[PATCH v3] ubi: block: fix null-pointer-dereference in ubiblock_create()

[linan666 at huaweicloud.com]

From: Li Nan <linan122 at huawei.com>

Similar to commit adbf4c4954e3 ("ubi: block: fix memleak in
ubiblock_create()"), 'dev->gd' is not assigned but dereferenced if
blk_mq_alloc_tag_set() fails, and leading to a null-pointer-dereference.
Fix it by using pr_err() and variable 'dev' to print error log.

Additionally, the log in the error handle path of idr_alloc() has
been improved by using pr_err(), too. Before initializing device
name, using dev_err() will print error log with 'null' instead of
the actual device name, like this:
  block (null): ...
        ~~~~~~
It is unclear. Using pr_err() can print more details of the device.
The improved log is:
  ubiblock0_0: ...

Fixes: 77567b25ab9f ("ubi: use blk_mq_alloc_disk and blk_cleanup_disk")
Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
Signed-off-by: Li Nan <linan122 at huawei.com>
---
v3: spliting this patch into two in v2 is not a good idea. This version
is consistent with v1, but only optimizes the commit message.

 drivers/mtd/ubi/block.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
index f82e3423acb9..bf7308e8ec2f 100644
--- a/drivers/mtd/ubi/block.c
+++ b/drivers/mtd/ubi/block.c
@@ -390,7 +390,8 @@ int ubiblock_create(struct ubi_volume_info *vi)
 
 	ret = blk_mq_alloc_tag_set(&dev->tag_set);
 	if (ret) {
-		dev_err(disk_to_dev(dev->gd), "blk_mq_alloc_tag_set failed");
+		pr_err("ubiblock%d_%d: blk_mq_alloc_tag_set failed\n",
+			dev->ubi_num, dev->vol_id);
 		goto out_free_dev;
 	}
 
@@ -407,8 +408,8 @@ int ubiblock_create(struct ubi_volume_info *vi)
 	gd->minors = 1;
 	gd->first_minor = idr_alloc(&ubiblock_minor_idr, dev, 0, 0, GFP_KERNEL);
 	if (gd->first_minor < 0) {
-		dev_err(disk_to_dev(gd),
-			"block: dynamic minor allocation failed");
+		pr_err("ubiblock%d_%d: block: dynamic minor allocation failed\n",
+			dev->ubi_num, dev->vol_id);
 		ret = -ENODEV;
 		goto out_cleanup_disk;
 	}
-- 
2.39.2