CVE-2021-47591

In the Linux kernel, the following vulnerability has been resolved:

mptcp: remove tcp ulp setsockopt support

TCP_ULP setsockopt cannot be used for mptcp because its already used internally to plumb subflow (tcp) sockets to the mptcp layer.

syzbot managed to trigger a crash for mptcp connections that are in fallback mode:

KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027] CPU: 1 PID: 1083 Comm: syz-executor.3 Not tainted 5.16.0-rc2-syzkaller #0 RIP: 0010:tls_build_proto net/tls/tls_main.c:776 [inline] [..] __tcp_set_ulp net/ipv4/tcp_ulp.c:139 [inline] tcp_set_ulp+0x428/0x4c0 net/ipv4/tcp_ulp.c:160 do_tcp_setsockopt+0x455/0x37c0 net/ipv4/tcp.c:3391 mptcp_setsockopt+0x1b47/0x2400 net/mptcp/sockopt.c:638

Remove support for TCP_ULP setsockopt.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/3de0c86d42f841d1d64f316cd949e65c566f0734
• https://git.kernel.org/stable/c/404cd9a22150f24acf23a8df2ad0c094ba379f57
• https://git.kernel.org/stable/c/3de0c86d42f841d1d64f316cd949e65c566f0734
• https://git.kernel.org/stable/c/404cd9a22150f24acf23a8df2ad0c094ba379f57