Re: [PATCH bpf] bpf: Fix offset calculation error in __copy_map_value and zero_map_value

[Xu Kuohai]

On 11/12/2022 4:45 AM, Kumar Kartikeya Dwivedi wrote:
> On Sat, Nov 12, 2022 at 12:47:52AM IST, sdf@xxxxxxxxxx wrote:
> > On 11/11, Xu Kuohai wrote:
> > > From: Xu Kuohai <xukuohai@xxxxxxxxxx>
> >
> > > Function __copy_map_value and zero_map_value miscalculated copy offset,
> > > resulting in possible copy of unwanted data to user or kernel.
> >
> > > Fix it.
> >
> > > Fixes: cc48755808c6 ("bpf: Add zero_map_value to zero map value with
> > > special fields")
> > > Fixes: 4d7d7f69f4b1 ("bpf: Adapt copy_map_value for multiple offset case")
> > > Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
> > > ---
> > >    include/linux/bpf.h | 4 ++--
> > >    1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 74c6f449d81e..c1bd1bd10506 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -315,7 +315,7 @@ static inline void __copy_map_value(struct bpf_map
> > > *map, void *dst, void *src, b
> > >    		u32 next_off = map->off_arr->field_off[i];
> >
> > >    		memcpy(dst + curr_off, src + curr_off, next_off - curr_off);
> > > -		curr_off += map->off_arr->field_sz[i];
> > > +		curr_off = next_off + map->off_arr->field_sz[i];
> > >    	}
> > >    	memcpy(dst + curr_off, src + curr_off, map->value_size - curr_off);
> > >    }
> > > @@ -344,7 +344,7 @@ static inline void zero_map_value(struct bpf_map
> > > *map, void *dst)
> > >    		u32 next_off = map->off_arr->field_off[i];
> >
> > >    		memset(dst + curr_off, 0, next_off - curr_off);
> > > -		curr_off += map->off_arr->field_sz[i];
> > > +		curr_off = next_off + map->off_arr->field_sz[i];
> > >    	}
> > >    	memset(dst + curr_off, 0, map->value_size - curr_off);
> > >    }
> >
> > Hmm, does it mean that it currently works only for the cases where
> > these special fields are first/last?
> >
> > Also, what about bpf-next? The same problem seem to exist there?
>
> Replied with the patch in the other email.
>
> > Might be a good idea to have some selftest to exercise this?
>
> I agree, there was another bug in the same code before this, so I think we
> should add tests for this (I should have done that with the commit being
> fixed...).
>
> Xu, if you have cycles, can you work on testing a few edge cases and make sure
> we don't regress in the future? Otherwise I will take a look next week.
> .

Ok, I'll add a few cases to test_sk_storage_map to capture this