This is a note to let you know that I've just added the patch titled libnvdimm/dimm: Avoid race between probe and available_slots_show() to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: libnvdimm-dimm-avoid-race-between-probe-and-available_slots_show.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Mon Mar 1 01:45:34 PM CET 2021 From: Dan Williams <dan.j.williams@xxxxxxxxx> Date: Mon, 1 Feb 2021 16:20:40 -0800 Subject: libnvdimm/dimm: Avoid race between probe and available_slots_show() From: Dan Williams <dan.j.williams@xxxxxxxxx> commit 7018c897c2f243d4b5f1b94bc6b4831a7eab80fb upstream 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@xxxxxxxxxxxxxxx> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx> Cc: Dave Jiang <dave.jiang@xxxxxxxxx> Cc: Ira Weiny <ira.weiny@xxxxxxxxx> Cc: Coly Li <colyli@xxxxxxxx> Reported-by: Richard Palethorpe <rpalethorpe@xxxxxxxx> Acked-by: Richard Palethorpe <rpalethorpe@xxxxxxxx> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> [sudip: use device_lock()] Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/nvdimm/dimm_devs.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) --- a/drivers/nvdimm/dimm_devs.c +++ b/drivers/nvdimm/dimm_devs.c @@ -359,16 +359,16 @@ static ssize_t state_show(struct device } 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) { @@ -380,6 +380,18 @@ static ssize_t available_slots_show(stru nvdimm_bus_unlock(dev); return rc; } + +static ssize_t available_slots_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + ssize_t rc; + + device_lock(dev); + rc = __available_slots_show(dev_get_drvdata(dev), buf); + device_unlock(dev); + + return rc; +} static DEVICE_ATTR_RO(available_slots); static struct attribute *nvdimm_attributes[] = { Patches currently in stable-queue which might be from dan.j.williams@xxxxxxxxx are queue-4.19/libnvdimm-dimm-avoid-race-between-probe-and-available_slots_show.patch