CVE-2021-46959

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

spi: Fix use-after-free with devm_spi_alloc_*

We cant rely on the contents of the devres list during spi_unregister_controller(), as the list is already torn down at the time we perform devres_find() for devm_spi_release_controller. This causes devices registered with devm_spi_alloc_{master,slave}() to be mistakenly identified as legacy, non-devm managed devices and have their reference counters decremented below 0.

————[ cut here ]———— WARNING: CPU: 1 PID: 660 at lib/refcount.c:28 refcount_warn_saturate+0x108/0x174 [] (refcount_warn_saturate) from [] (kobject_put+0x90/0x98) [] (kobject_put) from [] (put_device+0x20/0x24) r4:b6700140 [] (put_device) from [] (devm_spi_release_controller+0x3c/0x40) [] (devm_spi_release_controller) from [] (release_nodes+0x84/0xc4) r5:b6700180 r4:b6700100 [] (release_nodes) from [] (devres_release_all+0x5c/0x60) r8:b1638c54 r7:b117ad94 r6:b1638c10 r5:b117ad94 r4:b163dc10 [] (devres_release_all) from [] (__device_release_driver+0x144/0x1ec) r5:b117ad94 r4:b163dc10 [] (__device_release_driver) from [] (device_driver_detach+0x84/0xa0) r9:00000000 r8:00000000 r7:b117ad94 r6:b163dc54 r5:b1638c10 r4:b163dc10 [] (device_driver_detach) from [] (unbind_store+0xe4/0xf8)

Instead, determine the devm allocation state as a flag on the controller which is guaranteed to be stable during cleanup.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/001c8e83646ad3b847b18f6ac55a54367d917d74
• https://git.kernel.org/stable/c/28a5529068c51cdf0295ab1e11a99a3a909a03e4
• https://git.kernel.org/stable/c/62bb2c7f2411a0045c24831f11ecacfc35610815
• https://git.kernel.org/stable/c/794aaf01444d4e765e2b067cba01cc69c1c68ed9
• https://git.kernel.org/stable/c/8735248ebb918d25427965f0db07939ed0473ec6
• https://git.kernel.org/stable/c/8bf96425c90f5c1dcf3b7b9df568019a1d4b8a0e
• https://git.kernel.org/stable/c/8e029707f50a82c53172359c686b2536ab54e58c
• https://git.kernel.org/stable/c/c7fabe372a9031acd00498bc718ce27c253abfd1
• https://git.kernel.org/stable/c/cee78aa24578edac8cf00513dca618c0acc17cd7
• https://git.kernel.org/stable/c/001c8e83646ad3b847b18f6ac55a54367d917d74
• https://git.kernel.org/stable/c/28a5529068c51cdf0295ab1e11a99a3a909a03e4
• https://git.kernel.org/stable/c/62bb2c7f2411a0045c24831f11ecacfc35610815
• https://git.kernel.org/stable/c/794aaf01444d4e765e2b067cba01cc69c1c68ed9
• https://git.kernel.org/stable/c/8735248ebb918d25427965f0db07939ed0473ec6
• https://git.kernel.org/stable/c/8bf96425c90f5c1dcf3b7b9df568019a1d4b8a0e
• https://git.kernel.org/stable/c/8e029707f50a82c53172359c686b2536ab54e58c
• https://git.kernel.org/stable/c/c7fabe372a9031acd00498bc718ce27c253abfd1
• https://git.kernel.org/stable/c/cee78aa24578edac8cf00513dca618c0acc17cd7