CVE-2026-80731

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

net: remove CAP_SYS_RAWIO zero-padding in dev_validate_header

dev_validate_header() reads dev->hard_header_len directly when

zero-padding short link layer headers for CAP_SYS_RAWIO holders:

if (capable(CAP_SYS_RAWIO)) {

memset(ll_header + len, 0, dev->hard_header_len - len);

return true;

}

Packet send paths call dev_validate_header() on skbs whose headroom was

allocated from an earlier hard_header_len read. If the device is

reconfigured so that dev->hard_header_len increases before validation,

the memset writes past the reserved buffer, an out-of-bounds write.

This out-of-bounds write is masked in some SOCK_RAW paths today because

the same concurrent increase can first make skb_push() exceed the

reserved headroom and trigger skb_under_panic(). Remove the zero-padding

branch before making those hard_header_len reads consistent, so the

snapshot fixes do not turn a loud panic into a silent overwrite.

This path is only reached for variable length L2 protocols, where

len < hard_header_len but len >= min_header_len. No remaining in-tree

variable length L2 protocol implements header_ops->validate, and the

CAP_SYS_RAWIO bypass that zero-pads and accepts short headers has no

real value beyond allowing testing of intentionally malformed input.

Drop the CAP_SYS_RAWIO branch. The remaining reads of

dev->hard_header_len in dev_validate_header() are comparisons only and

have no memory safety impact.