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Subject[PATCH v3] sctp: fix refcount bug in sctp_wfree
Date
Do accounting for skb's real sk.
In some case skb->sk != asoc->base.sk:

for the trouble SKB, it was in outq->transmitted queue

sctp_outq_sack
sctp_check_transmitted
SKB was moved to outq->sack
then throw away the sack queue
SKB was deleted from outq->sack
(but the datamsg held SKB at sctp_datamsg_to_asoc
So, sctp_wfree was not called to destroy SKB)

then migrate happened

sctp_for_each_tx_datachunk(
sctp_clear_owner_w);
sctp_assoc_migrate();
sctp_for_each_tx_datachunk(
sctp_set_owner_w);
SKB was not in the outq, and was not changed to newsk

finally

__sctp_outq_teardown
sctp_chunk_put (for another skb)
sctp_datamsg_put
__kfree_skb(msg->frag_list)
sctp_wfree (for SKB)
this case in sctp_wfree SKB->sk was oldsk.

It looks only trouble here so handling it in sctp_wfree is enough.

Reported-and-tested-by: syzbot+cea71eec5d6de256d54d@syzkaller.appspotmail.com
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
---
net/sctp/socket.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 1b56fc440606..5f5c28b30e25 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -9080,7 +9080,7 @@ static void sctp_wfree(struct sk_buff *skb)
{
struct sctp_chunk *chunk = skb_shinfo(skb)->destructor_arg;
struct sctp_association *asoc = chunk->asoc;
- struct sock *sk = asoc->base.sk;
+ struct sock *sk = skb->sk;

sk_mem_uncharge(sk, skb->truesize);
sk->sk_wmem_queued -= skb->truesize + sizeof(struct sctp_chunk);
@@ -9109,7 +9109,7 @@ static void sctp_wfree(struct sk_buff *skb)
}

sock_wfree(skb);
- sctp_wake_up_waiters(sk, asoc);
+ sctp_wake_up_waiters(asoc->base.sk, asoc);

sctp_association_put(asoc);
}
--
2.17.1
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