Subject: Re: [PATCH net-next v12 1/4] net netlink: Add new type NLA_BITFIELD32

From: Jiri Pirko <[email-masked]>
Date: Sun, 30 Jul 2017 20:42:42 +0200

Sun, Jul 30, 2017 at 07:24:49PM CEST, [email-masked] wrote:
>From: Jamal Hadi Salim <[email-masked]>
>
>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 <[email-masked]>
>Signed-off-by: Jamal Hadi Salim <[email-masked]>
>---
> include/net/netlink.h        | 16 ++++++++++++++++
> include/uapi/linux/netlink.h | 17 +++++++++++++++++
> lib/nlattr.c                 | 30 ++++++++++++++++++++++++++++++
> 3 files changed, 63 insertions(+)
>
>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 },

Checkpatch warns you about the line to long, please wrap it.

Btw, I did not see you reached a consensus with DavidA regarding this.
Did I miss it?

>  * };
>  */
> 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 @@
> 	[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;

I pointed this out already. This weird.
You do *u32 = *u32, just with different name. Just use valid_flags_allowed
directly.

>+
>+	if (!valid_flags_allowed)
>+		return -EINVAL;
>+
>+	/*disallow invalid bit selector */

Fix all the comments in this function. Should be
	/* something */
with spaces in front and at the end.

>+	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);
>-- 
>1.9.1
>