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SubjectRe: mapping user space buffer to kernel address space


On Wed, 18 Oct 2000, Jeff Garzik wrote:
>
> Well coolio. Would somebody be up for sanity checking my audio mmap
> code (attached)? It doesn't look too hard at all to get the audio
> drivers doing the correct thing.

Looks reasonable - although your "max_size" checks are wrong at mmap time.
You should check for something like

if (size > max_size)
goto out;
if (offset > max_size - size)
goto out;
instead of your current (offset >= max_size) check. As it stands, I think
you can mmap past the end by just having size and offset < max_size, but
the _sum_ being bigger..

> Since this code works in my local tests, my two concerns at this point
> are correct vma->vm_pgoff treatment, and correct vm_flags/vm_file usage.

You should drop the

vma->vm_file = file;

as the VM layer will have done that already.

Also, the VM_LOCKED | VM_SHM thing is wrong, because it will cause
mis-calulcation of the mm->vm_locked fields, and it's also unnecessary.
Sure, it will cause the VM layer to not swap, but the no-op "swapping"
shouldn't much hurt anyway, as it's easy enough to re-populate the page
again.
So either just drop it, or make sure that the locked page count doesn't
get corrupted.

Linus

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