[PATCH] drm/amdgpu: Handle potential NULL pointer dereference

[Yazen Ghannam]

On Thu, Aug 25, 2022 at 08:54:46AM -0400, Russell, Kent wrote:
> [AMD Official Use Only - General]
> 
> It does indeed short-circuit on || (If the left side of an || statement is not 0, it doesn't evaluate the right side and returns true). So we can ignore this patch, since checking for each individual field on the 2nd term is probably overkill. We were still investigating what got passed in and why it wasn't valid, so I'll drop this for now. Thanks Lijo!

Right, the "||" will short-circuit, but not the "&&".

...

> > +	if (!m)
> > +		return NOTIFY_DONE;
> > +
> >   	/*
> >   	 * If the error was generated in UMC_V2, which belongs to GPU UMCs,
> >   	 * and error occurred in DramECC (Extended error code = 0) then only
> >   	 * process the error, else bail out.
> >   	 */
> > -	if (!m || !((smca_get_bank_type(m->extcpu, m->bank) == SMCA_UMC_V2) &&
> > +	if (!((smca_get_bank_type(m->extcpu, m->bank) == SMCA_UMC_V2) &&
> >   		    (XEC(m->status, 0x3f) == 0x0)))

If m is NULL, then we get (!m || "Don't care") = true. We avoid the second
operand.

But then we have (true && "Something with 'm->' in it"). The second operand in
the && needs to be checked, and this will cause a NULL pointer dereference if
m is NULL.

What do you guys think?

Thanks,
Yazen