CVE-2026-98482nfc: llcp: drop truncated I/RR/RNR PDUs in nfc_llcp_recv_hdlc()

Official description

In the Linux kernel, the following vulnerability has been resolved: nfc: llcp: drop truncated I/RR/RNR PDUs in nfc_llcp_recv_hdlc() nfc_llcp_recv_hdlc() reads the sequence byte skb->data[2], via nfc_llcp_ns()/nfc_llcp_nr(), before any length check. The receive path only guarantees the two-byte LLCP header -- __nfc_llcp_recv() checks it with pskb_may_pull() and nfc_llcp_recv_agf() admits two-byte inner PDUs -- so a two-byte I, RR or RNR PDU reads one byte of uninitialised skb tailroom. The byte becomes N(R)/N(S); a peer can already set those with a well-formed PDU, so this is acting on uninitialised memory, not new peer control. Guard the read with pskb_may_pull(), as commit 95674f506c63 ("nfc: llcp: reject PDUs shorter than the LLCP header") did for the two-byte header, so the sequence byte is present and linear before it is read. RR and RNR PDUs are LLCP_HEADER_SIZE + LLCP_SEQUENCE_SIZE bytes and an I PDU is longer, so no valid frame is rejected; a truncated PDU is malformed, so return without a DM reply.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/3afdbebfee2ef7e9510880868cfb482cbffe6836
• https://git.kernel.org/stable/c/9b4086eb67a9a3b1ce69fef1b6793827363703ce
• https://git.kernel.org/stable/c/51b6d73373589abb9de4d84767b0db1bc8d395d9
• https://git.kernel.org/stable/c/066205553a0106565bcede934f5721c25ebd6e4e
• https://git.kernel.org/stable/c/18f60ee882403d5b48097f5f6ae45f794e4cc643
• https://git.kernel.org/stable/c/810f204ef8f61f0c930cf6b3280050b3ee6a8ae7
• https://git.kernel.org/stable/c/744e61bd06188d8bb068c26a461c252f242b05c9
• https://git.kernel.org/stable/c/273f9d667cde649f8de9d72b1303cc2f4b658c50