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netlink: export policy in extended ACK

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Add a new attribute NLMSGERR_ATTR_POLICY to the extended ACK
to advertise the policy, e.g. if an attribute was out of range,
you'll know the range that's permissible.

Add new NL_SET_ERR_MSG_ATTR_POL() and NL_SET_ERR_MSG_ATTR_POL()
macros to set this, since realistically it's only useful to do
this when the bad attribute (offset) is also returned.

Use it in lib/nlattr.c which practically does all the policy
validation.

v2:
 - add and use netlink_policy_dump_attr_size_estimate()
v3:
 - remove redundant break
v4:
 - really remove redundant break ... sorry

Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Johannes Berg
2020-10-08 12:45:17 +02:00
committed by Jakub Kicinski
parent d2681e93b0
commit 44f3625bc6
6 changed files with 111 additions and 28 deletions
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61
net/netlink/policy.c
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@@ -196,12 +196,54 @@ bool netlink_policy_dump_loop(struct netlink_policy_dump_state *state)
return !netlink_policy_dump_finished(state);
}
int netlink_policy_dump_attr_size_estimate(const struct nla_policy *pt)
{
/* nested + type */
int common = 2 * nla_attr_size(sizeof(u32));
switch (pt->type) {
case NLA_UNSPEC:
case NLA_REJECT:
/* these actually don't need any space */
return 0;
case NLA_NESTED:
case NLA_NESTED_ARRAY:
/* common, policy idx, policy maxattr */
return common + 2 * nla_attr_size(sizeof(u32));
case NLA_U8:
case NLA_U16:
case NLA_U32:
case NLA_U64:
case NLA_MSECS:
case NLA_S8:
case NLA_S16:
case NLA_S32:
case NLA_S64:
/* maximum is common, u64 min/max with padding */
return common +
2 * (nla_attr_size(0) + nla_attr_size(sizeof(u64)));
case NLA_BITFIELD32:
return common + nla_attr_size(sizeof(u32));
case NLA_STRING:
case NLA_NUL_STRING:
case NLA_BINARY:
/* maximum is common, u32 min-length/max-length */
return common + 2 * nla_attr_size(sizeof(u32));
case NLA_FLAG:
return common;
}
/* this should then cause a warning later */
return 0;
}
static int
__netlink_policy_dump_write_attr(struct netlink_policy_dump_state *state,
struct sk_buff *skb,
const struct nla_policy *pt,
int nestattr)
{
int estimate = netlink_policy_dump_attr_size_estimate(pt);
enum netlink_attribute_type type;
struct nlattr *attr;
@@ -334,12 +376,31 @@ __netlink_policy_dump_write_attr(struct netlink_policy_dump_state *state,
goto nla_put_failure;
nla_nest_end(skb, attr);
WARN_ON(attr->nla_len > estimate);
return 0;
nla_put_failure:
nla_nest_cancel(skb, attr);
return -ENOBUFS;
}
/**
* netlink_policy_dump_write_attr - write a given attribute policy
* @skb: the message skb to write to
* @pt: the attribute's policy
* @nestattr: the nested attribute ID to use
*
* Returns: 0 on success, an error code otherwise; -%ENODATA is
* special, indicating that there's no policy data and
* the attribute is generally rejected.
*/
int netlink_policy_dump_write_attr(struct sk_buff *skb,
const struct nla_policy *pt,
int nestattr)
{
return __netlink_policy_dump_write_attr(NULL, skb, pt, nestattr);
}
/**
* netlink_policy_dump_write - write current policy dump attributes
* @skb: the message skb to write to