[PATCH] RDMA/rxe: bound the ODP page index against the umem in rxe_check_pagefault()

[Youngsung Ahn <ays511.kr@gmail.com>]

An ODP MR's page array map.pfn_list[] is sized from the umem's
start, but rxe_check_pagefault() indexes it with an iova taken
relative to that start, while the access was range-checked against
the MR's iova (ibmr.iova). reg_mr only requires start and hca_va to
share a page offset, so a user can register with hca_va =
start + N*PAGE, and the index skew (hca_va - start) >> PAGE_SHIFT
then lands out of bounds of pfn_list[], which is read with no bound
check. An unprivileged local user reaches this with a single RDMA
operation on a self-connected rxe QP: observed as a KASAN
slab-out-of-bounds read and, when the out-of-bounds qword looks like
a writable HMM pfn, a write into an attacker-influenced page.

Reject an index that leaves the umem and force the fault path, which
fails the out-of-range access via the umem range check in
ib_umem_odp_map_dma_and_lock(). The downstream pfn_list[] users
(__rxe_odp_mr_copy() and the atomic helpers) run only after a
successful map, so this check protects them as well.

Fixes: 2fae67ab63db ("RDMA/rxe: Add support for Send/Recv/Write/Read with ODP")
Signed-off-by: Youngsung Ahn <ays511.kr@gmail.com>
---
Notes (not part of the commit):
Reproduced on a KASAN x86-64 build of 7.3-rc4 as uid 1000; the data-only write
primitive was used to reach uid 0 on a fully hardened build.
drivers/infiniband/sw/rxe/ is unchanged between 7.3-rc4 (93f51579e7df) and
mainline 551c722f4080 (2026-09-29) and rdma for-next, so both are affected.
Compile-tested (KASAN+RDMA_RXE), not runtime-tested. Found through AI-assisted
review; per Documentation/process/security-bugs.rst this is public and a
reproducer can be shared on request. A maintainer may prefer to also index
relative to ibmr.iova (as the non-ODP rxe_mr_iova_to_index() does) so
legitimately skewed MRs keep working; this patch takes the minimal, safe route.

 drivers/infiniband/sw/rxe/rxe_odp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
index ab21b620e94c..07a30c60fc62 100644
--- a/drivers/infiniband/sw/rxe/rxe_odp.c
+++ b/drivers/infiniband/sw/rxe/rxe_odp.c
@@ -136,6 +136,11 @@ static inline bool rxe_check_pagefault(struct ib_umem_odp *umem_odp, u64 iova,
 	while (addr < iova + length) {
 		idx = (addr - ib_umem_start(umem_odp)) >> umem_odp->page_shift;

+		if (idx >= ib_umem_odp_num_pages(umem_odp)) {
+			need_fault = true;
+			break;
+		}
+
 		if ((umem_odp->map.pfn_list[idx] & access) != access) {
 			need_fault = true;
 			break;
--
2.43.0