linux-kernel - Accessing user-land memory without safe functions

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Date:	Thu, 3 Dec 2015 13:54:30 -0700
From:	Scotty Bauer <sbauer@....utah.edu>
To:	linux-kernel@...r.kernel.org
Subject: Accessing user-land memory without safe functions

I Have been auditing a few drivers and have found some of them are
accessing user-land memory without either mapping the pages in, or
copying the data via the safe user access apis. 

The thing I have mostly been seeing is something along the lines of:

ioctl(etc, etc, arg) {

char buf[32];
__user *some_struct  = (type cast) arg;

size_t amount = some_struct->amount;

** do size check on amount **

copy_from_user(buf, some_struct->some_uland_addr, amount);

}

Above you see 2 unsafe user-land dereferences, the
some_struct->amount and some_struct->some_uland_addr.

Since I've seen this a couple times now I'm wondering if my
understanding of touching user-land memory is flawed.

For the above example Ioctl, the proper way to get access to those fields
through the safe copy_from_user or get_user() functions, correct?

I'm wondering if I should submit patches to fix the issues I've found,
but now I'm doubting whether they're really issues at all.

Thanks,
Scotty
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