Re: [PATCH net 4/5] net: dsa: mv88e6xxx: bound the policy rule dump by the caller's buffer size

On Wed, Sep 02, 2026 at 08:26:10PM -0700, Jakub Kicinski wrote:

mv88e6xxx_get_rxnfc() uses rxnfc->rule_cnt as the write index while
dumping the policy IDR, clobbering the input value before it has been
looked at.  That input is the number of entries the caller had room for.
ETHTOOL_GRXCLSRLALL requires no CAP_NET_ADMIN and the ioctl sizes the
buffer from the rule_cnt userspace passes in, so once an admin has
installed policy rules any user can ask for fewer slots than there are
rules and run off the end of the allocation.  A rule_cnt of 0 leaves the
buffer pointer NULL and the walk dereferences it.

Count into a local so the caller's limit survives the walk, and stop with
-EMSGSIZE once it is reached.

Fixes: da7dc8755304 ("net: dsa: mv88e6xxx: add RXNFC support")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: andrew@lunn.ch
CC: olteanv@gmail.com
CC: vivien.didelot@gmail.com
CC: f.fainelli@gmail.com
---
 drivers/net/dsa/mv88e6xxx/chip.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

Reviewed-by: Joe Damato <redacted>