Re: [PATCH 0/5] Rust support for `struct iov_iter`

[Andreas Hindborg]

"Greg Kroah-Hartman" <gregkh@xxxxxxxxxxxxxxxxxxx> writes:

> On Tue, Mar 11, 2025 at 02:25:11PM +0000, Alice Ryhl wrote:
>> This series adds support for the `struct iov_iter` type. This type
>> represents an IO buffer for reading or writing, and can be configured
>> for either direction of communication.
>>
>> In Rust, we define separate types for reading and writing. This will
>> ensure that you cannot mix them up and e.g. call copy_from_iter in a
>> read_iter syscall.
>>
>> To use the new abstractions, miscdevices are given new methods read_iter
>> and write_iter that can be used to implement the read/write syscalls on
>> a miscdevice. The miscdevice sample is updated to provide read/write
>> operations.
>
> Nice, this is good to have, but what's the odds of tieing in the
> "untrusted buffer" logic here so that all misc drivers HAVE to properly
> validate the data sent to them before they can touch it:
> 	https://lore.kernel.org/r/20240925205244.873020-1-benno.lossin@xxxxxxxxx
>
> I'd like to force drivers to do this, otherwise it's just going to force
> us to audit all paths from userspace->kernel that happen.
>

I think that for user backed iterators (`user_backed_iter(iter) != 0`)
we will have the same problems as discussed in [1]. To validate, we
would have to copy the data to another buffer and then validate it
there, in a race free place. But the copying is apparently a problem.


Best regards,
Andreas Hindborg


[1] https://lore.kernel.org/all/ab8fd525-9a63-46e2-a443-b9d94eed6004@xxxxxxxx/