net netlink: Add new type NLA_BITFIELD32

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

The value is a bitmap that defines the bit values being set
The selector is a bitmask that defines which value bit is to be
considered.

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_BITFIELD32, .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:
value = 0x0, and selector = 0x1
implies we are selecting bit 1 and we want to set its value to 0.

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

Suggested-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 63 insertions, 0 deletions

diff --git a/include/net/netlink.h b/include/net/netlink.h
index ef8e6c3..82dd298 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -178,6 +178,7 @@ enum {
 	NLA_S16,
 	NLA_S32,
 	NLA_S64,
+	NLA_BITFIELD32,
 	__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_BITFIELD32      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_BITFIELD32, .validation_data = &myvalidflags },
  * };
  */
 struct nla_policy {
 	u16		type;
 	u16		len;
+	void            *validation_data;
 };
 
 /**
@@ -1203,6 +1207,18 @@ static inline struct in6_addr nla_get_in6_addr(const struct nlattr *nla)
 }
 
 /**
+ * nla_get_bitfield32 - return payload of 32 bitfield attribute
+ * @nla: nla_bitfield32 attribute
+ */
+static inline struct nla_bitfield32 nla_get_bitfield32(const struct nlattr *nla)
+{
+	struct nla_bitfield32 tmp;
+
+	nla_memcpy(&tmp, nla, sizeof(tmp));
+	return tmp;
+}
+
+/**
  * nla_memdup - duplicate attribute memory (kmemdup)
  * @src: netlink attribute to duplicate from
  * @gfp: GFP mask
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index f86127a..f4fc9c9 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 value is a bitmap that defines the values being set
+ * The selector is a bitmask that defines which value is legit
+ *
+ * Examples:
+ *  value = 0x0, and selector = 0x1
+ *  implies we are selecting bit 1 and we want to set its value to 0.
+ *
+ *  value = 0x2, and selector = 0x2
+ *  implies we are selecting bit 2 and we want to set its value to 1.
+ *
+ */
+struct nla_bitfield32 {
+	__u32 value;
+	__u32 selector;
+};
 
 #endif /* _UAPI__LINUX_NETLINK_H */
diff --git a/lib/nlattr.c b/lib/nlattr.c
index fb52435..ee79b7a 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -27,6 +27,30 @@ static const u8 nla_attr_minlen[NLA_TYPE_MAX+1] = {
 	[NLA_S64]	= sizeof(s64),
 };
 
+static int validate_nla_bitfield32(const struct nlattr *nla,
+				   u32 *valid_flags_allowed)
+{
+	const struct nla_bitfield32 *bf = nla_data(nla);
+	u32 *valid_flags_mask = valid_flags_allowed;
+
+	if (!valid_flags_allowed)
+		return -EINVAL;
+
+	/*disallow invalid bit selector */
+	if (bf->selector & ~*valid_flags_mask)
+		return -EINVAL;
+
+	/*disallow invalid bit values */
+	if (bf->value & ~*valid_flags_mask)
+		return -EINVAL;
+
+	/*disallow valid bit values that are not selected*/
+	if (bf->value & ~bf->selector)
+		return -EINVAL;
+
+	return 0;
+}
+
 static int validate_nla(const struct nlattr *nla, int maxtype,
 			const struct nla_policy *policy)
 {
@@ -46,6 +70,12 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 			return -ERANGE;
 		break;
 
+	case NLA_BITFIELD32:
+		if (attrlen != sizeof(struct nla_bitfield32))
+			return -ERANGE;
+
+		return validate_nla_bitfield32(nla, pt->validation_data);
+
 	case NLA_NUL_STRING:
 		if (pt->len)
 			minlen = min_t(int, attrlen, pt->len + 1);