Re: [Qemu-devel] [PATCH] usb: fix serial generator

[Eric Blake]

On 10/05/2016 04:33 AM, Gerd Hoffmann wrote:
> snprintf return value is *not* the number of chars written into the
> buffer, but the number of chars needed.  So in case the buffer is too
> small you can go alloc a bigger one and try again.  But that also means
> you can't simply use the return value for the next snprintf call
> without checking beforehand that things did actually fit.
> 
> Problem is that usb_desc_create_serial didn't perform that check, so a
> loooong path string (can happen with deep pci-bridge nesting) results in
> the third snprintf call smashing the stack.

Is this exploitable enough to need a CVE?

> 
> Fix this by throwing out all the snpintf calls and use g_strdup_printf

s/snpintf/snprintf/

> instead.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1381630
> 
> Reported-by: Thomas Huth <address@hidden>
> Signed-off-by: Gerd Hoffmann <address@hidden>
> ---
>  hw/usb/desc.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)

Reviewed-by: Eric Blake <address@hidden>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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