CVE-2023-52885

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

SUNRPC: Fix UAF in svc_tcp_listen_data_ready()

After the listener svc_sock is freed, and before invoking svc_tcp_accept() for the established child sock, there is a window that the newsock retaining a freed listener svc_sock in sk_user_data which cloning from parent. In the race window, if data is received on the newsock, we will observe use-after-free report in svc_tcp_listen_data_ready().

Reproduce by two tasks:

1. while :; do rpc.nfsd 0 ; rpc.nfsd; done
2. while :; do echo | ncat -4 127.0.0.1 2049 ; done

KASAN report:

================================================================== BUG: KASAN: slab-use-after-free in svc_tcp_listen_data_ready+0x1cf/0x1f0 [sunrpc] Read of size 8 at addr ffff888139d96228 by task nc/102553 CPU: 7 PID: 102553 Comm: nc Not tainted 6.3.0+ #18 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 Call Trace: dump_stack_lvl+0x33/0x50 print_address_description.constprop.0+0x27/0x310 print_report+0x3e/0x70 kasan_report+0xae/0xe0 svc_tcp_listen_data_ready+0x1cf/0x1f0 [sunrpc] tcp_data_queue+0x9f4/0x20e0 tcp_rcv_established+0x666/0x1f60 tcp_v4_do_rcv+0x51c/0x850 tcp_v4_rcv+0x23fc/0x2e80 ip_protocol_deliver_rcu+0x62/0x300 ip_local_deliver_finish+0x267/0x350 ip_local_deliver+0x18b/0x2d0 ip_rcv+0x2fb/0x370 __netif_receive_skb_one_core+0x166/0x1b0 process_backlog+0x24c/0x5e0 __napi_poll+0xa2/0x500 net_rx_action+0x854/0xc90 __do_softirq+0x1bb/0x5de do_softirq+0xcb/0x100 …

Allocated by task 102371: kasan_save_stack+0x1e/0x40 kasan_set_track+0x21/0x30 __kasan_kmalloc+0x7b/0x90 svc_setup_socket+0x52/0x4f0 [sunrpc] svc_addsock+0x20d/0x400 [sunrpc] __write_ports_addfd+0x209/0x390 [nfsd] write_ports+0x239/0x2c0 [nfsd] nfsctl_transaction_write+0xac/0x110 [nfsd] vfs_write+0x1c3/0xae0 ksys_write+0xed/0x1c0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc

Freed by task 102551: kasan_save_stack+0x1e/0x40 kasan_set_track+0x21/0x30 kasan_save_free_info+0x2a/0x50 __kasan_slab_free+0x106/0x190 __kmem_cache_free+0x133/0x270 svc_xprt_free+0x1e2/0x350 [sunrpc] svc_xprt_destroy_all+0x25a/0x440 [sunrpc] nfsd_put+0x125/0x240 [nfsd] nfsd_svc+0x2cb/0x3c0 [nfsd] write_threads+0x1ac/0x2a0 [nfsd] nfsctl_transaction_write+0xac/0x110 [nfsd] vfs_write+0x1c3/0xae0 ksys_write+0xed/0x1c0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc

Fix the UAF by simply doing nothing in svc_tcp_listen_data_ready() if state != TCP_LISTEN, that will avoid dereferencing svsk for all child socket.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/42725e5c1b181b757ba11d804443922982334d9b
• https://git.kernel.org/stable/c/7e1f989055622fd086c5dfb291fc72adf5660b6f
• https://git.kernel.org/stable/c/c7b8c2d06e437639694abe76978e915cfb73f428
• https://git.kernel.org/stable/c/cd5ec3ee52ce4b7e283cc11facfa420c297c8065
• https://git.kernel.org/stable/c/dfc896c4a75cb8cd7cb2dfd9b469cf1e3f004254
• https://git.kernel.org/stable/c/ef047411887ff0845afd642d6a687819308e1a4e
• https://git.kernel.org/stable/c/fbf4ace39b2e4f3833236afbb2336edbafd75eee
• https://git.kernel.org/stable/c/fc80fc2d4e39137869da3150ee169b40bf879287
• https://git.kernel.org/stable/c/42725e5c1b181b757ba11d804443922982334d9b
• https://git.kernel.org/stable/c/7e1f989055622fd086c5dfb291fc72adf5660b6f
• https://git.kernel.org/stable/c/c7b8c2d06e437639694abe76978e915cfb73f428
• https://git.kernel.org/stable/c/cd5ec3ee52ce4b7e283cc11facfa420c297c8065
• https://git.kernel.org/stable/c/dfc896c4a75cb8cd7cb2dfd9b469cf1e3f004254
• https://git.kernel.org/stable/c/ef047411887ff0845afd642d6a687819308e1a4e
• https://git.kernel.org/stable/c/fbf4ace39b2e4f3833236afbb2336edbafd75eee
• https://git.kernel.org/stable/c/fc80fc2d4e39137869da3150ee169b40bf879287