Re: [PATCH v2] RDMA/rxe: validate inline sge_offset in finish_packet() before indexing inline_data[]

[Leon Romanovsky <leon@kernel.org>]

On Fri, Oct 02, 2026 at 12:24:33AM +0900, Youngsung Ahn wrote:
> For a user QP, rxe_post_send() takes the qp->is_user branch and
> never runs init_send_wqe(), so
> dma.length/resid/num_sge/cur_sge/sge_offset all come straight from
> the mmap'd SQ ring. In the inline send path finish_packet() uses
> sge_offset directly as an index:
> 
> 	u8 *tmp = &wqe->dma.inline_data[wqe->dma.sge_offset];
> 	memcpy(payload_addr(pkt), tmp, payload);
> 
> inline_data is a flex array whose capacity is qp->sq.max_inline, but
> sge_offset is a u32 from user space, so the source pointer is
> displaced arbitrarily past the WQE and the memcpy reads out of
> bounds.
> commit 126c757e4cd4 ("RDMA/rxe: Validate num_sge/cur_sge before indexing wqe->dma.sge[]")
> added num_sge/cur_sge checks on the send path but not sge_offset, the
> third attacker-controlled index in the same struct.
> 
> Read sge_offset once with READ_ONCE() and bound it (and the payload
> that follows it) by qp->sq.max_inline before indexing, so the value
> that is validated is the value that is used.
> 
> Fixes: 8700e3e7c485 ("Soft RoCE driver")
> Cc: stable@vger.kernel.org
> Signed-off-by: Youngsung Ahn <ays511.kr@gmail.com>
> Assisted-by: LLM
> ---
> Notes (not part of the commit):
> Reproduced on 7.3-rc4 as uid 1000: "BUG: unable to handle page fault ...
> memcpy+0xc/0x30" from rxe_requester, 4/4. Present unchanged in mainline
> 551c722f4080 (2026-09-29) and rdma for-next. 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.
> 
> v2: the WQE lives in the mmap'd ring, so read dma.sge_offset once with
> READ_ONCE() into a local and validate/index that local, closing the TOCTOU
> noted in automated review (v1 re-read the field after the bounds check).
> Dropped security@kernel.org Cc.
> 
>  drivers/infiniband/sw/rxe/rxe_req.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)

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