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