Date:   Tue, 2 Jul 2019 15:05:15 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        John Linville <linville@...driver.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Johannes Berg <johannes@...solutions.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 05/15] ethtool: helper functions for netlink
 interface

Tue, Jul 02, 2019 at 01:50:04PM CEST, mkubecek@...e.cz wrote:
>Add common request/reply header definition and helpers to parse request
>header and fill reply header. Provide ethnl_update_* helpers to update
>structure members from request attributes (to be used for *_SET requests).
>
>Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
>---
> include/uapi/linux/ethtool_netlink.h |  23 ++++
> net/ethtool/netlink.c                | 173 +++++++++++++++++++++++++++
> net/ethtool/netlink.h                | 145 ++++++++++++++++++++++
> 3 files changed, 341 insertions(+)
>
>diff --git a/include/uapi/linux/ethtool_netlink.h b/include/uapi/linux/ethtool_netlink.h
>index 9a0fbd4f85d9..ffd7db0848ef 100644
>--- a/include/uapi/linux/ethtool_netlink.h
>+++ b/include/uapi/linux/ethtool_netlink.h
>@@ -29,6 +29,29 @@ enum {
> 	ETHTOOL_MSG_KERNEL_MAX = (__ETHTOOL_MSG_KERNEL_CNT - 1)
> };
> 
>+/* request header */
>+
>+/* use compact bitsets in reply */
>+#define ETHTOOL_RF_COMPACT		(1 << 0)

"COMPACT_BITSETS"?


>+/* provide optional reply for SET or ACT requests */
>+#define ETHTOOL_RF_REPLY		(1 << 1)

"OPTIONAL_REPLY"?


>+
>+#define ETHTOOL_RF_ALL (ETHTOOL_RF_COMPACT | \
>+			ETHTOOL_RF_REPLY)
>+
>+enum {
>+	ETHTOOL_A_HEADER_UNSPEC,
>+	ETHTOOL_A_HEADER_DEV_INDEX,		/* u32 */
>+	ETHTOOL_A_HEADER_DEV_NAME,		/* string */
>+	ETHTOOL_A_HEADER_INFOMASK,		/* u32 */
>+	ETHTOOL_A_HEADER_GFLAGS,		/* u32 - ETHTOOL_RF_* */
>+	ETHTOOL_A_HEADER_RFLAGS,		/* u32 */
>+
>+	/* add new constants above here */
>+	__ETHTOOL_A_HEADER_CNT,
>+	ETHTOOL_A_HEADER_MAX = (__ETHTOOL_A_HEADER_CNT - 1)
>+};
>+
> /* generic netlink info */
> #define ETHTOOL_GENL_NAME "ethtool"
> #define ETHTOOL_GENL_VERSION 1
>diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
>index 3c98b41f04e5..e13f29bbd625 100644
>--- a/net/ethtool/netlink.c
>+++ b/net/ethtool/netlink.c
>@@ -1,8 +1,181 @@
> // SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
> 
>+#include <net/sock.h>
> #include <linux/ethtool_netlink.h>
> #include "netlink.h"
> 
>+static struct genl_family ethtool_genl_family;
>+
>+static const struct nla_policy dflt_header_policy[ETHTOOL_A_HEADER_MAX + 1] = {
>+	[ETHTOOL_A_HEADER_UNSPEC]	= { .type = NLA_REJECT },
>+	[ETHTOOL_A_HEADER_DEV_INDEX]	= { .type = NLA_U32 },
>+	[ETHTOOL_A_HEADER_DEV_NAME]	= { .type = NLA_NUL_STRING,
>+					    .len = IFNAMSIZ - 1 },
>+	[ETHTOOL_A_HEADER_INFOMASK]	= { .type = NLA_U32 },
>+	[ETHTOOL_A_HEADER_GFLAGS]	= { .type = NLA_U32 },
>+	[ETHTOOL_A_HEADER_RFLAGS]	= { .type = NLA_U32 },
>+};
>+
>+/**
>+ * ethnl_parse_header() - parse request header
>+ * @req_info:    structure to put results into
>+ * @nest:        nest attribute with request header
>+ * @net:         request netns
>+ * @extack:      netlink extack for error reporting
>+ * @policy:      netlink attribute policy to validate header; use
>+ *               @dflt_header_policy (all attributes allowed) if null
>+ * @require_dev: fail if no device identiified in header
>+ *
>+ * Parse request header in nested attribute @nest and puts results into
>+ * the structure pointed to by @req_info. Extack from @info is used for error
>+ * reporting. If req_info->dev is not null on return, reference to it has
>+ * been taken. If error is returned, *req_info is null initialized and no
>+ * reference is held.
>+ *
>+ * Return: 0 on success or negative error code
>+ */
>+int ethnl_parse_header(struct ethnl_req_info *req_info,
>+		       const struct nlattr *nest, struct net *net,

s/nest/header/ ? Nest is way too generic and really tells nothing :/


>+		       struct netlink_ext_ack *extack,
>+		       const struct nla_policy *policy, bool require_dev)
>+{
>+	struct nlattr *tb[ETHTOOL_A_HEADER_MAX + 1];
>+	const struct nlattr *devname_attr;
>+	struct net_device *dev = NULL;
>+	int ret;
>+
>+	if (!nest) {
>+		NL_SET_ERR_MSG(extack, "request header missing");
>+		return -EINVAL;
>+	}
>+	ret = nla_parse_nested(tb, ETHTOOL_A_HEADER_MAX, nest,
>+			       policy ?: dflt_header_policy, extack);
>+	if (ret < 0)

if (ret)

Same remark goes to the rest of the code (also the rest of the patches),
in case called function cannot return positive values.


>+		return ret;
>+	devname_attr = tb[ETHTOOL_A_HEADER_DEV_NAME];
>+
>+	if (tb[ETHTOOL_A_HEADER_DEV_INDEX]) {
>+		u32 ifindex = nla_get_u32(tb[ETHTOOL_A_HEADER_DEV_INDEX]);
>+
>+		dev = dev_get_by_index(net, ifindex);
>+		if (!dev) {
>+			NL_SET_ERR_MSG_ATTR(extack,
>+					    tb[ETHTOOL_A_HEADER_DEV_INDEX],
>+					    "no device matches ifindex");
>+			return -ENODEV;
>+		}
>+		/* if both ifindex and ifname are passed, they must match */
>+		if (devname_attr &&
>+		    strncmp(dev->name, nla_data(devname_attr), IFNAMSIZ)) {
>+			dev_put(dev);
>+			NL_SET_ERR_MSG_ATTR(extack, nest,
>+					    "ifindex and name do not match");
>+			return -ENODEV;
>+		}
>+	} else if (devname_attr) {
>+		dev = dev_get_by_name(net, nla_data(devname_attr));
>+		if (!dev) {
>+			NL_SET_ERR_MSG_ATTR(extack, devname_attr,
>+					    "no device matches name");
>+			return -ENODEV;
>+		}
>+	} else if (require_dev) {
>+		NL_SET_ERR_MSG_ATTR(extack, nest,
>+				    "neither ifindex nor name specified");
>+		return -EINVAL;
>+	}
>+
>+	if (dev && !netif_device_present(dev)) {
>+		dev_put(dev);
>+		NL_SET_ERR_MSG(extack, "device not present");
>+		return -ENODEV;
>+	}
>+
>+	req_info->dev = dev;
>+	ethnl_update_u32(&req_info->req_mask, tb[ETHTOOL_A_HEADER_INFOMASK]);
>+	ethnl_update_u32(&req_info->global_flags, tb[ETHTOOL_A_HEADER_GFLAGS]);
>+	ethnl_update_u32(&req_info->req_flags, tb[ETHTOOL_A_HEADER_RFLAGS]);

Just:
	req_info->req_mask = nla_get_u32(tb[ETHTOOL_A_HEADER_INFOMASK];
	...

Not sure what ethnl_update_u32() is good for, but it is not needed here.


>+
>+	return 0;
>+}
>+
>+/**
>+ * ethnl_fill_reply_header() - Put standard header into a reply message
>+ * @skb:      skb with the message
>+ * @dev:      network device to describe in header
>+ * @attrtype: attribute type to use for the nest
>+ *
>+ * Create a nested attribute with attributes describing given network device.
>+ * Clean up on error.

Cleanup is obvious, no need to mention it in API docs.


>+ *
>+ * Return: 0 on success, error value (-EMSGSIZE only) on error
>+ */
>+int ethnl_fill_reply_header(struct sk_buff *skb, struct net_device *dev,
>+			    u16 attrtype)
>+{
>+	struct nlattr *nest;
>+
>+	if (!dev)
>+		return 0;
>+	nest = nla_nest_start(skb, attrtype);
>+	if (!nest)
>+		return -EMSGSIZE;
>+
>+	if (nla_put_u32(skb, ETHTOOL_A_HEADER_DEV_INDEX, (u32)dev->ifindex) ||
>+	    nla_put_string(skb, ETHTOOL_A_HEADER_DEV_NAME, dev->name))
>+		goto nla_put_failure;
>+	/* If more attributes are put into reply header, ethnl_header_size()
>+	 * must be updated to account for them.
>+	 */
>+
>+	nla_nest_end(skb, nest);
>+	return 0;
>+
>+nla_put_failure:
>+	nla_nest_cancel(skb, nest);
>+	return -EMSGSIZE;
>+}
>+
>+/**
>+ * ethnl_reply_init() - Create skb for a reply and fill device identification
>+ * @payload: payload length (without netlink and genetlink header)
>+ * @dev:     device the reply is about (may be null)
>+ * @cmd:     ETHTOOL_MSG_* message type for reply
>+ * @info:    genetlink info of the received packet we respond to
>+ * @ehdrp:   place to store payload pointer returned by genlmsg_new()
>+ *
>+ * Return: pointer to allocated skb on success, NULL on error
>+ */
>+struct sk_buff *ethnl_reply_init(size_t payload, struct net_device *dev, u8 cmd,
>+				 u16 hdr_attrtype, struct genl_info *info,
>+				 void **ehdrp)
>+{
>+	struct sk_buff *skb;
>+
>+	skb = genlmsg_new(payload, GFP_KERNEL);
>+	if (!skb)
>+		goto err;
>+	*ehdrp = genlmsg_put_reply(skb, info, &ethtool_genl_family, 0, cmd);
>+	if (!*ehdrp)
>+		goto err_free;
>+
>+	if (dev) {
>+		int ret;
>+
>+		ret = ethnl_fill_reply_header(skb, dev, hdr_attrtype);
>+		if (ret < 0)
>+			goto err;
>+	}
>+	return skb;
>+
>+err_free:
>+	nlmsg_free(skb);
>+	if (info)
>+		GENL_SET_ERR_MSG(info, "failed to setup reply message");
>+err:

Why also not fillup extack msg here?


>+	return NULL;
>+}
>+
> /* genetlink setup */
> 
> static const struct genl_ops ethtool_genl_ops[] = {
>diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
>index 257ae55ccc82..5510eb7054b3 100644
>--- a/net/ethtool/netlink.h
>+++ b/net/ethtool/netlink.h
>@@ -6,5 +6,150 @@
> #include <linux/ethtool_netlink.h>
> #include <linux/netdevice.h>
> #include <net/genetlink.h>
>+#include <net/sock.h>
>+
>+struct ethnl_req_info;
>+
>+int ethnl_parse_header(struct ethnl_req_info *req_info,
>+		       const struct nlattr *nest, struct net *net,
>+		       struct netlink_ext_ack *extack,
>+		       const struct nla_policy *policy, bool require_dev);
>+int ethnl_fill_reply_header(struct sk_buff *skb, struct net_device *dev,
>+			    u16 attrtype);
>+struct sk_buff *ethnl_reply_init(size_t payload, struct net_device *dev, u8 cmd,
>+				 u16 hdr_attrtype, struct genl_info *info,
>+				 void **ehdrp);
>+
>+static inline int ethnl_str_size(const char *s)

If you really need this helper, put it into netlink code. There's nothing
ethtool-specific about this.


>+{
>+	return nla_total_size(strlen(s) + 1);
>+}
>+
>+/* The ethnl_update_* helpers set value pointed to by @dst to the value of
>+ * netlink attribute @attr (if attr is not null). They return true if *dst
>+ * value was changed, false if not.
>+ */
>+static inline bool ethnl_update_u32(u32 *dst, struct nlattr *attr)

I'm still not sure I'm convinced about these "update helpers" :)


>+{
>+	u32 val;
>+
>+	if (!attr)
>+		return false;
>+	val = nla_get_u32(attr);
>+	if (*dst == val)
>+		return false;
>+
>+	*dst = val;
>+	return true;
>+}
>+
>+static inline bool ethnl_update_u8(u8 *dst, struct nlattr *attr)
>+{
>+	u8 val;
>+
>+	if (!attr)
>+		return false;
>+	val = nla_get_u8(attr);
>+	if (*dst == val)
>+		return false;
>+
>+	*dst = val;
>+	return true;
>+}
>+
>+/* update u32 value used as bool from NLA_U8 attribute */
>+static inline bool ethnl_update_bool32(u32 *dst, struct nlattr *attr)
>+{
>+	u8 val;
>+
>+	if (!attr)
>+		return false;
>+	val = !!nla_get_u8(attr);
>+	if (!!*dst == val)
>+		return false;
>+
>+	*dst = val;
>+	return true;
>+}
>+
>+static inline bool ethnl_update_binary(u8 *dst, unsigned int len,

void *dst


>+				       struct nlattr *attr)
>+{
>+	if (!attr)
>+		return false;
>+	if (nla_len(attr) < len)
>+		len = nla_len(attr);
>+	if (!memcmp(dst, nla_data(attr), len))
>+		return false;
>+
>+	memcpy(dst, nla_data(attr), len);
>+	return true;
>+}
>+
>+static inline bool ethnl_update_bitfield32(u32 *dst, struct nlattr *attr)
>+{
>+	struct nla_bitfield32 change;
>+	u32 newval;
>+
>+	if (!attr)
>+		return false;
>+	change = nla_get_bitfield32(attr);
>+	newval = (*dst & ~change.selector) | (change.value & change.selector);
>+	if (*dst == newval)
>+		return false;
>+
>+	*dst = newval;
>+	return true;
>+}
>+
>+/**
>+ * ethnl_is_privileged() - check if request has sufficient privileges
>+ * @skb: skb with client request
>+ *
>+ * Checks if client request has CAP_NET_ADMIN in its netns. Unlike the flags
>+ * in genl_ops, this allows finer access control, e.g. allowing or denying
>+ * the request based on its contents or witholding only part of the data
>+ * from unprivileged users.
>+ *
>+ * Return: true if request is privileged, false if not
>+ */
>+static inline bool ethnl_is_privileged(struct sk_buff *skb)

I wonder why you need this helper. Genetlink uses
ops->flags & GENL_ADMIN_PERM for this. 


>+{
>+	struct net *net = sock_net(skb->sk);
>+
>+	return netlink_ns_capable(skb, net->user_ns, CAP_NET_ADMIN);
>+}
>+
>+/**
>+ * ethnl_reply_header_size() - total size of reply header
>+ *
>+ * This is an upper estimate so that we do not need to hold RTNL lock longer
>+ * than necessary (to prevent rename between size estimate and composing the

I guess this description is not relevant anymore. I don't see why to
hold rtnl mutex for this function...


>+ * message). Accounts only for device ifindex and name as those are the only
>+ * attributes ethnl_fill_reply_header() puts into the reply header.
>+ */
>+static inline unsigned int ethnl_reply_header_size(void)
>+{
>+	return nla_total_size(nla_total_size(sizeof(u32)) +
>+			      nla_total_size(IFNAMSIZ));
>+}
>+
>+/**
>+ * struct ethnl_req_info - base type of request information for GET requests
>+ * @dev:          network device the request is for (may be null)
>+ * @req_mask:     request mask, bitmap of requested information
>+ * @global_flags: request flags common for all request types
>+ * @req_flags:    request flags specific for each request type
>+ * @privileged:   privileged request (CAP_NET_ADMIN in netns)
>+ *
>+ * This is a common base, additional members may follow after this structure.
>+ */
>+struct ethnl_req_info {
>+	struct net_device		*dev;
>+	u32				req_mask;
>+	u32				global_flags;
>+	u32				req_flags;
>+	bool				privileged;
>+};
> 
> #endif /* _NET_ETHTOOL_NETLINK_H */
>-- 
>2.22.0
>

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