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

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH for-2.11] qcow2: Fix overly broad madvise()
Date: Tue, 14 Nov 2017 13:51:36 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 11/14/2017 12:41 PM, 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>
> ---
>  block/qcow2-cache.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Eric Blake <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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