net/tls: Consume empty data records in tls_sw_read_sock()

Overview

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

net/tls: Consume empty data records in tls_sw_read_sock()

A peer may send a zero-length TLS application_data record; TLS 1.3 explicitly permits these as a traffic-analysis countermeasure (RFC 8446, Section 5.1). After decryption such a record has full_len == 0. tls_sw_read_sock() hands it to the read_actor, which has no payload to consume and returns zero. The loop treats a zero return as backpressure (used <= 0), requeues the skb at the head of rx_list, and stops. rx_list is serviced head-first on the next call, so the empty record is dequeued, fails the same way, and is requeued again; every later record on the connection is blocked behind it.

tls_sw_recvmsg() does not stall on this: a zero-length data record copies nothing and falls through to consume_skb(). Mirror that in the read_sock() path by recognizing an empty data record before the actor runs, consuming it, and continuing.

Affected

• Linux >= 662fbcec32f4af6bdcf5b4006b792ebe9543d945 < 0867b0f2513ebc1c475af9898c97f4772a68d964
• Linux >= 662fbcec32f4af6bdcf5b4006b792ebe9543d945 < c6b440cf766a557b08d25f1b571b3d57d039686e
• Linux >= 662fbcec32f4af6bdcf5b4006b792ebe9543d945 < e8a4c9fc437b16aef38f86ce3275677e36924259
• Linux >= 662fbcec32f4af6bdcf5b4006b792ebe9543d945 < ebc295ce343600c2d60c1e1e0c5d192080217457
• Linux >= 662fbcec32f4af6bdcf5b4006b792ebe9543d945 < 3be28e2c9cd0230cb51fd4967df095273afd3848
• Linux 6.6

Remediation

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