[PATCH] dccp: don't duplicate ccid when cloning dccp sock

Commit 2677d2067731 ("dccp: don't free ccid2_hc_tx_sock ...") fixed
a UAF but reintroduced CVE-2017-6074.

When the sock is cloned, two dccps_hc_tx_ccid will reference to the
same ccid. So one can free the ccid object twice from two socks after
cloning.

This issue was found by "Hadar Manor" as well and assigned with
CVE-2020-16119, which was fixed in Ubuntu's kernel. So here I port
the patch from Ubuntu to fix it.

The patch prevents cloned socks from referencing the same ccid.

Fixes: 2677d2067731410 ("dccp: don't free ccid2_hc_tx_sock ...")
Signed-off-by: Zhenpeng Lin <redacted>
---
 net/dccp/minisocks.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index c5c74a34d139..91e7a2202697 100644
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c

@@ -94,6 +94,8 @@ struct sock *dccp_create_openreq_child(const struct sock *sk,
 		newdp->dccps_role	    = DCCP_ROLE_SERVER;
 		newdp->dccps_hc_rx_ackvec   = NULL;
 		newdp->dccps_service_list   = NULL;
+		newdp->dccps_hc_rx_ccid     = NULL;
+		newdp->dccps_hc_tx_ccid     = NULL;
 		newdp->dccps_service	    = dreq->dreq_service;
 		newdp->dccps_timestamp_echo = dreq->dreq_timestamp_echo;
 		newdp->dccps_timestamp_time = dreq->dreq_timestamp_time;
--

2.25.1

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Wed, 8 Sep 2021 03:40:59 +0000 you wrote:

Commit 2677d2067731 ("dccp: don't free ccid2_hc_tx_sock ...") fixed
a UAF but reintroduced CVE-2017-6074.

When the sock is cloned, two dccps_hc_tx_ccid will reference to the
same ccid. So one can free the ccid object twice from two socks after
cloning.

[...]

Here is the summary with links:
  - dccp: don't duplicate ccid when cloning dccp sock
    https://git.kernel.org/netdev/net/c/d9ea761fdd19

You are awesome, thank you!
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