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CVE-2021-47391
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MITRE ATT&CK
Collection
Command and Control
Credential Access
Defense Evasion
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Execution
Exfiltration
Impact
Initial Access
Lateral Movement
Persistence
Privilege Escalation
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Description
In the Linux kernel, the following vulnerability has been resolved:
RDMA/cma: Ensure rdma_addr_cancel() happens before issuing more requests
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.
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CVE ID
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