ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()

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Summary

CVECVE-2026-31531
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-23 12:17:01 UTC
Updated2026-04-28 17:38:49 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop() When querying a nexthop object via RTM_GETNEXTHOP, the kernel currently allocates a fixed-size skb using NLMSG_GOODSIZE. While sufficient for single nexthops and small Equal-Cost Multi-Path groups, this fixed allocation fails for large nexthop groups like 512 nexthops. This results in the following warning splat: WARNING: net/ipv4/nexthop.c:3395 at rtm_get_nexthop+0x176/0x1c0, CPU#20: rep/4608 [...] RIP: 0010:rtm_get_nexthop (net/ipv4/nexthop.c:3395) [...] Call Trace: <TASK> rtnetlink_rcv_msg (net/core/rtnetlink.c:6989) netlink_rcv_skb (net/netlink/af_netlink.c:2550) netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344) netlink_sendmsg (net/netlink/af_netlink.c:1894) ____sys_sendmsg (net/socket.c:721 net/socket.c:736 net/socket.c:2585) ___sys_sendmsg (net/socket.c:2641) __sys_sendmsg (net/socket.c:2671) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) </TASK> Fix this by allocating the size dynamically using nh_nlmsg_size() and using nlmsg_new(), this is consistent with nexthop_notify() behavior. In addition, adjust nh_nlmsg_size_grp() so it calculates the size needed based on flags passed. While at it, also add the size of NHA_FDB for nexthop group size calculation as it was missing too. This cannot be reproduced via iproute2 as the group size is currently limited and the command fails as follows: addattr_l ERROR: message exceeded bound of 1048

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.000100000 probability, percentile 0.011770000 (date 2026-04-26)

Problem Types: NVD-CWE-noinfo

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 430a049190de3c9e219f43084de9f1122da04570 615517f3f8d53b0cf41507c7599971e17adfdfa5 git Not specified
CNA Linux Linux affected 430a049190de3c9e219f43084de9f1122da04570 40bd39e383a0478fd5c221f393df05fd9d70cfbc git Not specified
CNA Linux Linux affected 430a049190de3c9e219f43084de9f1122da04570 635038fe19db391117e66b46bdc2b6e447ac801d git Not specified
CNA Linux Linux affected 430a049190de3c9e219f43084de9f1122da04570 14cf0cd35361f4e94824bf8a42f72713d7702a73 git Not specified
CNA Linux Linux affected 5.3 Not specified
CNA Linux Linux unaffected 5.3 semver Not specified
CNA Linux Linux unaffected 6.12.83 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.24 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.14 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/615517f3f8d53b0cf41507c7599971e17adfdfa5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/635038fe19db391117e66b46bdc2b6e447ac801d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/40bd39e383a0478fd5c221f393df05fd9d70cfbc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/14cf0cd35361f4e94824bf8a42f72713d7702a73 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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