netdev - [PATCH net-next v2 1/3] mlxsw: Warn about invalid accesses to array fields

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Message-ID: <b988fb265c2f6c1206fe12d5bfdcfa188b7672d1.1720447210.git.petrm@nvidia.com>
Date: Mon, 8 Jul 2024 16:23:40 +0200
From: Petr Machata <petrm@...dia.com>
To: "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>
CC: Petr Machata <petrm@...dia.com>, Ido Schimmel <idosch@...dia.com>,
	<mlxsw@...dia.com>
Subject: [PATCH net-next v2 1/3] mlxsw: Warn about invalid accesses to array fields

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.

Suggested-by: Ido Schimmel <idosch@...dia.com>
Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---

Notes:
    v2:
    - changed to WARN_ONCE() with some prints

 drivers/net/ethernet/mellanox/mlxsw/item.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/item.h b/drivers/net/ethernet/mellanox/mlxsw/item.h
index cfafbeb42586..a619a0736bd1 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/item.h
+++ b/drivers/net/ethernet/mellanox/mlxsw/item.h
@@ -218,6 +218,10 @@ __mlxsw_item_bit_array_offset(const struct mlxsw_item *item,
 	}
 
 	max_index = (item->size.bytes << 3) / item->element_size - 1;
+	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;
 	in_byte_index  = index % (BITS_PER_BYTE / item->element_size);
-- 
2.45.0