From: Yonglong Li liyonglong@chinatelecom.cn

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") Cc: stable@vger.kernel.org Reviewed-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Yonglong Li liyonglong@chinatelecom.cn Signed-off-by: Mat Martineau mathew.j.martineau@linux.intel.com --- 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); kfree_skb(skb); return NULL; }

base-commit: 551acdc3c3d2b6bc97f11e31dcf960bc36343bfc