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Message-ID: <2025011146-CVE-2024-55916-3a1f@gregkh> Date: Sat, 11 Jan 2025 13:35:56 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: CVE-2024-55916: Drivers: hv: util: Avoid accessing a ringbuffer not initialized yet Description =========== In the Linux kernel, the following vulnerability has been resolved: Drivers: hv: util: Avoid accessing a ringbuffer not initialized yet If the KVP (or VSS) daemon starts before the VMBus channel's ringbuffer is fully initialized, we can hit the panic below: hv_utils: Registering HyperV Utility Driver hv_vmbus: registering driver hv_utils ... BUG: kernel NULL pointer dereference, address: 0000000000000000 CPU: 44 UID: 0 PID: 2552 Comm: hv_kvp_daemon Tainted: G E 6.11.0-rc3+ #1 RIP: 0010:hv_pkt_iter_first+0x12/0xd0 Call Trace: ... vmbus_recvpacket hv_kvp_onchannelcallback vmbus_on_event tasklet_action_common tasklet_action handle_softirqs irq_exit_rcu sysvec_hyperv_stimer0 </IRQ> <TASK> asm_sysvec_hyperv_stimer0 ... kvp_register_done hvt_op_read vfs_read ksys_read __x64_sys_read This can happen because the KVP/VSS channel callback can be invoked even before the channel is fully opened: 1) as soon as hv_kvp_init() -> hvutil_transport_init() creates /dev/vmbus/hv_kvp, the kvp daemon can open the device file immediately and register itself to the driver by writing a message KVP_OP_REGISTER1 to the file (which is handled by kvp_on_msg() ->kvp_handle_handshake()) and reading the file for the driver's response, which is handled by hvt_op_read(), which calls hvt->on_read(), i.e. kvp_register_done(). 2) the problem with kvp_register_done() is that it can cause the channel callback to be called even before the channel is fully opened, and when the channel callback is starting to run, util_probe()-> vmbus_open() may have not initialized the ringbuffer yet, so the callback can hit the panic of NULL pointer dereference. To reproduce the panic consistently, we can add a "ssleep(10)" for KVP in __vmbus_open(), just before the first hv_ringbuffer_init(), and then we unload and reload the driver hv_utils, and run the daemon manually within the 10 seconds. Fix the panic by reordering the steps in util_probe() so the char dev entry used by the KVP or VSS daemon is not created until after vmbus_open() has completed. This reordering prevents the race condition from happening. The Linux kernel CVE team has assigned CVE-2024-55916 to this issue. Affected and fixed versions =========================== Issue introduced in 4.9 with commit e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c and fixed in 5.4.289 with commit f091a224a2c82f1e302b1768d73bb6332f687321 Issue introduced in 4.9 with commit e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c and fixed in 5.10.233 with commit d81f4e73aff9b861671df60e5100ad25cc16fbf8 Issue introduced in 4.9 with commit e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c and fixed in 5.15.176 with commit 042253c57be901bfd19f15b68267442b70f510d5 Issue introduced in 4.9 with commit e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c and fixed in 6.1.122 with commit 718fe694a334be9d1a89eed22602369ac18d6583 Issue introduced in 4.9 with commit e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c and fixed in 6.6.68 with commit 89fcec5e466b3ac9b376e0d621c71effa1a7983f Issue introduced in 4.9 with commit e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c and fixed in 6.12.7 with commit 3dd7a30c6d7f90afcf19e9b072f572ba524d7ec6 Issue introduced in 4.9 with commit e0fa3e5e7df61eb2c339c9f0067c202c0cdeec2c and fixed in 6.13-rc4 with commit 07a756a49f4b4290b49ea46e089cbe6f79ff8d26 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2024-55916 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: drivers/hv/hv_kvp.c drivers/hv/hv_snapshot.c drivers/hv/hv_util.c drivers/hv/hyperv_vmbus.h include/linux/hyperv.h Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/f091a224a2c82f1e302b1768d73bb6332f687321 https://git.kernel.org/stable/c/d81f4e73aff9b861671df60e5100ad25cc16fbf8 https://git.kernel.org/stable/c/042253c57be901bfd19f15b68267442b70f510d5 https://git.kernel.org/stable/c/718fe694a334be9d1a89eed22602369ac18d6583 https://git.kernel.org/stable/c/89fcec5e466b3ac9b376e0d621c71effa1a7983f https://git.kernel.org/stable/c/3dd7a30c6d7f90afcf19e9b072f572ba524d7ec6 https://git.kernel.org/stable/c/07a756a49f4b4290b49ea46e089cbe6f79ff8d26
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