In function sctp_wake_up_waiters(), we need to involve a test
if the association is declared dead. If so, we don't have any
reference to a possible sibling association anymore and need
to invoke sctp_write_space() instead and normally walk the
socket's associations and notify them of new wmem space. The
reason for special casing is that, otherwise, we could run
into the following issue:
sctp_association_free()
`-> list_del(&asoc->asocs) <-- poisons list pointer
asoc->base.dead = true
sctp_outq_free(&asoc->outqueue)
`-> __sctp_outq_teardown()
`-> sctp_chunk_free()
`-> consume_skb()
`-> sctp_wfree()
`-> sctp_wake_up_waiters() <-- dereferences poisoned pointers
if asoc->ep->sndbuf_policy=0
Therefore, only walk the list in an 'optimized' way if we find
that the current association is still active. We could also use
list_del_init() in addition when we call sctp_association_free(),
but as Vlad suggests, we want to trap such bugs and thus leave
it poisoned as is. Stress-testing seems fine now.
Fixes: cd253f9f357d ("net: sctp: wake up all assocs if sndbuf policy is per socket")
Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Cc: Vlad Yasevich <vyasevic@xxxxxxxxxx>
---
v1->v2:
- leave list_del()
net/sctp/socket.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 5f83a6a..270d5bd 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -6604,6 +6604,12 @@ static void sctp_wake_up_waiters(struct sock *sk,
if (asoc->ep->sndbuf_policy)
return __sctp_write_space(asoc);
+ /* If association goes down and is just flushing its
+ * outq, then just normally notify others.
+ */
+ if (asoc->base.dead)
+ return sctp_write_space(sk);
+
/* Accounting for the sndbuf space is per socket, so we
* need to wake up others, try to be fair and in case of
* other associations, let them have a go first instead
--
1.7.11.7
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