CVE ID :CVE-2024-14040<\/p>\n
Published : July 26, 2026, 7:16 a.m. | 37\u00a0minutes ago<\/p>\n
Description :In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
net: nexthop: Increase weight to u16<\/p>\n
In CLOS networks, as link failures occur at various points in the network,
\nECMP weights of the involved nodes are adjusted to compensate. With high
\nfan-out of the involved nodes, and overall high number of nodes,
\na (non-)ECMP weight ratio that we would like to configure does not fit into
\n8 bits. Instead of, say, 255:254, we might like to configure something like
\n1000:999. For these deployments, the 8-bit weight may not be enough.<\/p>\n
To that end, in this patch increase the next hop weight from u8 to u16.<\/p>\n
Increasing the width of an integral type can be tricky, because while the
\ncode still compiles, the types may not check out anymore, and numerical
\nerrors come up. To prevent this, the conversion was done in two steps.
\nFirst the type was changed from u8 to a single-member structure, which
\ninvalidated all uses of the field. This allowed going through them one by
\none and audit for type correctness. Then the structure was replaced with a
\nvanilla u16 again. This should ensure that no place was missed.<\/p>\n
The UAPI for configuring nexthop group members is that an attribute
\nNHA_GROUP carries an array of struct nexthop_grp entries:<\/p>\n
\tstruct nexthop_grp {
\n\t\t__u32\tid;\t \/* nexthop id – must exist *\/
\n\t\t__u8\tweight; \/* weight of this nexthop *\/
\n\t\t__u8\tresvd1;
\n\t\t__u16\tresvd2;
\n\t};<\/p>\n
The field resvd1 is currently validated and required to be zero. We can
\nlift this requirement and carry high-order bits of the weight in the
\nreserved field:<\/p>\n
\tstruct nexthop_grp {
\n\t\t__u32\tid;\t \/* nexthop id – must exist *\/
\n\t\t__u8\tweight; \/* weight of this nexthop *\/
\n\t\t__u8\tweight_high;
\n\t\t__u16\tresvd2;
\n\t};<\/p>\n
Keeping the fields split this way was chosen in case an existing userspace
\nmakes assumptions about the width of the weight field, and to sidestep any
\nendianness issues.<\/p>\n
The weight field is currently encoded as the weight value minus one,
\nbecause weight of 0 is invalid. This same trick is impossible for the new
\nweight_high field, because zero must mean actual zero. With this in place:<\/p>\n
– Old userspace is guaranteed to carry weight_high of 0, therefore
\n configuring 8-bit weights as appropriate. When dumping nexthops with
\n 16-bit weight, it would only show the lower 8 bits. But configuring such
\n nexthops implies existence of userspace aware of the extension in the
\n first place.<\/p>\n
– New userspace talking to an old kernel will work as long as it only
\n attempts to configure 8-bit weights, where the high-order bits are zero.
\n Old kernel will bounce attempts at configuring >8-bit weights.<\/p>\n
Renaming reserved fields as they are allocated for some purpose is commonly
\ndone in Linux. Whoever touches a reserved field is doing so at their own
\nrisk. nexthop_grp::resvd1 in particular is currently used by at least
\nstrace, however they carry an own copy of UAPI headers, and the conversion
\nshould be trivial. A helper is provided for decoding the weight out of the
\ntwo fields. Forcing a conversion seems preferable to bending backwards and
\nintroducing anonymous unions or whatever.<\/p>\n
Severity: 0.0 | NA<\/p>\n
Visit the link for more details, such as CVSS details, affected products, timeline, and more…\u00a0<\/p>\n","protected":false},"excerpt":{"rendered":"
CVE ID :CVE-2024-14040 Published : July 26, 2026, 7:16 a.m. | 37\u00a0minutes ago Description :In the Linux kernel, the following vulnerability has been resolved: net: nexthop: Increase weight to u16 In CLOS networks, as link failures occur at various points in the network, ECMP weights of the involved nodes are adjusted to compensate. With high …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"class_list":["post-82557","post","type-post","status-publish","format-standard","hentry","category-vulnerability"],"_links":{"self":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/82557","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/comments?post=82557"}],"version-history":[{"count":0,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/82557\/revisions"}],"wp:attachment":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/media?parent=82557"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/categories?post=82557"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/tags?post=82557"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}