There is currently no way to report via extack in a structured way
that an attribute is missing. This leads to families resorting to
string messages.
Add a pair of attributes - @offset and @type for machine-readable
way of reporting missing attributes. The @offset points to the
nest which should have contained the attribute, @type is the
expected nla_type. The offset will be skipped if the attribute
is missing at the message level rather than inside a nest.
User space should be able to figure out which attribute enum
(AKA attribute space AKA attribute set) the nest pointed to by
@offset is using.
Reviewed-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
--
v2: use missing nest as indication of root attrs (Johannes)
v3: add % before NULL in kdoc
make miss_nest a struct nlattr rather than void
---
CC: corbet@xxxxxxx
CC: jacob.e.keller@xxxxxxxxx
CC: fw@xxxxxxxxx
CC: razor@xxxxxxxxxxxxx
CC: linux-doc@xxxxxxxxxxxxxxx
---
Documentation/userspace-api/netlink/intro.rst | 7 +++++--
include/linux/netlink.h | 13 +++++++++++++
include/uapi/linux/netlink.h | 6 ++++++
net/netlink/af_netlink.c | 12 ++++++++++++
4 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/Documentation/userspace-api/netlink/intro.rst b/Documentation/userspace-api/netlink/intro.rst
index 94337f79e077..8f1220756412 100644
--- a/Documentation/userspace-api/netlink/intro.rst
+++ b/Documentation/userspace-api/netlink/intro.rst
@@ -359,8 +359,8 @@ compatibility this feature has to be explicitly enabled by setting
the ``NETLINK_EXT_ACK`` setsockopt() to ``1``.
Types of extended ack attributes are defined in enum nlmsgerr_attrs.
-The two most commonly used attributes are ``NLMSGERR_ATTR_MSG``
-and ``NLMSGERR_ATTR_OFFS``.
+The most commonly used attributes are ``NLMSGERR_ATTR_MSG``,
+``NLMSGERR_ATTR_OFFS`` and ``NLMSGERR_ATTR_MISS_*``.
``NLMSGERR_ATTR_MSG`` carries a message in English describing
the encountered problem. These messages are far more detailed
@@ -368,6 +368,9 @@ than what can be expressed thru standard UNIX error codes.
``NLMSGERR_ATTR_OFFS`` points to the attribute which caused the problem.
+``NLMSGERR_ATTR_MISS_TYPE`` and ``NLMSGERR_ATTR_MISS_NEST``
+inform about a missing attribute.
+
Extended ACKs can be reported on errors as well as in case of success.
The latter should be treated as a warning.
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index bda1c385cffb..1619221c415c 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -71,6 +71,8 @@ netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg)
* %NL_SET_ERR_MSG
* @bad_attr: attribute with error
* @policy: policy for a bad attribute
+ * @miss_type: attribute type which was missing
+ * @miss_nest: nest missing an attribute (%NULL if missing top level attr)
* @cookie: cookie data to return to userspace (for success)
* @cookie_len: actual cookie data length
*/
@@ -78,6 +80,8 @@ struct netlink_ext_ack {
const char *_msg;
const struct nlattr *bad_attr;
const struct nla_policy *policy;
+ const struct nlattr *miss_nest;
+ u16 miss_type;
u8 cookie[NETLINK_MAX_COOKIE_LEN];
u8 cookie_len;
};
@@ -126,6 +130,15 @@ struct netlink_ext_ack {
#define NL_SET_ERR_MSG_ATTR(extack, attr, msg) \
NL_SET_ERR_MSG_ATTR_POL(extack, attr, NULL, msg)
+#define NL_SET_ERR_ATTR_MISS(extack, nest, type) do { \
+ struct netlink_ext_ack *__extack = (extack); \
+ \
+ if (__extack) { \
+ __extack->miss_nest = (nest); \
+ __extack->miss_type = (type); \
+ } \
+} while (0)
+
static inline void nl_set_extack_cookie_u64(struct netlink_ext_ack *extack,
u64 cookie)
{
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index e0ab261ceca2..e0689dbd2cde 100644
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -140,6 +140,10 @@ struct nlmsgerr {
* be used - in the success case - to identify a created
* object or operation or similar (binary)
* @NLMSGERR_ATTR_POLICY: policy for a rejected attribute
+ * @NLMSGERR_ATTR_MISS_TYPE: type of a missing required attribute,
+ * %NLMSGERR_ATTR_MISS_NEST will not be present if the attribute was
+ * missing at the message level
+ * @NLMSGERR_ATTR_MISS_NEST: offset of the nest where attribute was missing
* @__NLMSGERR_ATTR_MAX: number of attributes
* @NLMSGERR_ATTR_MAX: highest attribute number
*/
@@ -149,6 +153,8 @@ enum nlmsgerr_attrs {
NLMSGERR_ATTR_OFFS,
NLMSGERR_ATTR_COOKIE,
NLMSGERR_ATTR_POLICY,
+ NLMSGERR_ATTR_MISS_TYPE,
+ NLMSGERR_ATTR_MISS_NEST,
__NLMSGERR_ATTR_MAX,
NLMSGERR_ATTR_MAX = __NLMSGERR_ATTR_MAX - 1
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 7eae157c1625..f89ba302ac6e 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2423,6 +2423,10 @@ netlink_ack_tlv_len(struct netlink_sock *nlk, int err,
tlvlen += nla_total_size(sizeof(u32));
if (extack->policy)
tlvlen += netlink_policy_dump_attr_size_estimate(extack->policy);
+ if (extack->miss_type)
+ tlvlen += nla_total_size(sizeof(u32));
+ if (extack->miss_nest)
+ tlvlen += nla_total_size(sizeof(u32));
return tlvlen;
}
@@ -2449,6 +2453,14 @@ netlink_ack_tlv_fill(struct sk_buff *in_skb, struct sk_buff *skb,
if (extack->policy)
netlink_policy_dump_write_attr(skb, extack->policy,
NLMSGERR_ATTR_POLICY);
+ if (extack->miss_type)
+ WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_MISS_TYPE,
+ extack->miss_type));
+ if (extack->miss_nest &&
+ !WARN_ON((u8 *)extack->miss_nest < in_skb->data ||
+ (u8 *)extack->miss_nest > in_skb->data + in_skb->len))
+ WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_MISS_NEST,
+ (u8 *)extack->miss_nest - (u8 *)nlh));
}
void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
--
2.37.2
