Commit 9dde0cd3 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by David S. Miller
Browse files

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 eedade12 ("net: kfree_skb_list use
kmem_cache_free_bulk"). For completeness mentioned bug have been fixed in
commit f72ff8b8 ("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: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 149e8fb0

include/linux/poison.h

+3 −0
Original line number Diff line number Diff line
@@ -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))

include/linux/skbuff.h

+7 −0
Original line number Diff line number Diff line
@@ -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);  \

net/core/skbuff.c

+3 −1
Original line number Diff line number Diff line
@@ -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;

	}