Re: [Qemu-devel] [PATCH for-2.11] qcow2: Fix overly broad madvise()

[Alberto Garcia]

On Tue 14 Nov 2017 07:41:27 PM CET, Max Reitz wrote:
> @mem_size and @offset are both size_t, thus subtracting them from one
> another will just return a big size_t if mem_size < offset -- even more
> obvious here because the result is stored in another size_t.
>
> Checking that result to be positive is therefore not sufficient to
> excluse the case that offset > mem_size.  Thus, we currently sometimes
> issue an madvise() over a very large address range.
>
> This is triggered by iotest 163, but with -m64, this does not result in
> tangible problems.  But with -m32, this test produces three segfaults,
> all of which are fixed by this patch.
>
> Signed-off-by: Max Reitz <address@hidden>

Oh, I guess this happens when the page size is larger than the cluster
size? Otherwise I don't see how...

Reviewed-by: Alberto Garcia <address@hidden>

Berto