CVE-2026-74582

About vulnerability

In the Linux kernel, the following vulnerability has been resolved:

packet: use consistent hard_header_len in non-ring send paths

packet_snd() reads dev->hard_header_len multiple times while allocating and constructing an skb. Device reconfiguration can change this value concurrently, for example through bonding device type changes.

For SOCK_RAW, packet_snd() can save a larger value in reserve and later allocate headroom using a smaller value. Moving skb->data back by reserve then places it before skb->head, and the following copy from userspace can attempt an out-of-bounds write.

packet_sendmsg_spkt() has the same issue because it calculates its reservation and header offset from separate reads before dropping the RCU read lock to allocate the skb.

Add LL_RESERVED_SPACE_EX() for callers that already saved a header length. Read hard_header_len once in packet_snd() and use it for allocation and construction. In packet_sendmsg_spkt(), preserve the allocation-time value through the device lookup retry.

The separate SOCK_DGRAM consistency problem between hard_header_len and header_ops->create is not addressed here.

Affected product:

AlmaLinux 9.2 ESU , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , Debian 10 ELS , Debian 11 ELS , TuxCare 9.6 ESU , Ubuntu 20.04 ELS

Affected packages:

linux @ 5.4.0 (+7 more)

Live-patch status from KernelCare for each operating system.