Re: [PATCH][RESEND] Fix a potential NULL pointer deref in the aic7xxx,ahc_print_register() function

[Justin T. Gibbs]

All of this logic was simplified back in '05 in the BSD drivers by adding
this to the top of the function:

       u_int   dummy_column;
 
       if (cur_column == NULL) {
               dummy_column = 0;
               cur_column = &dummy_column;
       }

and then stripping out the cur_column == NULL checks in the routine.

--
Justin

Jesper Juhl wrote:
> On 04/08/07, James Bottomley <James.Bottomley@xxxxxxxxxxxx> wrote:
> > On Sat, 2007-08-04 at 20:30 +0200, Jesper Juhl wrote:
> > > (resend of patch previously submitted on 28-Jul-2007 23:06)
> > >
> > >
> > > Ehlo,
> > >
> > > The Coverity checker noticed that we have a potential NULL pointer
> > > deref in drivers/scsi/aic7xxx/aic7xxx_core.c::ahc_print_register().
> > > This patch handles it by adding the same test against NULL that is
> > > used elsewhere in the same function.
> > It's on my list of things to look at ... but not very high.  I suspect
> > it actually isn't triggerable, but if you can tell me how, it will save
> > me from looking.
>
> Here's what Coverity reported :
> ...
> 6525 	int
> 6526 	ahc_print_register(ahc_reg_parse_entry_t *table, u_int num_entries,
> 6527 			   const char *name, u_int address, u_int value,
> 6528 			   u_int *cur_column, u_int wrap_point)
> 6529 	{
> 6530 		int	printed;
> 6531 		u_int	printed_mask;
> 6532 	
>
> Event var_compare_op: Added "cur_column" due to comparison "cur_column != 0"
> Also see events: [var_deref_op]
> At conditional (1): "cur_column != 0" taking false path
>
> 6533 		if (cur_column != NULL && *cur_column >= wrap_point) {
> 6534 			printf("\n");
> 6535 			*cur_column = 0;
> 6536 		}
> 6537 		printed = printf("%s[0x%x]", name, value);
>
> At conditional (2): "table == 0" taking true path
>
> 6538 		if (table == NULL) {
> 6539 			printed += printf(" ");
>
> Event var_deref_op: Variable "cur_column" tracked as NULL was dereferenced.
> Also see events: [var_compare_op]
>
> 6540 			*cur_column += printed;
> 6541 			return (printed);
> 6542 		}
> ...
>
> So it requires a NULL 'table' and a != NULL 'cur_column' to trigger.
> Whether or not that's actually possible I'm not sure, but it seems
> safer to guard against it :)
>
>
> By the way; if this can actually be triggered, then
> ahd_print_register() has the same problem.
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