[PATCH net 1/5] net: dsa: bcm_sf2: bound the CFP rule dump by the caller's buffer size

[Jakub Kicinski <kuba@kernel.org>]

bcm_sf2_cfp_rule_get_all() walks the whole cfp.unique bitmap into
rule_locs[] without consulting nfc->rule_cnt, which is how many 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 CFP 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.

Fixes: 7318166cacad ("net: dsa: bcm_sf2: Add support for ethtool::rxnfc")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: florian.fainelli@broadcom.com
CC: jonas.gorski@gmail.com
CC: andrew@lunn.ch
CC: olteanv@gmail.com
---
 drivers/net/dsa/bcm_sf2_cfp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/dsa/bcm_sf2_cfp.c b/drivers/net/dsa/bcm_sf2_cfp.c
index 50d3a818eb1b..84a086c3e99b 100644
--- a/drivers/net/dsa/bcm_sf2_cfp.c
+++ b/drivers/net/dsa/bcm_sf2_cfp.c
@@ -1088,6 +1088,8 @@ static int bcm_sf2_cfp_rule_get_all(struct bcm_sf2_priv *priv,
 	unsigned int index = 1, rules_cnt = 0;
 
 	for_each_set_bit_from(index, priv->cfp.unique, priv->num_cfp_rules) {
+		if (rules_cnt == nfc->rule_cnt)
+			return -EMSGSIZE;
 		rule_locs[rules_cnt] = index;
 		rules_cnt++;
 	}
-- 
2.55.0