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net netlink: Add new type NLA_BITFIELD32

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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 protected]>
Signed-off-by: Jamal Hadi Salim <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Jamal Hadi Salim 2017-07-30 13:24:49 -04:00 • committed by David S. Miller
commit 64c83d8373
3 changed files with 63 additions and 0 deletions
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30
lib/nlattr.c
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@ -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);