CVE-2023-52523

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets<br /> <br /> With a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages<br /> sent from one TCP socket (s1) to actually egress from another TCP<br /> socket (s2):<br /> <br /> tcp_bpf_sendmsg(s1) // = sk_prot-&gt;sendmsg<br /> tcp_bpf_send_verdict(s1) // __SK_REDIRECT case<br /> tcp_bpf_sendmsg_redir(s2)<br /> tcp_bpf_push_locked(s2)<br /> tcp_bpf_push(s2)<br /> tcp_rate_check_app_limited(s2) // expects tcp_sock<br /> tcp_sendmsg_locked(s2) // ditto<br /> <br /> There is a hard-coded assumption in the call-chain, that the egress<br /> socket (s2) is a TCP socket.<br /> <br /> However in commit 122e6c79efe1 ("sock_map: Update sock type checks for<br /> UDP") we have enabled redirects to non-TCP sockets. This was done for the<br /> sake of BPF sk_skb programs. There was no indention to support sk_msg<br /> send-to-egress use case.<br /> <br /> As a result, attempts to send-to-egress through a non-TCP socket lead to a<br /> crash due to invalid downcast from sock to tcp_sock:<br /> <br /> BUG: kernel NULL pointer dereference, address: 000000000000002f<br /> ...<br /> Call Trace:<br /> <br /> ? show_regs+0x60/0x70<br /> ? __die+0x1f/0x70<br /> ? page_fault_oops+0x80/0x160<br /> ? do_user_addr_fault+0x2d7/0x800<br /> ? rcu_is_watching+0x11/0x50<br /> ? exc_page_fault+0x70/0x1c0<br /> ? asm_exc_page_fault+0x27/0x30<br /> ? tcp_tso_segs+0x14/0xa0<br /> tcp_write_xmit+0x67/0xce0<br /> __tcp_push_pending_frames+0x32/0xf0<br /> tcp_push+0x107/0x140<br /> tcp_sendmsg_locked+0x99f/0xbb0<br /> tcp_bpf_push+0x19d/0x3a0<br /> tcp_bpf_sendmsg_redir+0x55/0xd0<br /> tcp_bpf_send_verdict+0x407/0x550<br /> tcp_bpf_sendmsg+0x1a1/0x390<br /> inet_sendmsg+0x6a/0x70<br /> sock_sendmsg+0x9d/0xc0<br /> ? sockfd_lookup_light+0x12/0x80<br /> __sys_sendto+0x10e/0x160<br /> ? syscall_enter_from_user_mode+0x20/0x60<br /> ? __this_cpu_preempt_check+0x13/0x20<br /> ? lockdep_hardirqs_on+0x82/0x110<br /> __x64_sys_sendto+0x1f/0x30<br /> do_syscall_64+0x38/0x90<br /> entry_SYSCALL_64_after_hwframe+0x63/0xcd<br /> <br /> Reject selecting a non-TCP sockets as redirect target from a BPF sk_msg<br /> program to prevent the crash. When attempted, user will receive an EACCES<br /> error from send/sendto/sendmsg() syscall.