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: stable@vger.kernel.org Cc: Vishal Verma vishal.l.verma@intel.com Cc: Dave Jiang dave.jiang@intel.com Cc: Ira Weiny ira.weiny@intel.com Cc: Coly Li colyli@suse.com Reported-by: Richard Palethorpe rpalethorpe@suse.com Signed-off-by: Dan Williams dan.j.williams@intel.com --- drivers/nvdimm/dimm_devs.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/nvdimm/dimm_devs.c b/drivers/nvdimm/dimm_devs.c index b59032e0859b..9d208570d059 100644 --- a/drivers/nvdimm/dimm_devs.c +++ b/drivers/nvdimm/dimm_devs.c @@ -335,16 +335,16 @@ static ssize_t state_show(struct device *dev, struct device_attribute *attr, } static DEVICE_ATTR_RO(state);

-static ssize_t available_slots_show(struct device *dev, - struct device_attribute *attr, char *buf) +static ssize_t __available_slots_show(struct nvdimm_drvdata *ndd, char *buf) { - struct nvdimm_drvdata *ndd = dev_get_drvdata(dev); + struct device *dev; ssize_t rc; u32 nfree;

if (!ndd) return -ENXIO;

+ dev = ndd->dev; nvdimm_bus_lock(dev); nfree = nd_label_nfree(ndd); if (nfree - 1 > nfree) { @@ -356,6 +356,18 @@ static ssize_t available_slots_show(struct device *dev, nvdimm_bus_unlock(dev); return rc; } + +static ssize_t available_slots_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + ssize_t rc; + + nd_device_lock(dev); + rc = __available_slots_show(dev_get_drvdata(dev), buf); + nd_device_unlock(dev); + + return rc; +} static DEVICE_ATTR_RO(available_slots);

__weak ssize_t security_show(struct device *dev,