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Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing |
Date: |
Sun, 19 Feb 2012 18:10:02 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Fri, Feb 17, 2012 at 01:35:02PM +0100, Markus Armbruster wrote:
> "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.
Hmm. Why would anyone do this?
But I get the hint I think. So I think what I will do is,
use sscanf to validate, detect the format and tokenize input,
then strtoul to read in integers.
> > Any other issues?
>
> Yes.
>
> 1. More functional changes, e.g.
>
> * "1" is no longer rejected when funcp != NULL
I think it's a bug. Why would we want to reject it?
> Probably more. I'd be particularly wary of sscanf()'s appetite for
> space.
We pass in a pre-parsed string. How can it have spaces?
> 2. Diffstat: 1 files changed, 38 insertions(+), 43 deletions(-)
>
> Why bother?
I need to extend the functionality and manual parsing
makes it very fragile.
--
MST
- [Qemu-devel] [PATCH 0/2] pci devaddr parsing cleanups, Michael S. Tsirkin, 2012/02/16
- [Qemu-devel] [PATCH 1/2] pci: don't export an internal function, Michael S. Tsirkin, 2012/02/16
- [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, Michael S. Tsirkin, 2012/02/16
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, malc, 2012/02/16
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, Eric Blake, 2012/02/16
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, malc, 2012/02/16
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, Michael S. Tsirkin, 2012/02/17
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, Markus Armbruster, 2012/02/17
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, Michael S. Tsirkin, 2012/02/19
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, Michael S. Tsirkin, 2012/02/17
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, malc, 2012/02/17
- Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing, Michael S. Tsirkin, 2012/02/17