IB/uverbs: Fix NULL pointer dereference during device removal
As part of ib_uverbs_remove_one which might be triggered upon
reset flow, we trigger IB_EVENT_DEVICE_FATAL event to userspace
application.
If device was removed after uverbs fd was opened but before
ib_uverbs_get_context was called, the event file will be accessed
before it was allocated, result in NULL pointer dereference:
Fix it by checking that user context was allocated before
trigger the event.
Fixes: 0714e11068da ('IB/uverbs: Enable device removal when there are active user space applications') Signed-off-by: Maor Gottlieb <maorg@mellanox.com> Reviewed-by: Matan Barak <matanb@mellanox.com> Signed-off-by: Leon Romanovsky <leon@kernel.org> Signed-off-by: Doug Ledford <dledford@redhat.com>