[PATCH 5.14 065/172] RDMA/cma: Ensure rdma_addr_cancel() happens before issuing more requests

Greg Kroah-Hartman
2021-10-04T13:35:27Z

From: Jason Gunthorpe <jgg@nvidia.com>

commit 305d568b72f17f674155a2a8275f865f207b3808 upstream.

The FSM can run in a circle allowing rdma_resolve_ip() to be called twice
on the same id_priv. While this cannot happen without going through the
work, it violates the invariant that the same address resolution
background request cannot be active twice.

CPU 1 CPU 2

rdma_resolve_addr():
RDMA_CM_IDLE -> RDMA_CM_ADDR_QUERY
rdma_resolve_ip(addr_handler) #1

process_one_req(): for #1
addr_handler():
RDMA_CM_ADDR_QUERY -> RDMA_CM_ADDR_BOUND
mutex_unlock(&id_priv->handler_mutex);
[.. handler still running ..]

rdma_resolve_addr():
RDMA_CM_ADDR_BOUND -> RDMA_CM_ADDR_QUERY
rdma_resolve_ip(addr_handler)
!! two requests are now on the req_list

rdma_destroy_id():
destroy_id_handler_unlock():
_destroy_id():
cma_cancel_operation():
rdma_addr_cancel()

// process_one_req() self removes it
spin_lock_bh(&lock);
cancel_delayed_work(&req->work);
if (!list_empty(&req->list)) == true

! rdma_addr_cancel() returns after process_on_req #1 is done

kfree(id_priv)

process_one_req(): for #2
addr_handler():
mutex_lock(&id_priv->handler_mutex);
!! Use after free on id_priv

rdma_addr_cancel() expects there to be one req on the list and only
cancels the first one. The self-removal behavior of the work only happens
after the handler has returned. This yields a situations where the
req_list can have two reqs for the same "handle" but rdma_addr_cancel()
only cancels the first one.

The second req remains active beyond rdma_destroy_id() and will
use-after-free id_priv once it inevitably triggers.

Fix this by remembering if the id_priv has called rdma_resolve_ip() and
always cancel before calling it again. This ensures the req_list never
gets more than one item in it and doesn't cost anything in the normal flow
that never uses this strange error path.

Link: https://lore.kernel.org/r/0-v1-3bc675b8006d+22-syz_cancel_uaf_jgg@nvidia.com
Cc: stable@vger.kernel.org
Fixes: e51060f08a61 ("IB: IP address based RDMA connection manager")
Reported-by: syzbot+dc3dfba010d7671e05f5@syzkaller.appspotmail.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/infiniband/core/cma.c | 23 +++++++++++++++++++++++
drivers/infiniband/core/cma_priv.h | 1 +
2 files changed, 24 insertions(+)

--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -1776,6 +1776,14 @@ static void cma_cancel_operation(struct
{
switch (state) {
case RDMA_CM_ADDR_QUERY:
+ /*
+ * We can avoid doing the rdma_addr_cancel() based on state,
+ * only RDMA_CM_ADDR_QUERY has a work that could still execute.
+ * Notice that the addr_handler work could still be exiting
+ * outside this state, however due to the interaction with the
+ * handler_mutex the work is guaranteed not to touch id_priv
+ * during exit.
+ */
rdma_addr_cancel(&id_priv->id.route.addr.dev_addr);
break;
case RDMA_CM_ROUTE_QUERY:
@@ -3410,6 +3418,21 @@ int rdma_resolve_addr(struct rdma_cm_id
if (dst_addr->sa_family == AF_IB) {
ret = cma_resolve_ib_addr(id_priv);
} else {
+ /*
+ * The FSM can return back to RDMA_CM_ADDR_BOUND after
+ * rdma_resolve_ip() is called, eg through the error
+ * path in addr_handler(). If this happens the existing
+ * request must be canceled before issuing a new one.
+ * Since canceling a request is a bit slow and this
+ * oddball path is rare, keep track once a request has
+ * been issued. The track turns out to be a permanent
+ * state since this is the only cancel as it is
+ * immediately before rdma_resolve_ip().
+ */
+ if (id_priv->used_resolve_ip)
+ rdma_addr_cancel(&id->route.addr.dev_addr);
+ else
+ id_priv->used_resolve_ip = 1;
ret = rdma_resolve_ip(cma_src_addr(id_priv), dst_addr,
&id->route.addr.dev_addr,
timeout_ms, addr_handler,
--- a/drivers/infiniband/core/cma_priv.h
+++ b/drivers/infiniband/core/cma_priv.h
@@ -91,6 +91,7 @@ struct rdma_id_private {
u8 afonly;
u8 timeout;
u8 min_rnr_timer;
+ u8 used_resolve_ip;
enum ib_gid_type gid_type;

/*