Hello, A user erroneously sent me a refcount UaF in NFS with 5.6-rc6. I thought I should forward it onward here in case this is not already known. The original reporter is CC'd in case you have any questions. Regards, Jason -------8<------------------------ Mar 20 21:43:34 agro kernel: ------------[ cut here ]------------ Mar 20 21:43:34 agro kernel: refcount_t: underflow; use-after-free. Mar 20 21:43:34 agro kernel: WARNING: CPU: 1 PID: 9334 at lib/refcount.c:28 refcount_warn_saturate+0xd9/0xe0 Mar 20 21:43:34 agro kernel: Modules linked in: md5 wireguard curve25519_x86_64 libcurve25519_generic libchacha20poly1305 chacha_x86_64 libchacha poly1305_x86_64 ip6_udp_tunnel udp_tunnel libblake2s blake2s_x86_64 libblake2s_generic xt_mac xt_nat xt_MASQUERADE xt_REDIRECT xt_owner xt_comment ipt_REJECT nf_reject_ipv4 xt_mark xt_hashlimit xt_multiport nfnetlink_log xt_NFLOG nf_log_ipv4 nf_log_common xt_LOG nf_nat_tftp nf_nat_sip nf_nat_h323 nf_nat_ftp nf_conntrack_tftp nf_conntrack_sip nf_conntrack_netlink nfnetlink nf_conntrack_h323 nf_conntrack_ftp nfsd auth_rpcgss nfs_acl lockd grace sunrpc cpufreq_ondemand msr bridge stp llc xt_tcpudp xt_conntrack iptable_mangle iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_raw iptable_filter ip_tables x_tables btrfs blake2b_generic xor raid6_pq libcrc32c zstd_compress zstd_decompress zlib_deflate zlib_inflate uas usb_storage snd_hda_codec_realtek snd_hda_codec_generic matroxfb_base matroxfb_g450 matroxfb_Ti3026 snd_hda_int el matroxfb_accel Mar 20 21:43:34 agro kernel: snd_intel_dspcfg cfbfillrect cfbimgblt atlantic snd_hda_codec r8169 cfbcopyarea e1000e snd_hda_core snd_hwdep matroxfb_DAC1064 g450_pll matroxfb_misc ptp realtek fb snd_pcm libphy snd_timer mxm_wmi xhci_pci pcspkr i2c_piix4 input_leds pps_core fbdev k10temp ohci_pci snd xhci_hcd ohci_hcd ehci_pci soundcore i2c_core ehci_hcd wmi acpi_cpufreq vhci_hcd usbip_core usbcore usb_common vhost_net vhost kvm_amd kvm irqbypass loop tun fuse it87 hwmon_vid hwmon Mar 20 21:43:34 agro kernel: CPU: 1 PID: 9334 Comm: kworker/u16:3 Not tainted 5.6.0-rc6 #1 Mar 20 21:43:34 agro kernel: Hardware name: Gigabyte Technology Co., Ltd. GA-990FXA-UD5/GA-990FXA-UD5, BIOS F12 10/03/2013 Mar 20 21:43:34 agro kernel: Workqueue: rpciod rpc_async_schedule [sunrpc] Mar 20 21:43:34 agro kernel: RIP: 0010:refcount_warn_saturate+0xd9/0xe0 Mar 20 21:43:34 agro kernel: Code: ff 48 c7 c7 e8 ff d5 81 c6 05 cd 49 b5 00 01 e8 4d 04 cf ff 0f 0b c3 48 c7 c7 90 ff d5 81 c6 05 b9 49 b5 00 01 e8 37 04 cf ff <0f> 0b c3 0f 1f 40 00 8b 07 3d 00 00 00 c0 74 12 83 f8 01 74 46 8d Mar 20 21:43:34 agro kernel: RSP: 0018:ffffc900010dfde0 EFLAGS: 00010282 Mar 20 21:43:34 agro kernel: RAX: 0000000000000026 RBX: 0000000000000e81 RCX: 0000000000000007 Mar 20 21:43:34 agro kernel: RDX: 0000000000000007 RSI: 0000000000000092 RDI: ffff88881fc587c0 Mar 20 21:43:34 agro kernel: RBP: ffff8887eeb40470 R08: 00000000000004d9 R09: 0000000000000001 Mar 20 21:43:34 agro kernel: R10: 0000000000000000 R11: 0000000000000001 R12: ffff8884f1e28510 Mar 20 21:43:34 agro kernel: R13: ffff88837dc49f30 R14: 0000000000000001 R15: ffff888780b8a840 Mar 20 21:43:34 agro kernel: FS: 0000000000000000(0000) GS:ffff88881fc40000(0000) knlGS:0000000000000000 Mar 20 21:43:34 agro kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Mar 20 21:43:34 agro kernel: CR2: 000000000421efb0 CR3: 0000000510564000 CR4: 00000000000006e0 Mar 20 21:43:34 agro kernel: Call Trace: Mar 20 21:43:34 agro kernel: nfsd41_destroy_cb+0x36/0x50 [nfsd] Mar 20 21:43:34 agro kernel: rpc_free_task+0x3c/0x70 [sunrpc] Mar 20 21:43:34 agro kernel: __rpc_execute+0x3a5/0x3c0 [sunrpc] Mar 20 21:43:34 agro kernel: ? finish_task_switch+0x7f/0x250 Mar 20 21:43:34 agro kernel: rpc_async_schedule+0x2f/0x50 [sunrpc] Mar 20 21:43:34 agro kernel: process_one_work+0x1ca/0x3c0 Mar 20 21:43:34 agro kernel: worker_thread+0x45/0x3d0 Mar 20 21:43:34 agro kernel: kthread+0xf3/0x130 Mar 20 21:43:34 agro kernel: ? process_one_work+0x3c0/0x3c0 Mar 20 21:43:34 agro kernel: ? kthread_park+0x80/0x80 Mar 20 21:43:34 agro kernel: ret_from_fork+0x1f/0x30 Mar 20 21:43:34 agro kernel: ---[ end trace 99765c8e28c46274 ]---
