nfc: llcp: reject PDUs shorter than the LLCP header

Overview

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

nfc: llcp: reject PDUs shorter than the LLCP header

Every LLCP PDU begins with a two-byte header (DSAP/SSAP + PTYPE), but the receive path never checked that a frame is at least LLCP_HEADER_SIZE bytes before parsing it.

nfc_llcp_rx_skb() reads the header via nfc_llcp_ptype()/nfc_llcp_dsap()/ nfc_llcp_ssap(), which dereference pdu->data[0] and pdu->data[1], and a CONNECT or CC PDU then computes

tlv_array_len = skb->len - LLCP_HEADER_SIZE;

as a size_t and hands it to the TLV walk. When the frame is shorter than the header the subtraction wraps to a huge value and the walk runs far past the buffer, an out-of-bounds read.

A nearby NFC device can reach this without authentication; LLCP link activation happens automatically after NFC-DEP.

Guard the common receive choke point __nfc_llcp_recv(), shared by both the target (nfc_llcp_data_received()) and initiator (nfc_llcp_recv()) paths, so a short skb is dropped before the rx_work worker parses it. Use pskb_may_pull() rather than a skb->len test so the two header bytes are guaranteed to sit in the skb linear area even for a non-linear skb, matching how the sibling NCI and HCI receive paths validate their headers.

Reproduced with a KFENCE out-of-bounds read via /dev/virtual_nci on linux-next.

Found by 0sec automated security-research tooling (https://0sec.ai).

Affected

• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < e6ec76a68dce04884dfeccfe5a5f0e9f67c0ec82
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < f36cffea24bf3e2cc29a00d4b51dbcadc087d810
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < a7b9b449f5a5132221fff6adc11a9431ab8cd914
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 3793d768b40f38bb97265dd5b9a8b8655c4e1b1d
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < eab47618e282602197db287ecbd1b09d356a2515
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < e969e98410051b1ef8cc318bfe0c7e3f24ec766d
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < ae5f20f5842f440b72d030e3a34fe182dd8eae42
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < d3d90243393c48146911c67fd3792b549d21d9e6
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 95674f506c6376d6722a23144c9acd26609771ed
• Linux 3.3

Remediation

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