Re: [PATCH v2] RDMA/rxe: bound the ODP page index against the umem in rxe_check_pagefault()

[sashiko-bot@kernel.org]

> 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")
> Cc: stable@vger.kernel.org
> Signed-off-by: Youngsung Ahn <ays511.kr@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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