CVE-2023-52523

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.