net: remove CAP_SYS_RAWIO zero-padding in dev_validate_header

Overview

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.

Affected

• Linux >= b5518429e70cd783b8ca52335456172c1a0589f6 < 53fd7f912c0877647d6a1e1877f5ea8535ee0b4a
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < fa6d98dd925e72fc028b26a0cbbff9d2f0601ff6
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < 8fc9816404166a90ed8d544dc52482fafffb6d9f
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < b0f92a5731dc82556a9ae005cc35f71ab136307b
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < 99df6b7a713f96eda206680d100b76e15f9d9b69
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < 74e035f07f53feca09e2352e77fccb09cad5e208
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < dbb30dc943a93e083f1e531bfdc6779e57de40d0
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < fc902f52a02298c7432b2334c0c82a2885a1a8b6
• Linux >= 2793a23aacbd754dbbb5cb75093deb7e4103bace < 3b9a324e646d3657a8d9806dfbfe4f3e4066e882
• Linux f58a6c08ebdfa978178bbca78c2ba744a2665912
• Linux 1df16498dfd0d5a129bdf2982d9a08df73e8923d
• Linux 8b8d278aa4de9335682bbd4a3bb619af015c859e
• Linux 6804052fa9d86e9a512c88b24a5debbfc1a490fc
• Linux >= 3.2.80 < 3.2.81
• Linux >= 3.16.36 < 3.17
• Linux >= 4.1.28 < 4.2
• Linux >= 4.4.8 < 4.5
• Linux >= 4.5.2 < 4.6
• Linux 4.6

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.