Re: [PATCH v3] vsprintf: Prevent crash when dereferencing invalid pointers

[Andy Shevchenko]

On Tue, 2018-04-03 at 13:46 +0200, Petr Mladek wrote:
> On Mon 2018-04-02 17:15:23, Andy Shevchenko wrote:
> > On Thu, 2018-03-29 at 16:53 +0200, Petr Mladek wrote:
> > > On Fri 2018-03-16 20:19:35, Andy Shevchenko wrote:
> > > > On Thu, 2018-03-15 at 16:26 +0100, Petr Mladek wrote:
> > > > > On Thu 2018-03-15 15:09:03, Andy Shevchenko wrote:
> > > > > > I still think that printing a hex value of the error code is
> > > > > > much
> > > > > > better
> > > > > > than some odd "(efault)".
> > > > > 
> > > > > Do you mean (err:0e)? Google gives rather confusing answers
> > > > > for
> > > > > this.
> > > > 
> > > > More like "(0xHHHH)" (we have already more than 512 error code
> > > > numbers.
> > > 
> > > Hmm, I have never seen the error code in this form.
> > 
> > We have limited space to print it and error numbers currently can be
> > up
> > to 0xfff (4095). So, I have no better idea how to squeeze them while
> > thinking that "(efault)" is much harder to parse in case of error
> > pointer.
> 
> But this will not be used instead of address value. It is used in
> situations
> where we print the information that is stored at the address, for
> example,
> string, IP address, dentry name.

We have a lot of API functions which returns:
-ERR_PTR
NULL
struct foo *

There is no guarantee that one of that API won't be used as a supplier
for printf().

You can't dereference ERR_PTR value, but anything else except the actual
error value is worse than value itself...

> 
> > >  Also google gives
> > > rather confusing results when searching, for example for
> > > "(0x000E)".
> > 
> > It's not primarily for google, though yeah, people would google for
> > error messages...
> > 
> > Another question is what the format: decimal versus hex for errors.
> > Maybe just "(-DDDDD)"?
> 
> This still looks confusing and google does not help.

...then we have a last option just to print a value as a pointer
address.

-- 
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy