vlan: ensure sufficient headroom in vlan_dev_hard_header()

Overview

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

vlan: ensure sufficient headroom in vlan_dev_hard_header()

Callers that only reserve ETH_HLEN or less (such as llc_alloc_frame()), or skbs allocated before dynamic device/headroom changes (e.g. toggling VLAN_FLAG_REORDER_HDR or bonding/team switching slaves), can reach vlan_dev_hard_header() with insufficient headroom and trigger skb_under_panic().

Use skb_cow_head() in vlan_dev_hard_header() when VLAN_FLAG_REORDER_HDR is not set to ensure sufficient headroom for the VLAN header(s) and the underlying device hard header.

Use READ_ONCE() to read dev->hard_header_len and dev->needed_headroom as they can be updated concurrently under RTNL (e.g. in vlan_transfer_features()) while vlan_dev_hard_header() runs locklessly on the transmit path. Also avoid LL_RESERVED_SPACE(dev) here so that the extra HH_DATA_MOD alignment padding does not trigger unnecessary pskb_expand_head() reallocations on inner stacked VLAN devices after the outer VLAN header has been pushed.

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 55e007fc3b4d76fa4d6b4660f6904fe6ab045a1b
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 5aca8e6a8ff6aeae358c1d9b65447aac416ace95
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 4ba1f57313f36a3ce6f77d593548f0c511f34aa1
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ca797491f0ae4bfde9039f79f6f1ed7781c9110f
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < cfba0f45553de2b803059e3d539a1e418df24da8
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c7ee4bea64f559ea8e03260014775b64c720cb5b
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 90d51095371d96747f45bbd8504edf6513e039ef
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < cd5dd68267c4238795fadaf02b3575ca3f8a6500
• Linux 2.6.12

Remediation

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