diff --git a/drivers/infiniband/sw/siw/siw_qp_rx.c b/drivers/infiniband/sw/siw/siw_qp_rx.c
index e8a88b378d51..34d03584160c 100644
--- a/drivers/infiniband/sw/siw/siw_qp_rx.c
+++ b/drivers/infiniband/sw/siw/siw_qp_rx.c
@@ -1081,6 +1081,21 @@ static int siw_get_hdr(struct siw_rx_stream *srx)
 			return -EAGAIN;
 	}
 
+	/*
+	 * Peer-controlled mpa_len must not underflow srx->fpdu_part_rem
+	 * in siw_tcp_rx_data(); a negative value flows as a signed copy
+	 * length into siw_check_mem() and skb_copy_bits().
+	 */
+	if (unlikely(be16_to_cpu(c_hdr->mpa_len) + MPA_HDR_SIZE <
+		     iwarp_pktinfo[opcode].hdr_len)) {
+		pr_warn_ratelimited("siw: short mpa_len %u for opcode %u (hdr_len %u)\n",
+				    be16_to_cpu(c_hdr->mpa_len), opcode,
+				    iwarp_pktinfo[opcode].hdr_len);
+		siw_init_terminate(rx_qp(srx), TERM_ERROR_LAYER_LLP,
+				   LLP_ETYPE_MPA, LLP_ECODE_FPDU_START, 0);
+		return -EINVAL;
+	}
+
 	/*
 	 * DDP/RDMAP header receive completed. Check if the current
 	 * DDP segment starts a new RDMAP message or continues a previously