Re: [PATCH 0/3] cmd: setexpr: add fmt format string operation

[Wolfgang Denk <wd@denx.de>]

Dear Roland,

In message <a463f32f-8ef0-6973-f1c3-a881ee6e5d26@weidmueller.com> you wrote:
>
> > These are two pretty unfortunate restrictions.  I guess it should
> > not be too hard to avoid both of these.  Can you please give it a
> > try?
>
> I think it is possible to allow more than one format parameter or more
> types. But it would make checking much more difficult.

Maybe we need _less_ checking, not more - and maybe the needed
checking is already done in the *printf() code?

> I think just passing the format string directly to sprintf should be
> avoided because it is unsafe. For example
>
> => setexpr foo fmt %s 0xffffffff
>
> would surely lead to access on memory location outside the variable
> where 0xffffffff is stored.

Only if you make the wrong assumptions.  I would expect this to
result in

	foo=0xffffffff

in the same way as the bash builting gives

	$ printf '%s\n' 0xffffffff
	0xffffffff

> > => setexpr foo fmt "%0x08x-%s-%d-%s" $a $b $c $d
>
> I think the only way to support such expressions in a save way would
> be implementing an own format string parser for setexpr with

Maybe it makes sense to have a look at the bash code?

Best regards,

Wolfgang Denk

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