[SCTP]: Prevent possible infinite recursion with multiple bundled DATA. (672e7cca) · Commits · 戴 / test

There is a rare situation that causes lksctp to go into infinite recursion and crash the system. The trigger is a packet that contains at least the first two DATA fragments of a message bundled together. The recursion is triggered when the user data buffer is smaller that the full data message. The problem is that we clone the skb for every fragment in the message. When reassembling the full message, we try to link skbs from the "first fragment" clone using the frag_list. However, since the frag_list is shared between two clones in this rare situation, we end up setting the frag_list pointer of the second fragment to point to itself. This causes sctp_skb_pull() to potentially recurse indefinitely. Proposed solution is to make a copy of the skb when attempting to link things using frag_list. Signed-off-by:

Vladislav Yasevich <vladsilav.yasevich@hp.com> Signed-off-by:

Sridhar Samudrala <sri@us.ibm.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/sctp/ulpqueue.c

+25 −2

Original line number	Diff line number	Diff line
		@@ -279,6 +279,7 @@ static inline void sctp_ulpq_store_reasm(struct sctp_ulpq *ulpq,
		static struct sctp_ulpevent sctp_make_reassembled_event(struct sk_buff_head queue, struct sk_buff f_frag, struct sk_buff l_frag)
		{
		struct sk_buff *pos;
		struct sk_buff *new = NULL;
		struct sctp_ulpevent *event;
		struct sk_buff pnext, last;
		struct sk_buff *list = skb_shinfo(f_frag)->frag_list;
		@@ -297,11 +298,33 @@ static struct sctp_ulpevent sctp_make_reassembled_event(struct sk_buff_head qu
		*/
		if (last)
		last->next = pos;
		else
		else {
		if (skb_cloned(f_frag)) {
		/* This is a cloned skb, we can't just modify
		* the frag_list. We need a new skb to do that.
		* Instead of calling skb_unshare(), we'll do it
		* ourselves since we need to delay the free.
		*/
		new = skb_copy(f_frag, GFP_ATOMIC);
		if (!new)
		return NULL; /* try again later */

		new->sk = f_frag->sk;

		skb_shinfo(new)->frag_list = pos;
		} else
		skb_shinfo(f_frag)->frag_list = pos;
		}

		/* Remove the first fragment from the reassembly queue. */
		__skb_unlink(f_frag, queue);

		/* if we did unshare, then free the old skb and re-assign */
		if (new) {
		kfree_skb(f_frag);
		f_frag = new;
		}

		while (pos) {

		pnext = pos->next;

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