Bug 2524436 (CVE-2026-74743)

Summary: CVE-2026-74743 kernel: macvlan: inherit needed_headroom and needed_tailroom from lowerdev
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerability-draftAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's macvlan component. The macvlan component incorrectly initializes network packet buffer (skb) headroom and tailroom values, failing to inherit them from the underlying network device. This can occur when the underlying device requires additional space for headers or trailers, such as with macsec or IPsec. This oversight can lead to memory corruption, specifically KASAN slab-use-after-free crashes, potentially resulting in a denial of service.
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Description OSIDB Bzimport 2026-08-26 14:52:35 UTC 
In the Linux kernel, the following vulnerability has been resolved:

macvlan: inherit needed_headroom and needed_tailroom from lowerdev

macvlan devices inherit hard_header_len from lowerdev during macvlan_init(),
but leave needed_headroom and needed_tailroom set to 0.

When the underlying lowerdev requires extra headroom or tailroom for
headers/trailers (e.g. macsec, ipsec, wireguard, tunnels, or veth with rx
headroom), upper layers calculating packet headroom and tailroom fail to
reserve sufficient space.

This can result in reallocation overhead, skb headroom underflows, or KASAN
slab-use-after-free crashes when dev_hard_header() / macvlan_hard_header()
prepends header data or when lower devices append tailroom.

Fix this by:
1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init().
2. Propagating needed_headroom and needed_tailroom updates to attached macvlans
   in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events.
Comment 1 gkamathe 2026-08-27 07:01:18 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082658-CVE-2026-74743-ba1f@gregkh/T