Re: [Xen-devel] [PATCH] vsprintf: Make sure argument to %*ph/%pv is valid

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 02/10/2015 04:49 PM, Andrew Cooper wrote:
> On 10/02/2015 21:44, Boris Ostrovsky wrote:
> > If NULL pointer is passed for these specifiers then print '-'
> > or 'd-v-'.
> >
> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Instead of special casing each custom format, I would be tempted just to
> put the switch() in an if(arg) conditional, and fall back to the regular
> number for a NULL pointer, or go along the glibc route and print "(NULL)".
OK, I could do that.

> I presume you found this by falling over a NULL  pointer while
> debugging?  I can't see a legitimate reason for formally supporting NULL
> pointers in each context, but crashing is certainly better avoided.
Yes, I hit %pv case when the vcpu I was tracking turned NULL. And yes, 
we then crash.
-boris

> ~Andrew
>
> > ---
> >   xen/common/vsprintf.c |   19 +++++++++++++++++++
> >   1 files changed, 19 insertions(+), 0 deletions(-)
> >
> > diff --git a/xen/common/vsprintf.c b/xen/common/vsprintf.c
> > index 065cc42..84cfa85 100644
> > --- a/xen/common/vsprintf.c
> > +++ b/xen/common/vsprintf.c
> > @@ -280,6 +280,13 @@ static char *pointer(char *str, char *end, const char 
> > **fmt_ptr,
> >           /* Consumed 'h' from the format string. */
> >           ++*fmt_ptr;
> >   
> > +        if ( hex_buffer == NULL )
> > +        {
> > +            if ( str < end )
> > +                *str++ = '-';
> > +            return str;
> > +        }
> > +
> >           /* Bound user count from %* to between 0 and 64 bytes. */
> >           if ( field_width <= 0 )
> >               return str;
> > @@ -338,6 +345,18 @@ static char *pointer(char *str, char *end, const char 
> > **fmt_ptr,
> >           ++*fmt_ptr;
> >           if ( str < end )
> >               *str = 'd';
> > +        if ( v == NULL )
> > +        {
> > +            /* If v is NULL then print 'd-v-' */
> > +            str++;
> > +            if ( str < end )
> > +                *str++ = '-';
> > +            if ( str < end )
> > +                *str++ = 'v';
> > +            if ( str < end )
> > +                *str++ = '-';
> > +            return str;
> > +        }
> >           str = number(str + 1, end, v->domain->domain_id, 10, -1, -1, 0);
> >           if ( str < end )
> >               *str = 'v';

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