CVE-2026-64102

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

RDMA/siw: Reject MPA FPDU length underflow before signed receive math

A malicious connected siw peer can send an iWARP FPDU whose MPA length field (chdr->mpalen, 16 bit big-endian, peer-controlled) is smaller than the fixed DDP/RDMAP header for the announced opcode. Soft-iWARP parses the full header in siwgethdr() based on iwarppktinfo[opcode] .hdrlen, but never compares mpa_len against that header length.

siwtcprx_data() then derives

srx->fpdu_part_rem = be16_to_cpu(mpa_len) - fpdu_part_rcvd
                     + MPA_HDR_SIZE;

where fpdupartrcvd equals iwarppktinfo[opcode].hdrlen at this point. For a tagged WRITE (hdrlen 16, MPAHDRSIZE 2) the smallest on-wire mpalen of 0 yields fpdupartrem = -14, and any mpalen below hdrlen - MPAHDRSIZE underflows to a negative int.

The signed value then flows into siwprocwrite()/siwprocrresp() as

bytes = min(srx->fpdu_part_rem, srx->skb_new);

is handed to siwcheckmem() as an int len (whose interval check addr + len > mem->va + mem->len is satisfied for a valid base when len is negative), and reaches siwrxdata() -> siwrxkva() / siwrxumem() -> skbcopybits() as a signed copy length. The header copy branch in skbcopybits() promotes that to size_t, producing a multi-gigabyte read.

KASAN under a KUnit harness that drives the real kernel TCP receive path -- a loopback AFINET socketpair, the malformed FPDU written via kernelsendmsg, skdataready firing in softirq, tcpreadsock dispatching to siwtcprx_data -- reports:

BUG: KASAN: use-after-free in skb_copy_bits+0x284/0x480
Read of size 4294967295 at addr ffff888...
Call Trace:
 skb_copy_bits
 siw_rx_kva
 siw_rx_data
 siw_check_mem
 siw_proc_write
 siw_tcp_rx_data
 __tcp_read_sock
 siw_qp_llp_data_ready
 tcp_data_ready
 tcp_data_queue

Add the missing invariant at the earliest point where the peer header is fully assembled. iwarppktinfo[*].hdrlen - MPAHDRSIZE is exactly the value the siw transmitter uses as the minimum mpalen for each opcode (drivers/infiniband/sw/siw/siwqp.c:33), so this matches the protocol contract. Out-of-range FPDUs terminate the connection with TERMERRORLAYERLLP / LLPETYPEMPA / LLPECODEFPDUSTART -- which is RFC 5044 Section 8 error code 3 ("Marker and ULPDU Length fields do not agree on the start of an FPDU"), the correct framing-error class for this inconsistency.