CVE-2023-52885

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

SUNRPC: Fix UAF in svctcplistendataready()

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

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 svctcplistendataready+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: <IRQ> dumpstacklvl+0x33/0x50 printaddressdescription.constprop.0+0x27/0x310 printreport+0x3e/0x70 kasanreport+0xae/0xe0 svctcplistendataready+0x1cf/0x1f0 [sunrpc] tcpdataqueue+0x9f4/0x20e0 tcprcvestablished+0x666/0x1f60 tcpv4dorcv+0x51c/0x850 tcpv4rcv+0x23fc/0x2e80 ipprotocoldeliverrcu+0x62/0x300 iplocaldeliverfinish+0x267/0x350 iplocaldeliver+0x18b/0x2d0 iprcv+0x2fb/0x370 __netifreceiveskb_onecore+0x166/0x1b0 processbacklog+0x24c/0x5e0 __napipoll+0xa2/0x500 netrx_action+0x854/0xc90 __dosoftirq+0x1bb/0x5de dosoftirq+0xcb/0x100 </IRQ> <TASK> ... </TASK>

Allocated by task 102371: kasansavestack+0x1e/0x40 kasansettrack+0x21/0x30 __kasankmalloc+0x7b/0x90 svcsetupsocket+0x52/0x4f0 [sunrpc] svcaddsock+0x20d/0x400 [sunrpc] _writeportsaddfd+0x209/0x390 [nfsd] writeports+0x239/0x2c0 [nfsd] nfsctltransactionwrite+0xac/0x110 [nfsd] vfswrite+0x1c3/0xae0 ksyswrite+0xed/0x1c0 dosyscall64+0x38/0x90 entrySYSCALL64afterhwframe+0x72/0xdc

Freed by task 102551: kasansavestack+0x1e/0x40 kasansettrack+0x21/0x30 kasansavefree_info+0x2a/0x50 __kasanslabfree+0x106/0x190 __kmemcachefree+0x133/0x270 svcxprtfree+0x1e2/0x350 [sunrpc] svcxprtdestroyall+0x25a/0x440 [sunrpc] nfsdput+0x125/0x240 [nfsd] nfsdsvc+0x2cb/0x3c0 [nfsd] writethreads+0x1ac/0x2a0 [nfsd] nfsctltransactionwrite+0xac/0x110 [nfsd] vfswrite+0x1c3/0xae0 ksyswrite+0xed/0x1c0 dosyscall64+0x38/0x90 entrySYSCALL64afterhwframe+0x72/0xdc

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