode = n;
-                stack[sdepth].ptr = ptr;
+                stack[sdepth].off = off;
                 sdepth++;
 
                 ht = n->ht_down;
                 sel = 0;
-                if (ht->divisor)
-                        sel = ht->divisor&u32_hash_fold(*(__be32*)(ptr+n->sel.hoff), &n->sel,n->fshift);
-
+                if (ht->divisor) {
+                        __be32 *data, _data;
+
+                        data = skb_header_pointer(skb, off + n->sel.hoff, 4,
+                                                  &_data);
+                        if (!data)
+                                goto out;
+                        sel = ht->divisor & u32_hash_fold(*data, &n->sel,
+                                                          n->fshift);
+                }
                 if (!(n->sel.flags&(TC_U32_VAROFFSET|TC_U32_OFFSET|TC_U32_EAT)))
                         goto next_ht;
 
                 if (n->sel.flags&(TC_U32_OFFSET|TC_U32_VAROFFSET)) {
                         off2 = n->sel.off + 3;
-                        if (n->sel.flags&TC_U32_VAROFFSET)
-                                off2 += ntohs(n->sel.offmask & *(__be16*)(ptr+n->sel.offoff)) >>n->sel.offshift;
+                        if (n->sel.flags & TC_U32_VAROFFSET) {
+                                __be16 *data, _data;
+
+                                data = skb_header_pointer(skb,
+                                                          off + n->sel.offoff,
+                                                          2, &_data);
+                                if (!data)
+                                        goto out;
+                                off2 += ntohs(n->sel.offmask & *data) >>
+                                        n->sel.offshift;
+                        }
                         off2 &= ~3;
                 }
                 if (n->sel.flags&TC_U32_EAT) {
-                        ptr += off2;
+                        off += off2;
                         off2 = 0;
                 }
 
-                if (ptr < skb_tail_pointer(skb))
+                if (off < skb->len)
                         goto next_ht;
         }
 
@@ -204,9 +226,10 @@ check_terminal:
         if (sdepth--) {
                 n = stack[sdepth].knode;
                 ht = n->ht_up;
-                ptr = stack[sdepth].ptr;
+                off = stack[sdepth].off;
                 goto check_terminal;
         }
+out:
         return -1;
 
 deadloop: