[PATCH 5.10.y 4/4] RDMA/rxe: Fix TOCTOU heap overflow in get_srq_wqe

[Bjoern Doebel <doebel@amazon.de>]

From: Tristan Madani <tristmd@gmail.com>

[ Upstream commit 22b8fbded65b8c441b634a185f8da67657df6c50 ]

get_srq_wqe() reads wqe->dma.num_sge from the shared receive queue
buffer, which is mapped into userspace. It validates num_sge against
max_sge, but then re-reads the same field to calculate the memcpy
size. A concurrent userspace thread can modify num_sge between
validation and use, causing a heap buffer overflow when copying the
WQE into qp->resp.srq_wqe.

Read num_sge into a local variable and use it for both the bounds
check and the size calculation.

Fixes: 8700e3e7c485 ("Soft RoCE driver")
Link: https://patch.msgid.link/r/20260518215040.1598586-2-tristan@talencesecurity.com
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[doebel: cherry-picked from v6.1.178 (3cfa2a3adc51), accomodate for context changes]
Signed-off-by: Bjoern Doebel <doebel@amazon.de>
---
 drivers/infiniband/sw/rxe/rxe_resp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
index 55b5146424e61..d22d95f5e2e3c 100644
--- a/drivers/infiniband/sw/rxe/rxe_resp.c
+++ b/drivers/infiniband/sw/rxe/rxe_resp.c
@@ -292,6 +292,7 @@ static enum resp_states get_srq_wqe(struct rxe_qp *qp)
 	struct rxe_queue *q = srq->rq.queue;
 	struct rxe_recv_wqe *wqe;
 	struct ib_event ev;
+	unsigned int num_sge;
 	size_t size;
 
 	if (srq->error)
@@ -306,12 +307,13 @@ static enum resp_states get_srq_wqe(struct rxe_qp *qp)
 	}
 
 	/* don't trust user space data */
-	if (unlikely(wqe->dma.num_sge > srq->rq.max_sge)) {
+	num_sge = wqe->dma.num_sge;
+	if (unlikely(num_sge > srq->rq.max_sge)) {
 		spin_unlock_bh(&srq->rq.consumer_lock);
 		pr_warn("%s: invalid num_sge in SRQ entry\n", __func__);
 		return RESPST_ERR_MALFORMED_WQE;
 	}
-	size = sizeof(*wqe) + wqe->dma.num_sge*sizeof(struct rxe_sge);
+	size = sizeof(*wqe) + num_sge * sizeof(struct rxe_sge);
 	memcpy(&qp->resp.srq_wqe, wqe, size);
 
 	qp->resp.wqe = &qp->resp.srq_wqe.wqe;
-- 
2.50.1