net: introduce skb_poison_list and use in kfree_skb_list

First user of skb_poison_list is in kfree_skb_list_reason, to catch bugs
earlier like introduced in commit eedade12f4cb ("net: kfree_skb_list use
kmem_cache_free_bulk"). For completeness mentioned bug have been fixed in
commit f72ff8b81ebc ("net: fix kfree_skb_list use of skb_mark_not_on_list").

In case of a bug like mentioned commit we would have seen OOPS with:
 general protection fault, probably for non-canonical address 0xdead000000000870
And content of one the registers e.g. R13: dead000000000800

In this case skb->len is at offset 112 bytes (0x70) why fault happens at
 0x800+0x70 = 0x870

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/poison.h b/include/linux/poison.h
index 2d3249e..2823f90 100644 (file)
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -81,6 +81,9 @@
 /********** net/core/page_pool.c **********/
 #define PP_SIGNATURE           (0x40 + POISON_POINTER_DELTA)
 
+/********** net/core/skbuff.c **********/
+#define SKB_LIST_POISON_NEXT   ((void *)(0x800 + POISON_POINTER_DELTA))
+
 /********** kernel/bpf/ **********/
 #define BPF_PTR_POISON ((void *)(0xeB9FUL + POISON_POINTER_DELTA))
 

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 5ba1218..1fa95b9 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1738,6 +1738,13 @@ static inline void skb_mark_not_on_list(struct sk_buff *skb)
        skb->next = NULL;
 }
 
+static inline void skb_poison_list(struct sk_buff *skb)
+{
+#ifdef CONFIG_DEBUG_NET
+       skb->next = SKB_LIST_POISON_NEXT;
+#endif
+}
+
 /* Iterate through singly-linked GSO fragments of an skb. */
 #define skb_list_walk_safe(first, skb, next_skb)                               \
        for ((skb) = (first), (next_skb) = (skb) ? (skb)->next : NULL; (skb);  \

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 44a1980..624e9e4 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1000,8 +1000,10 @@ kfree_skb_list_reason(struct sk_buff *segs, enum skb_drop_reason reason)
        while (segs) {
                struct sk_buff *next = segs->next;
 
-               if (__kfree_skb_reason(segs, reason))
+               if (__kfree_skb_reason(segs, reason)) {
+                       skb_poison_list(segs);
                        kfree_skb_add_bulk(segs, &sa, reason);
+               }
 
                segs = next;
        }