CVE-2023-52849

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

cxl/mem: Fix shutdown order

Ira reports that removing cxl_mock_mem causes a crash with the following trace:

BUG: kernel NULL pointer dereference, address: 0000000000000044 [..] RIP: 0010:cxl_region_decode_reset+0x7f/0x180 [cxl_core] [..] Call Trace: cxl_region_detach+0xe8/0x210 [cxl_core] cxl_decoder_kill_region+0x27/0x40 [cxl_core] cxld_unregister+0x29/0x40 [cxl_core] devres_release_all+0xb8/0x110 device_unbind_cleanup+0xe/0x70 device_release_driver_internal+0x1d2/0x210 bus_remove_device+0xd7/0x150 device_del+0x155/0x3e0 device_unregister+0x13/0x60 devm_release_action+0x4d/0x90 ? __pfx_unregister_port+0x10/0x10 [cxl_core] delete_endpoint+0x121/0x130 [cxl_core] devres_release_all+0xb8/0x110 device_unbind_cleanup+0xe/0x70 device_release_driver_internal+0x1d2/0x210 bus_remove_device+0xd7/0x150 device_del+0x155/0x3e0 ? lock_release+0x142/0x290 cdev_device_del+0x15/0x50 cxl_memdev_unregister+0x54/0x70 [cxl_core]

This crash is due to the clearing out the cxl_memdevs driver context (@cxlds) before the subsystem is done with it. This is ultimately due to the region(s), that this memdev is a member, being torn down and expecting to be able to de-reference @cxlds, like here:

static int cxl_region_decode_reset(struct cxl_region *cxlr, int count) … if (cxlds->rcd) goto endpoint_reset; …

Fix it by keeping the driver context valid until memdev-device unregistration, and subsequently the entire stack of related dependencies, unwinds.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0ca074f7d788627a4e0b047ca5fbdb5fc567220c
• https://git.kernel.org/stable/c/20bd0198bebdd706bd4614b3933ef70d7c19618f
• https://git.kernel.org/stable/c/7c7371b41a14e86f53e7dbe5baa7b1d3e0ab324b
• https://git.kernel.org/stable/c/88d3917f82ed4215a2154432c26de1480a61b209
• https://git.kernel.org/stable/c/cad22a757029c3a1985c221a2d4a6491ad4035ae
• https://git.kernel.org/stable/c/0ca074f7d788627a4e0b047ca5fbdb5fc567220c
• https://git.kernel.org/stable/c/20bd0198bebdd706bd4614b3933ef70d7c19618f
• https://git.kernel.org/stable/c/7c7371b41a14e86f53e7dbe5baa7b1d3e0ab324b
• https://git.kernel.org/stable/c/88d3917f82ed4215a2154432c26de1480a61b209
• https://git.kernel.org/stable/c/cad22a757029c3a1985c221a2d4a6491ad4035ae