[PATCH net v2] RDMA/rxe: Fix integer overflow in mr_check_range() leading to OOB access

[Gang Yan <gang.yan@linux.dev>]

From: Gang Yan <yangang@kylinos.cn>

mr_check_range() validates that [iova, iova+length) falls within the
registered MR range using wraparound-prone arithmetic:

    if (iova < mr->ibmr.iova ||
        iova + length > mr->ibmr.iova + mr->ibmr.length)

A remote peer can craft an RDMA-Write/Read RETH so that iova + length
wraps to 0 (e.g. iova=0xfffffffffffffff8, length=8), bypassing the
check. rxe_mr_iova_to_index() then computes a huge index (int idx, only
guarded by WARN_ON) and rxe_mr_copy_xarray() dereferences
mr->page_info[huge], causing an out-of-bounds read/write and a kernel
oops that is triggerable by an unauthenticated remote peer.

Rewrite the check in overflow-safe form; the first two clauses guarantee
that the subsequent subtractions do not underflow:

    if (iova < mr->ibmr.iova ||
        length > mr->ibmr.length ||
        iova - mr->ibmr.iova > mr->ibmr.length - length)

With the fix, mr_check_range() returns -EINVAL for the crafted iova and
the responder reports REMOTE_ACCESS_ERROR instead of triggering the OOB.

Assisted-by: Codex: GLM-5.2
Fixes: 8700e3e7c485 ("Soft RoCE driver")
Signed-off-by: Gang Yan <yangang@kylinos.cn>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
---
Changelog:

v2:
  - Add Yanjun's reviewed-by tag as he suggested.
v1:
  Link: https://lore.kernel.org/all/20260728091128.9116-1-gang.yan@linux.dev/
---
 drivers/infiniband/sw/rxe/rxe_mr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c b/drivers/infiniband/sw/rxe/rxe_mr.c
index 875eceb55fdf..71d9ea477289 100644
--- a/drivers/infiniband/sw/rxe/rxe_mr.c
+++ b/drivers/infiniband/sw/rxe/rxe_mr.c
@@ -33,7 +33,8 @@ int mr_check_range(struct rxe_mr *mr, u64 iova, size_t length)
 	case IB_MR_TYPE_USER:
 	case IB_MR_TYPE_MEM_REG:
 		if (iova < mr->ibmr.iova ||
-		    iova + length > mr->ibmr.iova + mr->ibmr.length) {
+		    length > mr->ibmr.length ||
+		    iova - mr->ibmr.iova > mr->ibmr.length - length) {
 			rxe_dbg_mr(mr, "iova/length out of range\n");
 			return -EINVAL;
 		}
-- 
2.43.0