libnvdimm/dimm: Avoid race between probe and available_slots_show()

Richard reports that the following test:

(while true; do
     cat /sys/bus/nd/devices/nmem*/available_slots 2>&1 > /dev/null
 done) &

while true; do
     for i in $(seq 0 4); do
         echo nmem$i > /sys/bus/nd/drivers/nvdimm/bind
     done
     for i in $(seq 0 4); do
         echo nmem$i > /sys/bus/nd/drivers/nvdimm/unbind
     done
 done

...fails with a crash signature like:

    divide error: 0000 [#1] SMP KASAN PTI
    RIP: 0010:nd_label_nfree+0x134/0x1a0 [libnvdimm]
    [..]
    Call Trace:
     available_slots_show+0x4e/0x120 [libnvdimm]
     dev_attr_show+0x42/0x80
     ? memset+0x20/0x40
     sysfs_kf_seq_show+0x218/0x410

The root cause is that available_slots_show() consults driver-data, but
fails to synchronize against device-unbind setting up a TOCTOU race to
access uninitialized memory.

Validate driver-data under the device-lock.

Fixes: 4d88a97aa9e8 ("libnvdimm, nvdimm: dimm driver and base libnvdimm device-driver infrastructure")
Cc: <[email protected]>
Cc: Vishal Verma <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Coly Li <[email protected]>
Reported-by: Richard Palethorpe <[email protected]>
Acked-by: Richard Palethorpe <[email protected]>
Signed-off-by: Dan Williams <[email protected]>

0 files changed, 0 insertions, 0 deletions