CVE-2021-47593 Information

Description

In the Linux kernel the following vulnerability has been resolved:

mptcp: clear ‘kern’ flag from fallback sockets

The mptcp ULP extension relies on sk->sk_sock_kern being set correctly: It prevents setsockopt(fd IPPROTO_TCP TCP_ULP \mptcp\ 6); from working for plain tcp sockets (any userspace-exposed socket).

But in case of fallback accept() can return a plain tcp sk. In such case sk is still tagged as ‘kernel’ and setsockopt will work.

This will crash the kernel The subflow extension has a NULL ctx->conn mptcp socket:

BUG: KASAN: null-ptr-deref in subflow_data_ready+0x181/0x2b0 Call Trace: tcp_data_ready+0xf8/0x370 [..]

Reference

https://git.kernel.org/stable/c/451f1eded7f56e93aaf52eb547ba97742d9c0e97 https://git.kernel.org/stable/c/c26ac0ea3a91c210cf90452e625dc441adf3e549 https://git.kernel.org/stable/c/d6692b3b97bdc165d150f4c1505751a323a80717