Re: [CHECKER] copy_*_user length bugs?

[Andreas Schwab <schwab@suse.de>]

Chris Evans <chris@scary.beasts.org> writes:

|> To justify this, consider if len were set to minus 2 billion. This will
|> pass the sanity check, and pass the value straight on to copy_to_user. The
|> copy_to_user parameter is unsigned, so this value because approximately
|> +2Gb.
|> 
|> Now, providing the malicious user passes a low user space pointer (e.g.
|> just above 0), the kernel's virtual address space wrap check will not
|> trigger because ~0 + ~2Gb does not exceed 4G. And the result is the user
|> being able to read kernel memory.

On m68k this is not a problem, since kernel and user address space are
strictly distinct, even in the kernel.  The luser will get an EFAULT
eventually.

Andreas.

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