Yikes, sorry this languished so long, comments below:
On Mon, Jun 15, 2020 at 12:48 AM Richard Palethorpe
<rpalethorpe(a)suse.com> wrote:
It is possible to cause a division error and use-after-free by querying the
nmem device before the driver data is fully initialised in nvdimm_probe. E.g
by doing
(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
On 5.7-rc3 this causes:
[ 12.711578] divide error: 0000 [#1] SMP KASAN PTI
[ 12.714857] RIP: 0010:nd_label_nfree+0x134/0x1a0 [libnvdimm]
[..]
[ 12.725308] CR2: 00007fd16f1ec000 CR3: 0000000064322006 CR4:
0000000000160ef0
[ 12.726268] Call Trace:
[ 12.726633] available_slots_show+0x4e/0x120 [libnvdimm]
[ 12.727380] dev_attr_show+0x42/0x80
[ 12.727891] ? memset+0x20/0x40
[ 12.728341] sysfs_kf_seq_show+0x218/0x410
[ 12.728923] seq_read+0x389/0xe10
[ 12.729415] vfs_read+0x101/0x2d0
[ 12.729891] ksys_read+0xf9/0x1d0
[ 12.730361] ? kernel_write+0x120/0x120
[ 12.730915] do_syscall_64+0x95/0x4a0
[ 12.731435] entry_SYSCALL_64_after_hwframe+0x49/0xb3
[..]
Fixes: 4d88a97aa9e8 ("libnvdimm, nvdimm: dimm driver and base
libnvdimm device-driver infrastructure")
Cc: Dan Williams <dan.j.williams(a)intel.com>
Cc: Vishal Verma <vishal.l.verma(a)intel.com>
Cc: Dave Jiang <dave.jiang(a)intel.com>
Cc: Ira Weiny <ira.weiny(a)intel.com>
Cc: linux-nvdimm(a)lists.01.org
Cc: linux-kernel(a)vger.kernel.org
Cc: Coly Li <colyli(a)suse.com>
Signed-off-by: Richard Palethorpe <rpalethorpe(a)suse.com>
---
V2:
+ Reviewed by Coly and removed unecessary lock
drivers/nvdimm/dimm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/nvdimm/dimm.c b/drivers/nvdimm/dimm.c
index 7d4ddc4d9322..3d3988e1d9a0 100644
--- a/drivers/nvdimm/dimm.c
+++ b/drivers/nvdimm/dimm.c
@@ -43,7 +43,6 @@ static int nvdimm_probe(struct device *dev)
if (!ndd)
return -ENOMEM;
- dev_set_drvdata(dev, ndd);
ndd->dpa.name = dev_name(dev);
ndd->ns_current = -1;
ndd->ns_next = -1;
@@ -106,6 +105,8 @@ static int nvdimm_probe(struct device *dev)
if (rc)
goto err;
+ dev_set_drvdata(dev, ndd);
+
I see why this works, but I think the bug is in
available_slots_show(). It is a bug for a sysfs attribute to reference
driver-data without synchronizing against bind. So it should be
possible for probe set that pointer whenever it wants. In other words
this fix (forgive the whitespace damage from pasting).
diff --git a/drivers/nvdimm/dimm_devs.c b/drivers/nvdimm/dimm_devs.c
index b59032e0859b..e68b17bc7aab 100644
--- a/drivers/nvdimm/dimm_devs.c
+++ b/drivers/nvdimm/dimm_devs.c
@@ -335,10 +335,8 @@ 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);
ssize_t rc;
u32 nfree;
@@ -356,6 +354,18 @@ 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,