Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing

[Eric Blake <eblake@redhat.com>]

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On 02/16/2012 12:23 PM, malc wrote:
> On Thu, 16 Feb 2012, Michael S. Tsirkin wrote:
> 
>> Use scanf instead of manual string scanning.
>>
>> +
>> +    /* Parse [[<domain>:]<bus>:]<slot> */
>> +    sscanf(addr, "%x:%x:%x%n", &dom, &bus, &slot, &n);
> 
> sscanf can fail.

Worse, the *scanf family has undefined behavior on integer overflow.  If
addr contains "100000000000000:0:0", there's no telling whether it will
be diagnosed as a parse error, or silently accepted and truncated, in
which case, there's no telling what dom will contain.

I cringe any time I see someone using scanf to parse numbers from
arbitrary user input; I barely tolerate it for parsing things generated
by the kernel, but even there, I won't ever use scanf myself.  Same goes
for atoi.  _Only_ strtol and friends can robustly parse arbitrary input
into integers.

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


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