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Message-ID: <ZoVGqJVBWUVNtsrc@shredder.lan>
Date: Wed, 3 Jul 2024 15:40:08 +0300
From: Ido Schimmel <idosch@...dia.com>
To: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Cc: Petr Machata <petrm@...dia.com>, mlxsw@...dia.com,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/3] mlxsw: Warn about invalid accesses to array
fields
On Tue, Jul 02, 2024 at 09:08:17AM +0200, Przemek Kitszel wrote:
> On 7/1/24 18:41, Petr Machata wrote:
> > A forgotten or buggy variable initialization can cause out-of-bounds access
> > to a register or other item array field. For an overflow, such access would
> > mangle adjacent parts of the register payload. For an underflow, due to all
> > variables being unsigned, the access would likely trample unrelated memory.
> > Since neither is correct, replace these accesses with accesses at the index
> > of 0, and warn about the issue.
>
> That is not correct either, but indeed better.
>
> >
> > Suggested-by: Ido Schimmel <idosch@...dia.com>
> > Signed-off-by: Petr Machata <petrm@...dia.com>
> > Reviewed-by: Ido Schimmel <idosch@...dia.com>
> > ---
> > drivers/net/ethernet/mellanox/mlxsw/item.h | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlxsw/item.h b/drivers/net/ethernet/mellanox/mlxsw/item.h
> > index cfafbeb42586..9f7133735760 100644
> > --- a/drivers/net/ethernet/mellanox/mlxsw/item.h
> > +++ b/drivers/net/ethernet/mellanox/mlxsw/item.h
> > @@ -218,6 +218,8 @@ __mlxsw_item_bit_array_offset(const struct mlxsw_item *item,
> > }
> > max_index = (item->size.bytes << 3) / item->element_size - 1;
> > + if (WARN_ON(index > max_index))
> > + index = 0;
>
> you have BUG*() calls just above those lines :(
> anyway, WARN_ON_ONCE(), and perhaps you need to print some additional
> data to finally fix this?
The trace should be enough, but more info can be added:
diff --git a/drivers/net/ethernet/mellanox/mlxsw/item.h b/drivers/net/ethernet/mellanox/mlxsw/item.h
index 9f7133735760..a619a0736bd1 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/item.h
+++ b/drivers/net/ethernet/mellanox/mlxsw/item.h
@@ -218,7 +218,9 @@ __mlxsw_item_bit_array_offset(const struct mlxsw_item *item,
}
max_index = (item->size.bytes << 3) / item->element_size - 1;
- if (WARN_ON(index > max_index))
+ if (WARN_ONCE(index > max_index,
+ "name=%s,index=%u,max_index=%u\n", item->name, index,
+ max_index))
index = 0;
be_index = max_index - index;
offset = be_index * item->element_size >> 3;
Will leave it to Petr to decide what he wants to include there.
>
> > be_index = max_index - index;
> > offset = be_index * item->element_size >> 3;
> > in_byte_index = index % (BITS_PER_BYTE / item->element_size);
>
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