From 690252f19f0e486abb8590b3a7a03d4e065d93d4 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Thu, 25 Aug 2022 20:09:31 -0700 Subject: [PATCH] netlink: add support for ext_ack missing attributes 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 Signed-off-by: Jakub Kicinski Signed-off-by: Paolo Abeni --- 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 94337f7..8f12207 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 bda1c38..1619221 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 e0ab261..e0689db 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 7eae157..f89ba30 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, -- 2.7.4