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 (c_hdr->mpa_len, 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 siw_get_hdr() based on iwarp_pktinfo[opcode]

.hdr_len, but never compares mpa_len against that header length.

siw_tcp_rx_data() then derives

srx->fpdu_part_rem = be16_to_cpu(mpa_len) - fpdu_part_rcvd

+ MPA_HDR_SIZE;

where fpdu_part_rcvd equals iwarp_pktinfo[opcode].hdr_len at this

point. For a tagged WRITE (hdr_len 16, MPA_HDR_SIZE 2) the smallest

on-wire mpa_len of 0 yields fpdu_part_rem = -14, and any mpa_len below

hdr_len - MPA_HDR_SIZE underflows to a negative int.

The signed value then flows into siw_proc_write()/siw_proc_rresp() as

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

is handed to siw_check_mem() 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 siw_rx_data() -> siw_rx_kva() /

siw_rx_umem() -> skb_copy_bits() as a signed copy length. The header

copy branch in skb_copy_bits() 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 AF_INET socketpair, the malformed FPDU written via

kernel_sendmsg, sk_data_ready firing in softirq, tcp_read_sock

dispatching to siw_tcp_rx_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. iwarp_pktinfo[*].hdr_len - MPA_HDR_SIZE is exactly

the value the siw transmitter uses as the minimum mpa_len for each

opcode (drivers/infiniband/sw/siw/siw_qp.c:33), so this matches the

protocol contract. Out-of-range FPDUs terminate the connection with

TERM_ERROR_LAYER_LLP / LLP_ETYPE_MPA / LLP_ECODE_FPDU_START -- 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.