{"id":"CVE-2024-55916","summary":"Drivers: hv: util: Avoid accessing a ringbuffer not initialized yet","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nDrivers: hv: util: Avoid accessing a ringbuffer not initialized yet\n\nIf the KVP (or VSS) daemon starts before the VMBus channel's ringbuffer is\nfully initialized, we can hit the panic below:\n\nhv_utils: Registering HyperV Utility Driver\nhv_vmbus: registering driver hv_utils\n...\nBUG: kernel NULL pointer dereference, address: 0000000000000000\nCPU: 44 UID: 0 PID: 2552 Comm: hv_kvp_daemon Tainted: G E 6.11.0-rc3+ #1\nRIP: 0010:hv_pkt_iter_first+0x12/0xd0\nCall Trace:\n...\n vmbus_recvpacket\n hv_kvp_onchannelcallback\n vmbus_on_event\n tasklet_action_common\n tasklet_action\n handle_softirqs\n irq_exit_rcu\n sysvec_hyperv_stimer0\n \u003c/IRQ\u003e\n \u003cTASK\u003e\n asm_sysvec_hyperv_stimer0\n...\n kvp_register_done\n hvt_op_read\n vfs_read\n ksys_read\n __x64_sys_read\n\nThis can happen because the KVP/VSS channel callback can be invoked\neven before the channel is fully opened:\n1) as soon as hv_kvp_init() -\u003e hvutil_transport_init() creates\n/dev/vmbus/hv_kvp, the kvp daemon can open the device file immediately and\nregister itself to the driver by writing a message KVP_OP_REGISTER1 to the\nfile (which is handled by kvp_on_msg() -\u003ekvp_handle_handshake()) and\nreading the file for the driver's response, which is handled by\nhvt_op_read(), which calls hvt-\u003eon_read(), i.e. kvp_register_done().\n\n2) the problem with kvp_register_done() is that it can cause the\nchannel callback to be called even before the channel is fully opened,\nand when the channel callback is starting to run, util_probe()-\u003e\nvmbus_open() may have not initialized the ringbuffer yet, so the\ncallback can hit the panic of NULL pointer dereference.\n\nTo reproduce the panic consistently, we can add a \"ssleep(10)\" for KVP in\n__vmbus_open(), just before the first hv_ringbuffer_init(), and then we\nunload and reload the driver hv_utils, and run the daemon manually within\nthe 10 seconds.\n\nFix the panic by reordering the steps in util_probe() so the char dev\nentry used by the KVP or VSS daemon is not created until after\nvmbus_open() has completed. This reordering prevents the race condition\nfrom happening.","modified":"2026-04-16T04:40:06.062151929Z","published":"2025-01-11T12:35:44.800Z","related":["SUSE-SU-2025:0289-1","SUSE-SU-2025:0428-1","SUSE-SU-2025:0499-1","SUSE-SU-2025:0556-1","SUSE-SU-2025:0557-1","SUSE-SU-2025:0565-1","SUSE-SU-2025:0577-1","SUSE-SU-2025:0577-2","SUSE-SU-2025:20165-1","SUSE-SU-2025:20166-1","SUSE-SU-2025:20248-1","SUSE-SU-2025:20249-1","USN-7379-2","USN-7380-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/55xxx/CVE-2024-55916.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/042253c57be901bfd19f15b68267442b70f510d5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/07a756a49f4b4290b49ea46e089cbe6f79ff8d26"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3dd7a30c6d7f90afcf19e9b072f572ba524d7ec6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/718fe694a334be9d1a89eed22602369ac18d6583"},{"type":"WEB","url":"https://git.kernel.org/stable/c/89fcec5e466b3ac9b376e0d621c71effa1a7983f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d81f4e73aff9b861671df60e5100ad25cc16fbf8"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f091a224a2c82f1e302b1768d73bb6332f687321"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/55xxx/CVE-2024-55916.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-55916"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c"},{"fixed":"f091a224a2c82f1e302b1768d73bb6332f687321"},{"fixed":"d81f4e73aff9b861671df60e5100ad25cc16fbf8"},{"fixed":"042253c57be901bfd19f15b68267442b70f510d5"},{"fixed":"718fe694a334be9d1a89eed22602369ac18d6583"},{"fixed":"89fcec5e466b3ac9b376e0d621c71effa1a7983f"},{"fixed":"3dd7a30c6d7f90afcf19e9b072f572ba524d7ec6"},{"fixed":"07a756a49f4b4290b49ea46e089cbe6f79ff8d26"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-55916.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}