[PATCH 5.17 0688/1126] mptcp: Fix crash due to tcp_tsorted_anchor was initialized before release skb

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 05:52:55 EST

From: Yonglong Li <liyonglong@xxxxxxxxxxxxxxx>

[ Upstream commit 3ef3905aa3b5b3e222ee6eb0210bfd999417a8cc ]

Got crash when doing pressure test of mptcp:

dst_release: dst:ffffa06ce6e5c058 refcnt:-1
kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
BUG: unable to handle kernel paging request at ffffa06ce6e5c058
PGD 190a01067 P4D 190a01067 PUD 43fffb067 PMD 22e403063 PTE 8000000226e5c063
Oops: 0011 [#1] SMP PTI
CPU: 7 PID: 7823 Comm: kworker/7:0 Kdump: loaded Tainted: G E
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.2.1 04/01/2014
Call Trace:
? skb_release_head_state+0x68/0x100
? skb_release_all+0xe/0x30
? kfree_skb+0x32/0xa0
? mptcp_sendmsg_frag+0x57e/0x750
? __mptcp_retrans+0x21b/0x3c0
? __switch_to_asm+0x35/0x70
? mptcp_worker+0x25e/0x320
? process_one_work+0x1a7/0x360
? worker_thread+0x30/0x390
? create_worker+0x1a0/0x1a0
? kthread+0x112/0x130
? kthread_flush_work_fn+0x10/0x10
? ret_from_fork+0x35/0x40

In __mptcp_alloc_tx_skb skb was allocated and skb->tcp_tsorted_anchor will
be initialized, in under memory pressure situation sk_wmem_schedule will
return false and then kfree_skb. In this case skb->_skb_refdst is not null
because_skb_refdst and tcp_tsorted_anchor are stored in the same mem, and
kfree_skb will try to release dst and cause crash.

Fixes: f70cad1085d1 ("mptcp: stop relying on tcp_tx_skb_cache")
Reviewed-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Yonglong Li <liyonglong@xxxxxxxxxxxxxxx>
Signed-off-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220317220953.426024-1-mathew.j.martineau@xxxxxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
net/mptcp/protocol.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 1c72f25f083e..014c9d88f947 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1196,6 +1196,7 @@ static struct sk_buff *__mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, g
tcp_skb_entail(ssk, skb);
return skb;
+ tcp_skb_tsorted_anchor_cleanup(skb);
return NULL;