Re: [RFC PATCH 1/2] lib, stackdepot: check stackdepot handle before accessing slabs.

[imran . f . khan]

On 1/9/21 6:58 pm, Vlastimil Babka wrote:
> +CC linux-mm, Alex
>
> On 9/1/21 07:19, Imran Khan wrote:
> > stack_depot_save allocates slabs that will be used for storing
> > objects in future.If this slab allocation fails we may get to
> > a situation where space allocation for a new stack_record fails,
> > causing stack_depot_save to return 0 as handle.
> > If user of this handle ends up invoking stack_depot_fetch with
> > this handle value, current implementation of stack_depot_fetch
> > will end up using slab from wrong index.
> > To avoid this check handle value at the beginning.
> > Also issue a warning for nil handle values and when slab allocation
> > for stackdepot fails for the first time.
> >
> > Signed-off-by: Imran Khan <imran.f.khan@xxxxxxxxxx>
> > Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
>
> Agree but without the warnings please, especially the "stack depot handle is
> absent" one. It's just something that can happen e.g. in GFP_NOWAIT contexts
> and no need to spam dmesg.

Okay. I have removed warnings in v2 of patch set.

> > ---
> >   lib/stackdepot.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> > index 0a2e417f83cb..1d42ef9ef766 100644
> > --- a/lib/stackdepot.c
> > +++ b/lib/stackdepot.c
> > @@ -232,6 +232,10 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
> >   	struct stack_record *stack;
> >   
> >   	*entries = NULL;
> > +	if (!handle) {
> > +		WARN(1, "stack depot handle is absent.\n");
> > +		return 0;
> > +	}
> >   	if (parts.slabindex > depot_index) {
> >   		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
> >   			parts.slabindex, depot_index, handle);
> > @@ -303,6 +307,8 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
> >   		page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
> >   		if (page)
> >   			prealloc = page_address(page);
> > +		else
> > +			WARN_ONCE(1, "slab allocation for stack depot failed.\n");
> >   	}
> >   
> >   	raw_spin_lock_irqsave(&depot_lock, flags);
Thanks for reviewing this.

--Imran