[PATCH net 2/5] eth: nfp: bound the ntuple rule dump by the caller's buffer size

nfp_net_get_fs_loc() dumps every entry of nn->fs.list into rule_locs[]
without consulting cmd->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 flow steering 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.

Bail out with -EMSGSIZE when the buffer fills up, the way the other
ntuple capable drivers do, and report how many locations were filled so
a shrinking rule list does not leave the caller reading stale slots.

Reported-by: VEGA <redacted>
Fixes: 9eb03bb1c035 ("nfp: add ethtool flow steering callbacks")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: leitao@debian.org
CC: louis.peens@corigine.com
CC: yinjun.zhang@corigine.com
CC: oss-drivers@corigine.com
---
 drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c b/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c
index a2a89d48e3ca..9419e1ed8466 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c

@@ -1421,7 +1421,8 @@ static int nfp_net_get_fs_rule(struct nfp_net *nn, struct ethtool_rxnfc *cmd)
 	return -ENOENT;
 }
 
-static int nfp_net_get_fs_loc(struct nfp_net *nn, u32 *rule_locs)
+static int nfp_net_get_fs_loc(struct nfp_net *nn, struct ethtool_rxnfc *cmd,
+			      u32 *rule_locs)
 {
 	struct nfp_fs_entry *entry;
 	u32 count = 0;

@@ -1429,8 +1430,12 @@ static int nfp_net_get_fs_loc(struct nfp_net *nn, u32 *rule_locs)
 	if (!(nn->cap_w1 & NFP_NET_CFG_CTRL_FLOW_STEER))
 		return -EOPNOTSUPP;
 
-	list_for_each_entry(entry, &nn->fs.list, node)
+	list_for_each_entry(entry, &nn->fs.list, node) {
+		if (count == cmd->rule_cnt)
+			return -EMSGSIZE;
 		rule_locs[count++] = entry->loc;
+	}
+	cmd->rule_cnt = count;
 
 	return 0;
 }

@@ -1455,7 +1460,7 @@ static int nfp_net_get_rxnfc(struct net_device *netdev,
 		return nfp_net_get_fs_rule(nn, cmd);
 	case ETHTOOL_GRXCLSRLALL:
 		cmd->data = NFP_FS_MAX_ENTRY;
-		return nfp_net_get_fs_loc(nn, rule_locs);
+		return nfp_net_get_fs_loc(nn, cmd, rule_locs);
 	default:
 		return -EOPNOTSUPP;
 	}

-- 
2.55.0