CVE-2023-52609

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

binder: fix race between mmput() and do_exit()

Task A calls binder_update_page_range() to allocate and insert pages on a remote address space from Task B. For this, Task A pins the remote mm via mmget_not_zero() first. This can race with Task B do_exit() and the final mmput() refcount decrement will come from Task A.

Task A | Task B ——————+—————— mmget_not_zero() | | do_exit() | exit_mm() | mmput() mmput() | exit_mmap() | remove_vma() | fput() |

In this case, the work of ____fput() from Task B is queued up in Task A as TWA_RESUME. So in theory, Task A returns to userspace and the cleanup work gets executed. However, Task A instead sleep, waiting for a reply from Task B that never comes (its dead).

This means the binder_deferred_release() is blocked until an unrelated binder event forces Task A to go back to userspace. All the associated death notifications will also be delayed until then.

In order to fix this use mmput_async() that will schedule the work in the corresponding mm->async_put_work WQ instead of Task A.

Affected Software

References

• https://git.kernel.org/stable/c/252a2a5569eb9f8d16428872cc24dea1ac0bb097
• https://git.kernel.org/stable/c/6696f76c32ff67fec26823fc2df46498e70d9bf3
• https://git.kernel.org/stable/c/67f16bf2cc1698fd50e01ee8a2becc5a8e6d3a3e
• https://git.kernel.org/stable/c/77d210e8db4d61d43b2d16df66b1ec46fad2ee01
• https://git.kernel.org/stable/c/7e7a0d86542b0ea903006d3f42f33c4f7ead6918
• https://git.kernel.org/stable/c/95b1d336b0642198b56836b89908d07b9a0c9608
• https://git.kernel.org/stable/c/98fee5bee97ad47b527a997d5786410430d1f0e9
• https://git.kernel.org/stable/c/9a9ab0d963621d9d12199df9817e66982582d5a5
• https://git.kernel.org/stable/c/252a2a5569eb9f8d16428872cc24dea1ac0bb097
• https://git.kernel.org/stable/c/6696f76c32ff67fec26823fc2df46498e70d9bf3
• https://git.kernel.org/stable/c/67f16bf2cc1698fd50e01ee8a2becc5a8e6d3a3e
• https://git.kernel.org/stable/c/77d210e8db4d61d43b2d16df66b1ec46fad2ee01
• https://git.kernel.org/stable/c/7e7a0d86542b0ea903006d3f42f33c4f7ead6918
• https://git.kernel.org/stable/c/95b1d336b0642198b56836b89908d07b9a0c9608
• https://git.kernel.org/stable/c/98fee5bee97ad47b527a997d5786410430d1f0e9
• https://git.kernel.org/stable/c/9a9ab0d963621d9d12199df9817e66982582d5a5
• https://lists.debian.org/debian-lts-announce/2024/06/msg00016.html
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html