Checkpoint/Restore: Show in proc IDs of objects that can be shared between tasks
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- v2 Latest3 of 4 patches 17 repliesIn review
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3 of 4 patches are in this archive. The cover letter announces 4.
Patches in v2 No applies recorded yet
| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 1/4 | Routine for generating a safe ID for kernel pointerinclude/ mm/ mm/ | +48 | 0 replies | |
| 2/4 | proc: Show namespaces IDs in /proc/pid/ns/* filesfs/ include/ | +13 | 0 replies | |
| 3/4 | proc: Show open file ID in /proc/pid/fdinfo/*fs/ include/ | +5 | 0 replies |
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Cover letter [PATCH v2 0/4] Checkpoint/Restore: Show in proc IDs of objects that can be shared between tasks
While doing the checkpoint-restore in the userspace one need to determine whether various kernel objects (like mm_struct-s of file_struct-s) are shared between tasks and restore this state.
The 2nd step can for now be solved by using respective CLONE_XXX flags and the unshare syscall, while there's currently no ways for solving the 1st one.
One of the ways for checking whether two tasks share e.g. an mm_struct is to provide some mm_struct ID of a task to its proc file. The best from the performance point of view ID is the object address in the kernel, but showing them to the userspace is not good for security reasons.
Thus the object address is XOR-ed with a "random" value of the same size and then shown in proc. Providing this poison is not leaked into the userspace then ID seem to be safe. The objects for which the IDs are shown are:
* all namespaces living in /proc/pid/ns/
* open files (shown in /proc/pid/fdinfo/)
* objects, that can be shared with CLONE_XXX flags (except for namespaces)
Changes since
v1: * Tejun worried about the single poison value was a weak side - leaking one
makes all the IDs vulnerable. To address this several poison values - one per object type - are introduced. They are stored in a plain array. Tejun, is this enough from your POV, or you'd like to see them widely scattered over the memory?
* Pekka proposed to initialized poison values in the late_initcall callback
* ... and move the code to mm/util.c