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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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)".

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.

~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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