[PATCH] proc: prevent a task from writing on its own /proc/*/mem

[Salvatore Mesoraca]

2018-05-26 17:48 GMT+02:00 Alexey Dobriyan <adobriyan at gmail.com>:
> On Sat, May 26, 2018 at 04:50:46PM +0200, Salvatore Mesoraca wrote:
>> Prevent a task from opening, in "write" mode, any /proc/*/mem
>> file that operates on the task's mm.
>> /proc/*/mem is mainly a debugging means and, as such, it shouldn't
>> be used by the inspected process itself.
>> Current implementation always allow a task to access its own
>> /proc/*/mem file.
>> A process can use it to overwrite read-only memory, making
>> pointless the use of security_file_mprotect() or other ways to
>> enforce RO memory.
>
> You can do it in security_ptrace_access_check()

No, because that hook is skipped when mm == current->mm:
https://elixir.bootlin.com/linux/v4.17-rc6/source/kernel/fork.c#L1111

> or security_file_open()

This is true, but it looks a bit overkill to me, especially since many of
the macros/functions used to handle proc's files won't be in scope
for an external LSM.
Is there any particular reason why you prefer it done via LSM?

Thank you,

Salvatore
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