Subject: CVE-2023-52523: bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets

With a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages
sent from one TCP socket (s1) to actually egress from another TCP
socket (s2):

tcp_bpf_sendmsg(s1)		// = sk_prot->sendmsg
  tcp_bpf_send_verdict(s1)	// __SK_REDIRECT case
    tcp_bpf_sendmsg_redir(s2)
      tcp_bpf_push_locked(s2)
	tcp_bpf_push(s2)
	  tcp_rate_check_app_limited(s2) // expects tcp_sock
	  tcp_sendmsg_locked(s2)	 // ditto

There is a hard-coded assumption in the call-chain, that the egress
socket (s2) is a TCP socket.

However in commit 122e6c79efe1 ("sock_map: Update sock type checks for
UDP") we have enabled redirects to non-TCP sockets. This was done for the
sake of BPF sk_skb programs. There was no indention to support sk_msg
send-to-egress use case.

As a result, attempts to send-to-egress through a non-TCP socket lead to a
crash due to invalid downcast from sock to tcp_sock:

 BUG: kernel NULL pointer dereference, address: 000000000000002f
 ...
 Call Trace:
  <TASK>
  ? show_regs+0x60/0x70
  ? __die+0x1f/0x70
  ? page_fault_oops+0x80/0x160
  ? do_user_addr_fault+0x2d7/0x800
  ? rcu_is_watching+0x11/0x50
  ? exc_page_fault+0x70/0x1c0
  ? asm_exc_page_fault+0x27/0x30
  ? tcp_tso_segs+0x14/0xa0
  tcp_write_xmit+0x67/0xce0
  __tcp_push_pending_frames+0x32/0xf0
  tcp_push+0x107/0x140
  tcp_sendmsg_locked+0x99f/0xbb0
  tcp_bpf_push+0x19d/0x3a0
  tcp_bpf_sendmsg_redir+0x55/0xd0
  tcp_bpf_send_verdict+0x407/0x550
  tcp_bpf_sendmsg+0x1a1/0x390
  inet_sendmsg+0x6a/0x70
  sock_sendmsg+0x9d/0xc0
  ? sockfd_lookup_light+0x12/0x80
  __sys_sendto+0x10e/0x160
  ? syscall_enter_from_user_mode+0x20/0x60
  ? __this_cpu_preempt_check+0x13/0x20
  ? lockdep_hardirqs_on+0x82/0x110
  __x64_sys_sendto+0x1f/0x30
  do_syscall_64+0x38/0x90
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reject selecting a non-TCP sockets as redirect target from a BPF sk_msg
program to prevent the crash. When attempted, user will receive an EACCES
error from send/sendto/sendmsg() syscall.

The Linux kernel CVE team has assigned CVE-2023-52523 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.13 with commit 122e6c79efe1 and fixed in 5.15.135 with commit bc8b89b69638
	Issue introduced in 5.13 with commit 122e6c79efe1 and fixed in 6.1.57 with commit b8f97e47b6fb
	Issue introduced in 5.13 with commit 122e6c79efe1 and fixed in 6.5.7 with commit ded6e448028f
	Issue introduced in 5.13 with commit 122e6c79efe1 and fixed in 6.6 with commit b80e31baa436

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2023-52523
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/core/sock_map.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/bc8b89b6963803a123f64aa9494155a037b3d728
	https://git.kernel.org/stable/c/b8f97e47b6fb84fcf2f5a22e725eefb6cf5070c2
	https://git.kernel.org/stable/c/ded6e448028f0f91b6af35985afca01fa02a9089
	https://git.kernel.org/stable/c/b80e31baa43614e086a9d29dc1151932b1bd7fc5