Description

In the Linux kernel, the following vulnerability has been resolved: lib: test_hmm: evict device pages on file close to avoid use-after-free Patch series "Minor hmm_test fixes and cleanups". Two bugfixes a cleanup for the HMM kernel selftests. These were mostly reported by Zenghui Yu with special thanks to Lorenzo for analysing and pointing out the problems. This patch (of 3): When dmirror_fops_release() is called it frees the dmirror struct but doesn't migrate device private pages back to system memory first. This leaves those pages with a dangling zone_device_data pointer to the freed dmirror. If a subsequent fault occurs on those pages (eg. during coredump) the dmirror_devmem_fault() callback dereferences the stale pointer causing a kernel panic. This was reported [1] when running mm/ksft_hmm.sh on arm64, where a test failure triggered SIGABRT and the resulting coredump walked the VMAs faulting in the stale device private pages. Fix this by calling dmirror_device_evict_chunk() for each devmem chunk in dmirror_fops_release() to migrate all device private pages back to system memory before freeing the dmirror struct. The function is moved earlier in the file to avoid a forward declaration.

References 6

• git.kernel.org https://git.kernel.org/stable/c/234071b4318feaeb27cd2e4e1b16ef6b055adf89
• git.kernel.org https://git.kernel.org/stable/c/38f113f81d3f0adc658a4475dd3ecaec985e21d3
• git.kernel.org https://git.kernel.org/stable/c/5846715b6382dd4c6a69b35a56ca6115d33bc2a0
• git.kernel.org https://git.kernel.org/stable/c/744dd97752ef1076a8d8672bb0d8aa2c7abc1144
• git.kernel.org https://git.kernel.org/stable/c/9de1eb0aac2862d6144b8db0ec1388e79f8bc3e1
• git.kernel.org https://git.kernel.org/stable/c/bf477abd448c76bb8ea51c9b4f63a3a17c4b6239

Remediation