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

Overview

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.

Affected

• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < 683f7cfbf514193d63c0efa079f3352bde84c2e0
• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < 4a331582011d9e8089af8aa2a61ec6b4443bb245
• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < 33a8b5e971e294ec2a7b74211c545e09efd8e9ac
• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < 14553be882d9ce91749c9d64041de66e34ad8e70
• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < c7c0c0f4379dedec12d24dbb9dded5d2db7fd9f2
• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < 1012896f4225e8f801ff3c1648023845b66dfb11
• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < 775b4dc9618a99a1fa48b57554041a5dc17e1336
• Linux >= 8b6a361b8c482f22ac99c3273285ff16b23fba91 < 0ce1bc9e46ecabe84772bb561e373c0d9876d6f2
• Linux 5.3

Remediation

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