netdev - [PATCH net-next v11 1/4] net netlink: Add new type NLA_BITFIELD

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Date:   Sun, 23 Jul 2017 21:35:43 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, xiyou.wangcong@...il.com,
        dsahern@...il.com, eric.dumazet@...il.com, mrv@...atatu.com,
        simon.horman@...ronome.com, alex.aring@...il.com,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: [PATCH net-next v11 1/4] net netlink: Add new type NLA_BITFIELD_32

From: Jamal Hadi Salim <jhs@...atatu.com>

Generic bitflags attribute content sent to the kernel by user.
With this type the user can either set or unset a flag in the
kernel.

The nla_value is a bitmap that defines the values being set
The nla_selector is a bitmask that defines which value is legit.

A check is made to ensure the rules that a kernel subsystem always
conforms to bitflags the kernel already knows about. i.e
if the user tries to set a bit flag that is not understood then
the _it will be rejected_.

In the most basic form, the user specifies the attribute policy as:
[ATTR_GOO] = { .type = NLA_BITFIELD_32, .validation_data = &myvalidflags },

where myvalidflags is the bit mask of the flags the kernel understands.

If the user _does not_ provide myvalidflags then the attribute will
also be rejected.

Examples:
nla_value = 0x0, and nla_selector = 0x1
implies we are selecting bit 1 and we want to set its value to 0.

nla_value = 0x2, and nla_selector = 0x2
implies we are selecting bit 2 and we want to set its value to 1.

Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
---
 include/net/netlink.h        |  4 ++++
 include/uapi/linux/netlink.h | 17 +++++++++++++++++
 lib/nlattr.c                 | 21 +++++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/include/net/netlink.h b/include/net/netlink.h
index ef8e6c3..e33d1fb 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -178,6 +178,7 @@ enum {
 	NLA_S16,
 	NLA_S32,
 	NLA_S64,
+	NLA_BITFIELD_32,
 	__NLA_TYPE_MAX,
 };
 
@@ -206,6 +207,7 @@ enum {
  *    NLA_MSECS            Leaving the length field zero will verify the
  *                         given type fits, using it verifies minimum length
  *                         just like "All other"
+ *    NLA_BITFIELD_32      A 32-bit bitmap/bitselector attribute
  *    All other            Minimum length of attribute payload
  *
  * Example:
@@ -213,11 +215,13 @@ enum {
  * 	[ATTR_FOO] = { .type = NLA_U16 },
  *	[ATTR_BAR] = { .type = NLA_STRING, .len = BARSIZ },
  *	[ATTR_BAZ] = { .len = sizeof(struct mystruct) },
+ *	[ATTR_GOO] = { .type = NLA_BITFIELD_32, .validation_data = &myvalidflags },
  * };
  */
 struct nla_policy {
 	u16		type;
 	u16		len;
+	void            *validation_data;
 };
 
 /**
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index f86127a..0ac05a6 100644
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -226,5 +226,22 @@ struct nlattr {
 #define NLA_ALIGN(len)		(((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1))
 #define NLA_HDRLEN		((int) NLA_ALIGN(sizeof(struct nlattr)))
 
+/* Generic 32 bitflags attribute content sent to the kernel.
+ *
+ * The nla_value is a bitmap that defines the values being set
+ * The nla_selector is a bitmask that defines which value is legit
+ *
+ * Examples:
+ *  nla_value = 0x0, and nla_selector = 0x1
+ *  implies we are selecting bit 1 and we want to set its value to 0.
+ *
+ *  nla_value = 0x2, and nla_selector = 0x2
+ *  implies we are selecting bit 2 and we want to set its value to 1.
+ *
+ */
+struct nla_bitfield_32 {
+	__u32 nla_value;
+	__u32 nla_selector;
+};
 
 #endif /* _UAPI__LINUX_NETLINK_H */
diff --git a/lib/nlattr.c b/lib/nlattr.c
index fb52435..c8aad7e 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -27,6 +27,20 @@
 	[NLA_S64]	= sizeof(s64),
 };
 
+static int validate_nla_bitfield_32(const struct nlattr *nla, void *valid_data)
+{
+	const struct nla_bitfield_32 *nbf = nla_data(nla);
+	u32 *valid_flags_mask = valid_data;
+
+	if (!valid_data)
+		return -EINVAL;
+
+	if (nbf->nla_value & ~*valid_flags_mask)
+		return -EINVAL;
+
+	return 0;
+}
+
 static int validate_nla(const struct nlattr *nla, int maxtype,
 			const struct nla_policy *policy)
 {
@@ -46,6 +60,13 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 			return -ERANGE;
 		break;
 
+	case NLA_BITFIELD_32:
+		if (attrlen != sizeof(struct nla_bitfield_32))
+			return -ERANGE;
+
+		return validate_nla_bitfield_32(nla, pt->validation_data);
+		break;
+
 	case NLA_NUL_STRING:
 		if (pt->len)
 			minlen = min_t(int, attrlen, pt->len + 1);
-- 
1.9.1