Re: [PATCH v3] qemu-sockets: fix unix socket path copy (again)

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Sep 01, 2021 at 04:16:24PM +0300, Michael Tokarev wrote:
> Commit 4cfd970ec188558daa6214f26203fe553fb1e01f added an
> assert which ensures the path within an address of a unix
> socket returned from the kernel is at least one byte and
> does not exceed sun_path buffer. Both of this constraints
> are wrong:
> 
> A unix socket can be unnamed, in this case the path is
> completely empty (not even \0)
> 
> And some implementations (notable linux) can add extra
> trailing byte (\0) _after_ the sun_path buffer if we
> passed buffer larger than it (and we do).
> 
> So remove the assertion (since it causes real-life breakage)
> but at the same time fix the usage of sun_path. Namely,
> we should not access sun_path[0] if kernel did not return
> it at all (this is the case for unnamed sockets),
> and use the returned salen when copyig actual path as an
> upper constraint for the amount of bytes to copy - this
> will ensure we wont exceed the information provided by
> the kernel, regardless whenever there is a trailing \0
> or not. This also helps with unnamed sockets.
> 
> Note the case of abstract socket, the sun_path is actually
> a blob and can contain \0 characters, - it should not be
> passed to g_strndup and the like, it should be accessed by
> memcpy-like functions.
> 
> Fixes: 4cfd970ec188558daa6214f26203fe553fb1e01f
> Fixes: http://bugs.debian.org/993145
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> CC: qemu-stable@nongnu.org
> ---
>  util/qemu-sockets.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


Regards,
Daniel
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