Messages in this thread | | | From | Jacob Siverskog <> | Date | Wed, 30 Dec 2015 12:14:42 +0100 | Subject | Re: [PATCH] net: Fix potential NULL pointer dereference in __skb_try_recv_datagram |
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On Tue, Dec 29, 2015 at 9:08 PM, David Miller <davem@davemloft.net> wrote: > From: Rainer Weikusat <rweikusat@mobileactivedefense.com> > Date: Tue, 29 Dec 2015 19:42:36 +0000 > >> Jacob Siverskog <jacob@teenage.engineering> writes: >>> This should fix a NULL pointer dereference I encountered (dump >>> below). Since __skb_unlink is called while walking, >>> skb_queue_walk_safe should be used. >> >> The code in question is: > ... >> __skb_unlink is only called prior to returning from the function. >> Consequently, it won't affect the skb_queue_walk code. > > Agreed, this patch doesn't fix anything.
Ok. Thanks for your feedback. How do you believe the issue could be solved? Investigating it gives:
static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list) { struct sk_buff *next, *prev;
list->qlen--; 51c: e2433001 sub r3, r3, #1 520: e58b3074 str r3, [fp, #116] ; 0x74 next = skb->next; prev = skb->prev; 524: e894000c ldm r4, {r2, r3} skb->next = skb->prev = NULL; 528: e5841000 str r1, [r4] 52c: e5841004 str r1, [r4, #4] next->prev = prev; 530: e5823004 str r3, [r2, #4] <-- trapping instruction (r2 NULL)
Register contents: r7 : c58cfe1c r6 : c06351d0 r5 : c77810ac r4 : c583eac0 r3 : 00000000 r2 : 00000000 r1 : 00000000 r0 : 20000013
If I understand this correctly, then r4 = skb, r2 = next, r3 = prev.
Should there be a check for this in __skb_try_recv_datagram?
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