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Re: [Qemu-block] [PATCH 2/2] iov: assert that qiov->size doesn't exceed


From: Max Reitz
Subject: Re: [Qemu-block] [PATCH 2/2] iov: assert that qiov->size doesn't exceed INT_MAX
Date: Wed, 1 Feb 2017 22:51:01 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 31.01.2017 17:09, Alberto Garcia wrote:
> The type of qiov->size is size_t but the QEMU I/O code uses int all
> over the place to measure request sizes. Overflows are likely going
> to be detected by any of the many assert(qiov->size == nbytes), where
> nbytes is an int, but let's add proper checks in the QEMUIOVector
> initialization, which is where it belongs.

I'm not entirely convinced that's where it belongs. In my opinion, the
BlockBackend functions should all get uint64_t size parameters and let
blk_check_byte_request() do the rest.

I wouldn't mind too much if blk_check_byte_requests() did assertions
instead of returning -EIO.

But the thing with the I/O vector is that it's not exclusively used for
the block layer. I can see at least hw/9pfs/9p.c and hw/usb/core.c using
it internally.

The assertion probably makes sense even for them, considering that
size_t does not have a constant size. But I'm not entirely sold that the
I/O vector creation is actually the place where the assertions belong.

Max

> 
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  util/iov.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/util/iov.c b/util/iov.c
> index 74e6ca8ed7..6b5cc9203c 100644
> --- a/util/iov.c
> +++ b/util/iov.c
> @@ -283,13 +283,18 @@ void qemu_iovec_init_external(QEMUIOVector *qiov, 
> struct iovec *iov, int niov)
>      qiov->niov = niov;
>      qiov->nalloc = -1;
>      qiov->size = 0;
> -    for (i = 0; i < niov; i++)
> +    for (i = 0; i < niov; i++) {
> +        assert(iov[i].iov_len <= INT_MAX);
> +        assert(qiov->size <= INT_MAX - iov[i].iov_len);
>          qiov->size += iov[i].iov_len;
> +    }
>  }
>  
>  void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len)
>  {
>      assert(qiov->nalloc != -1);
> +    assert(len <= INT_MAX);
> +    assert(qiov->size <= INT_MAX - len);
>  
>      if (qiov->niov == qiov->nalloc) {
>          qiov->nalloc = 2 * qiov->nalloc + 1;
> 


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