RDMA/rxe: Fix ref count error in check_rkey()

BugLink: https://bugs.launchpad.net/bugs/2033931
[ Upstream commit b00683422fd79dd07c9b75efdce1660e5e19150e ]

There is a reference count error in error path code and a potential race
in check_rkey() in rxe_resp.c. When looking up the rkey for a memory
window the reference to the mw from rxe_lookup_mw() is dropped before a
reference is taken on the mr referenced by the mw. If the mr is destroyed
immediately after the call to rxe_put(mw) the mr pointer is unprotected
and may end up pointing at freed memory. The rxe_get(mr) call should take
place before the rxe_put(mw) call.

All errors in check_rkey() call rxe_put(mw) if mw is not NULL but it was
already called after the above. The mw pointer should be set to NULL after
the rxe_put(mw) call to prevent this from happening.

Fixes: cdd0b85675ae ("RDMA/rxe: Implement memory access through MWs")
Link: https://lore.kernel.org/r/20230517211509.1819998-1-rpearsonhpe@gmail.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
index 8c68340502769746b854549e76371574c56e9f4e..4e8d8bec0010be558c79652fb5c4865c5c801fdf 100644 (file)
--- a/drivers/infiniband/sw/rxe/rxe_resp.c
+++ b/drivers/infiniband/sw/rxe/rxe_resp.c
@@ -519,8 +519,9 @@ static enum resp_states check_rkey(struct rxe_qp *qp,
                if (mw->access & IB_ZERO_BASED)
                        qp->resp.offset = mw->addr;
 
-               rxe_put(mw);
                rxe_get(mr);
+               rxe_put(mw);
+               mw = NULL;
        } else {
                mr = lookup_mr(qp->pd, access, rkey, RXE_LOOKUP_REMOTE);
                if (!mr) {