CVE-2024-53168: sunrpc: fix one UAF issue caused by sunrpc kernel tcp socket

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

sunrpc: fix one UAF issue caused by sunrpc kernel tcp socket

BUG: KASAN: slab-use-after-free in tcpwritetimerhandler+0x156/0x3e0 Read of size 1 at addr ffff888111f322cd by task swapper/0/0

CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.12.0-rc4-dirty #7 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 Call Trace: <IRQ> dumpstacklvl+0x68/0xa0 printaddressdescription.constprop.0+0x2c/0x3d0 printreport+0xb4/0x270 kasanreport+0xbd/0xf0 tcpwritetimerhandler+0x156/0x3e0 tcpwritetimer+0x66/0x170 calltimerfn+0xfb/0x1d0 runtimers+0x3f8/0x480 runtimersoftirq+0x9b/0x100 handlesoftirqs+0x153/0x390 irqexitrcu+0x103/0x120 irqexitrcu+0xe/0x20 sysvecapictimerinterrupt+0x76/0x90 </IRQ> <TASK> asmsysvecapictimerinterrupt+0x1a/0x20 RIP: 0010:defaultidle+0xf/0x20 Code: 4c 01 c7 4c 29 c2 e9 72 ff ff ff 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 f8 25 00 fb f4 <fa> c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 RSP: 0018:ffffffffa2007e28 EFLAGS: 00000242 RAX: 00000000000f3b31 RBX: 1ffffffff4400fc7 RCX: ffffffffa09c3196 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff9f00590f RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed102360835d R10: ffff88811b041aeb R11: 0000000000000001 R12: 0000000000000000 R13: ffffffffa202d7c0 R14: 0000000000000000 R15: 00000000000147d0 defaultidlecall+0x6b/0xa0 cpuidleidlecall+0x1af/0x1f0 doidle+0xbc/0x130 cpustartupentry+0x33/0x40 restinit+0x11f/0x210 startkernel+0x39a/0x420 x8664startreservations+0x18/0x30 x8664startkernel+0x97/0xa0 commonstartup64+0x13e/0x141 </TASK>

Allocated by task 595: kasansavestack+0x24/0x50 kasansavetrack+0x14/0x30 kasanslaballoc+0x87/0x90 kmemcacheallocnoprof+0x12b/0x3f0 copynetns+0x94/0x380 createnewnamespaces+0x24c/0x500 unsharensproxynamespaces+0x75/0xf0 ksysunshare+0x24e/0x4f0 x64sysunshare+0x1f/0x30 dosyscall64+0x70/0x180 entrySYSCALL64afterhwframe+0x76/0x7e

Freed by task 100: kasansavestack+0x24/0x50 kasansavetrack+0x14/0x30 kasansavefreeinfo+0x3b/0x60 kasanslabfree+0x54/0x70 kmemcachefree+0x156/0x5d0 cleanupnet+0x5d3/0x670 processonework+0x776/0xa90 workerthread+0x2e2/0x560 kthread+0x1a8/0x1f0 retfromfork+0x34/0x60 retfromforkasm+0x1a/0x30

Reproduction script:

mkdir -p /mnt/nfsshare mkdir -p /mnt/nfs/netns1 mkfs.ext4 /dev/sdb mount /dev/sdb /mnt/nfsshare systemctl restart nfs-server chmod 777 /mnt/nfsshare exportfs -i -o rw,norootsquash :/mnt/nfsshare

ip netns add netns1 ip link add name veth1peer type veth peer veth1 ifconfig veth1peer 11.11.0.254 up ip link set veth1 netns netns1 ip netns exec netns1 ifconfig veth1 11.11.0.1

ip netns exec netns1 /root/iptables -A OUTPUT -d 11.11.0.254 -p tcp \ --tcp-flags FIN FIN -j DROP

(note: In my environment, a DESTROYCLIENTID operation is always sent immediately, breaking the nfs tcp connection.) ip netns exec netns1 timeout -s 9 300 mount -t nfs -o proto=tcp,vers=4.1 \ 11.11.0.254:/mnt/nfsshare /mnt/nfs/netns1

ip netns del netns1

The reason here is that the tcp socket in netns1 (nfs side) has been shutdown and closed (done in xsdestroy), but the FIN message (with ack) is discarded, and the nfsd side keeps sending retransmission messages. As a result, when the tcp sock in netns1 processes the received message, it sends the message (FIN message) in the sending queue, and the tcp timer is re-established. When the network namespace is deleted, the net structure accessed by tcp's timer handler function causes problems.

To fix this problem, let's hold netns refcnt for the tcp kernel socket as done in other modules. This is an ugly hack which can easily be backported to earlier kernels. A proper fix which cleans up the interfaces will follow, but may not be so easy to backport.