[PATCH] nullb: Prevent use of legacy request queue mode

[Damien Le Moal]

When null_blk queue mode is specified together with modprobe/insmod, a
check to prevent setting the nullb device queue mode to 1 (NULL_Q_RQ) is
done. However, the same check is not performed when setting up a nullb
device through configfs, resulting in a oops (NULL pointer dereference
for the device request queue).

Fix this problem by checking for an invalid queue mode value in
null_validate_conf(), propagating -EINVAL to null_add_dev() if the queue
mode is NULL_Q_RQ. While at it, also fix the propagation to user space
of null_add_dev() return value when a nullb device is created through
configfs power attribute.

Fixes: 49f6613632f9 ("nullb: remove leftover legacy request code")
Cc: sta...@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lem...@wdc.com>
---
 drivers/block/null_blk_main.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
index 62c9654b9ce8..5570d0da59b4 100644
--- a/drivers/block/null_blk_main.c
+++ b/drivers/block/null_blk_main.c
@@ -318,9 +318,10 @@ static ssize_t nullb_device_power_store(struct config_item 
*item,
        if (!dev->power && newp) {
                if (test_and_set_bit(NULLB_DEV_FL_UP, &dev->flags))
                        return count;
-               if (null_add_dev(dev)) {
+               ret = null_add_dev(dev);
+               if (ret) {
                        clear_bit(NULLB_DEV_FL_UP, &dev->flags);
-                       return -ENOMEM;
+                       return ret;
                }
 
                set_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags);
@@ -1561,8 +1562,13 @@ static int null_init_tag_set(struct nullb *nullb, struct 
blk_mq_tag_set *set)
        return blk_mq_alloc_tag_set(set);
 }
 
-static void null_validate_conf(struct nullb_device *dev)
+static int null_validate_conf(struct nullb_device *dev)
 {
+       if (dev->queue_mode == NULL_Q_RQ) {
+               pr_err("null_blk: legacy IO path no longer available\n");
+               return -EINVAL;
+       }
+
        dev->blocksize = round_down(dev->blocksize, 512);
        dev->blocksize = clamp_t(unsigned int, dev->blocksize, 512, 4096);
 
@@ -1588,6 +1594,8 @@ static void null_validate_conf(struct nullb_device *dev)
        /* can not stop a queue */
        if (dev->queue_mode == NULL_Q_BIO)
                dev->mbps = 0;
+
+       return 0;
 }
 
 #ifdef CONFIG_BLK_DEV_NULL_BLK_FAULT_INJECTION
@@ -1620,7 +1628,9 @@ static int null_add_dev(struct nullb_device *dev)
        struct nullb *nullb;
        int rv;
 
-       null_validate_conf(dev);
+       rv = null_validate_conf(dev);
+       if (rv)
+               goto out;
 
        nullb = kzalloc_node(sizeof(*nullb), GFP_KERNEL, dev->home_node);
        if (!nullb) {
@@ -1648,8 +1658,10 @@ static int null_add_dev(struct nullb_device *dev)
                if (rv)
                        goto out_cleanup_queues;
 
-               if (!null_setup_fault())
+               if (!null_setup_fault()) {
+                       rv = -EINVAL;
                        goto out_cleanup_queues;
+               }
 
                nullb->tag_set->timeout = 5 * HZ;
                nullb->q = blk_mq_init_queue(nullb->tag_set);
-- 
2.20.1