[PATCH net] ethtool: rss: Fix hfunc and input_xfrm parsing on big endian

[Gal Pressman <gal@nvidia.com>]

ETHTOOL_A_RSS_HFUNC and ETHTOOL_A_RSS_INPUT_XFRM are NLA_U32 attributes,
but ethnl_rss_set() and ethnl_rss_create_doit() parse them with
ethnl_update_u8(), which reads a single byte.

On little endian this happens to read the least significant byte and
works as long as the value fits in a byte. On big endian it reads the
most significant byte, so the requested value is parsed incorrectly.

The destination fields in struct ethtool_rxfh_param are u8, so the
attribute can't be read directly with ethnl_update_u32().
Cap the hfunc policy at U8_MAX so an out of range value is rejected
instead of being silently truncated into the u8 field, and add
ethnl_update_u8_u32() to read the full u32 and narrow it into the u8
destination.

Fixes: 82ae67cbc423 ("ethtool: rss: support setting hfunc via Netlink")
Fixes: d3e2c7bab124 ("ethtool: rss: support setting input-xfrm via Netlink")
Fixes: a166ab7816c5 ("ethtool: rss: support creating contexts via Netlink")
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
---
 net/ethtool/netlink.h | 28 ++++++++++++++++++++++++++++
 net/ethtool/rss.c     | 14 ++++++++------
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
index fd2198e45d2b..733fb3c3a63a 100644
--- a/net/ethtool/netlink.h
+++ b/net/ethtool/netlink.h
@@ -115,6 +115,34 @@ static inline void ethnl_update_u8(u8 *dst, const struct nlattr *attr,
 	*mod = true;
 }
 
+/**
+ * ethnl_update_u8_u32() - update u8 value from an NLA_U32 attribute
+ * @dst:  value to update
+ * @attr: netlink attribute with new value or null
+ * @mod:  pointer to bool for modification tracking
+ *
+ * Some attributes are NLA_U32 on the wire but are stored in a u8. Read the
+ * full 32-bit value from NLA_U32 netlink attribute @attr and narrow it into
+ * the u8 pointed to by @dst; do nothing if @attr is null.
+ * Bool pointed to by @mod is set to true if this function changed the value
+ * of *dst, otherwise it is left as is.
+ */
+static inline void ethnl_update_u8_u32(u8 *dst, const struct nlattr *attr,
+				       bool *mod)
+{
+	u32 val;
+
+	if (!attr)
+		return;
+	val = nla_get_u32(attr);
+	DEBUG_NET_WARN_ON_ONCE(val > U8_MAX);
+	if (*dst == val)
+		return;
+
+	*dst = val;
+	*mod = true;
+}
+
 /**
  * ethnl_update_bool32() - update u32 used as bool from NLA_U8 attribute
  * @dst:  value to update
diff --git a/net/ethtool/rss.c b/net/ethtool/rss.c
index 53792f53f922..ca6ed152c2be 100644
--- a/net/ethtool/rss.c
+++ b/net/ethtool/rss.c
@@ -574,7 +574,7 @@ static const struct nla_policy ethnl_rss_flows_policy[] = {
 const struct nla_policy ethnl_rss_set_policy[ETHTOOL_A_RSS_FLOW_HASH + 1] = {
 	[ETHTOOL_A_RSS_HEADER] = NLA_POLICY_NESTED(ethnl_header_policy),
 	[ETHTOOL_A_RSS_CONTEXT] = { .type = NLA_U32, },
-	[ETHTOOL_A_RSS_HFUNC] = NLA_POLICY_MIN(NLA_U32, 1),
+	[ETHTOOL_A_RSS_HFUNC] = NLA_POLICY_RANGE(NLA_U32, 1, U8_MAX),
 	[ETHTOOL_A_RSS_INDIR] = { .type = NLA_BINARY, },
 	[ETHTOOL_A_RSS_HKEY] = NLA_POLICY_MIN(NLA_BINARY, 1),
 	[ETHTOOL_A_RSS_INPUT_XFRM] =
@@ -855,7 +855,7 @@ ethnl_rss_set(struct ethnl_req_info *req_info, struct genl_info *info)
 	indir_mod = !!tb[ETHTOOL_A_RSS_INDIR];
 
 	rxfh.hfunc = data.hfunc;
-	ethnl_update_u8(&rxfh.hfunc, tb[ETHTOOL_A_RSS_HFUNC], &mod);
+	ethnl_update_u8_u32(&rxfh.hfunc, tb[ETHTOOL_A_RSS_HFUNC], &mod);
 	if (rxfh.hfunc == data.hfunc)
 		rxfh.hfunc = ETH_RSS_HASH_NO_CHANGE;
 
@@ -864,7 +864,8 @@ ethnl_rss_set(struct ethnl_req_info *req_info, struct genl_info *info)
 		goto exit_free_indir;
 
 	rxfh.input_xfrm = data.input_xfrm;
-	ethnl_update_u8(&rxfh.input_xfrm, tb[ETHTOOL_A_RSS_INPUT_XFRM], &mod);
+	ethnl_update_u8_u32(&rxfh.input_xfrm, tb[ETHTOOL_A_RSS_INPUT_XFRM],
+			    &mod);
 	xfrm_sym = rxfh.input_xfrm || data.input_xfrm;
 	if (rxfh.input_xfrm == data.input_xfrm)
 		rxfh.input_xfrm = RXH_XFRM_NO_CHANGE;
@@ -938,7 +939,7 @@ const struct ethnl_request_ops ethnl_rss_request_ops = {
 const struct nla_policy ethnl_rss_create_policy[ETHTOOL_A_RSS_INPUT_XFRM + 1] = {
 	[ETHTOOL_A_RSS_HEADER]	= NLA_POLICY_NESTED(ethnl_header_policy),
 	[ETHTOOL_A_RSS_CONTEXT]	= NLA_POLICY_MIN(NLA_U32, 1),
-	[ETHTOOL_A_RSS_HFUNC]	= NLA_POLICY_MIN(NLA_U32, 1),
+	[ETHTOOL_A_RSS_HFUNC]	= NLA_POLICY_RANGE(NLA_U32, 1, U8_MAX),
 	[ETHTOOL_A_RSS_INDIR]	= NLA_POLICY_MIN(NLA_BINARY, 1),
 	[ETHTOOL_A_RSS_HKEY]	= NLA_POLICY_MIN(NLA_BINARY, 1),
 	[ETHTOOL_A_RSS_INPUT_XFRM] =
@@ -1054,14 +1055,15 @@ int ethnl_rss_create_doit(struct sk_buff *skb, struct genl_info *info)
 		goto exit_clean_data;
 	indir_user_size = ret;
 
-	ethnl_update_u8(&rxfh.hfunc, tb[ETHTOOL_A_RSS_HFUNC], &mod);
+	ethnl_update_u8_u32(&rxfh.hfunc, tb[ETHTOOL_A_RSS_HFUNC], &mod);
 
 	ret = rss_set_prep_hkey(dev, info, &data, &rxfh, &mod);
 	if (ret)
 		goto exit_free_indir;
 
 	rxfh.input_xfrm = RXH_XFRM_NO_CHANGE;
-	ethnl_update_u8(&rxfh.input_xfrm, tb[ETHTOOL_A_RSS_INPUT_XFRM], &mod);
+	ethnl_update_u8_u32(&rxfh.input_xfrm, tb[ETHTOOL_A_RSS_INPUT_XFRM],
+			    &mod);
 
 	ctx = ethtool_rxfh_ctx_alloc(ops, data.indir_size, data.hkey_size);
 	if (!ctx) {
-- 
2.54.0