Re: kprobe_handler should check pre_handler function

[William Cohen <wcohen@redhat.com>]

Ananth N Mavinakayanahalli wrote:
> On Mon, Mar 28, 2005 at 04:10:32PM -0500, William Cohen wrote:
> 
> Hi Will,
> 
> 
>>I found kprobes expects there to be a pre_handler function in the 
>>structure. I was writing a probe that only needed a post_handler 
>>function, no pre_handler function. The probe was tracking the 
>>destinations of indirect calls and jumps, the probe needs to fire after 
>>the instruction single steps to get the target address. The probe 
>>crashed the machine because arch/i386/kernel/kprobe.c:kprobe_handler() 
>>blindly calls p->pre_handler().  There should be a check to verify that 
>>the pointer is non-null. There are cases where the pre_handler is not 
>>needed and it would make sense to set it to NULL. Thus, a check should 
>>be done for pre_handler like post_handler and fault_handler.
> 
> 
> You are right. The check for pre_handler is needed and here is a patch
> against 2.6.12-rc1-mm3 that does this.
> 
> Thanks,
> Ananth

Ananth,

Thanks. It looks like it addresses the problem. Could you see about 
getting this patch in the upstream kernel?

-Will