CVE-2026-74582packet: use consistent hard_header_len in non-ring send paths

Official description

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 packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/bcd4df60ac9481b1ceffdfe5ec38fe51dcaae812
• https://git.kernel.org/stable/c/78a47127e33c340bc6d38dcc4552a094b4f5cc77
• https://git.kernel.org/stable/c/142e287b3a25cfe909215177c23243e7fc5ae2b1
• https://git.kernel.org/stable/c/91f041451f967cd87ed722a8f43c0b767a64f1a0
• https://git.kernel.org/stable/c/9052756290962ffb9a661bcf319e92dedaaedfed
• https://git.kernel.org/stable/c/5bb10753d428aadfc356a2bfe9acea09c82a62ec
• https://git.kernel.org/stable/c/b06b6fce6d7deaf7238e09b48ce3b1125ff41acd
• https://git.kernel.org/stable/c/03390aa32e669cc4ecd7d34108e2e1afc13d689d