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Wed, 30 Sep 2026 11:21:41 -0700 (PDT) Received: from localhost.localdomain ([112.171.72.75]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-88818fe3eedsm36659b3a.32.2026.09.30.11.21.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Sep 2026 11:21:40 -0700 (PDT) From: Youngsung Ahn To: zyjzyj2000@gmail.com Cc: linux-rdma@vger.kernel.org, security@kernel.org Subject: [PATCH] RDMA/rxe: reject IB_WR_REG_MR from user QPs in rxe_reg_fast_mr() Date: Thu, 1 Oct 2026 03:21:26 +0900 Message-ID: <20260930182126.2510559-1-ays511.kr@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit IB_WR_REG_MR is documented as kernel-only ("can not be issued by userspace"), but nothing enforces it. rxe_wr_opcode_info[IB_WR_REG_MR] sets WR_LOCAL_OP_MASK for IB_QPT_RC, a QP type userspace can create, so a user QP that writes opcode = IB_WR_REG_MR into its mmap'd SQ ring reaches rxe_do_local_ops() -> rxe_reg_fast_mr(). That function then trusts the ring-supplied fields: struct rxe_mr *mr = to_rmr(wqe->wr.wr.reg.mr); ... if (unlikely(mr->state != RXE_MR_STATE_FREE)) /* deref */ ... mr->access = access; /* write */ For a user QP wqe->wr.wr.reg.mr is a fully attacker-chosen pointer, so this is an arbitrary-kernel-address dereference (arbitrary read confirmed, oops). No existing check distinguishes a user QP on this path. Reject IB_WR_REG_MR for user QPs before dereferencing the supplied pointer. Fixes: 8700e3e7c485 ("Soft RoCE driver") Signed-off-by: Youngsung Ahn --- Notes (not part of the commit): Reproduced on 7.3-rc4 as uid 1000 (arbitrary-address read dereference / oops). Present unchanged in mainline 551c722f4080 (2026-09-29) and rdma for-next; note that commit 2dac7006b9fb ("RDMA/rxe: Reject IB_ACCESS_ON_DEMAND changes after MR creation") recently touched this function for the ACCESS_ON_DEMAND flag but left the pointer dereference in place. Compile-tested (KASAN+RDMA_RXE), not runtime-tested. Found through manual review; per security-bugs.rst this is public and a reproducer can be shared on request. The Fixes: tag should be refined to the commit that added rxe_reg_fast_mr() when preparing for merge. drivers/infiniband/sw/rxe/rxe_mr.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c b/drivers/infiniband/sw/rxe/rxe_mr.c index 71d9ea477289..3a914c243829 100644 --- a/drivers/infiniband/sw/rxe/rxe_mr.c +++ b/drivers/infiniband/sw/rxe/rxe_mr.c @@ -777,6 +777,10 @@ int rxe_reg_fast_mr(struct rxe_qp *qp, struct rxe_send_wqe *wqe) u32 key = wqe->wr.wr.reg.key; u32 access = wqe->wr.wr.reg.access; + /* IB_WR_REG_MR is a kernel-only op; a user QP must not reach here. */ + if (qp->is_user) + return -EOPNOTSUPP; + /* user can only register MR in free state */ if (unlikely(mr->state != RXE_MR_STATE_FREE)) { rxe_dbg_mr(mr, "mr->lkey = 0x%x not free\n", mr->lkey); -- 2.43.0