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

[Markus Armbruster]

"Michael S. Tsirkin" <address@hidden> writes:

> On Thu, Feb 16, 2012 at 01:39:02PM -0700, Eric Blake wrote:
>> 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.
>
> Seems easy to fix: I'll just set maximum field width of 8.

Nope.  Functional change: "000000001.2" is no longer accepted.

> Any other issues?

Yes.

1. More functional changes, e.g.

   * "1" is no longer rejected when funcp != NULL

   Probably more.  I'd be particularly wary of sscanf()'s appetite for
   space.

2. Diffstat: 1 files changed, 38 insertions(+), 43 deletions(-)

Why bother?