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Subject[PATCH 4.5 135/238] bcache: cleaned up error handling around register_cache()
Date
4.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Wheeler <git@linux.ewheeler.net>

commit 9b299728ed777428b3908ac72ace5f8f84b97789 upstream.

Fix null pointer dereference by changing register_cache() to return an int
instead of being void. This allows it to return -ENOMEM or -ENODEV and
enables upper layers to handle the OOM case without NULL pointer issues.

See this thread:
http://thread.gmane.org/gmane.linux.kernel.bcache.devel/3521

Fixes this error:
gargamel:/sys/block/md5/bcache# echo /dev/sdh2 > /sys/fs/bcache/register

bcache: register_cache() error opening sdh2: cannot allocate memory
BUG: unable to handle kernel NULL pointer dereference at 00000000000009b8
IP: [<ffffffffc05a7e8d>] cache_set_flush+0x102/0x15c [bcache]
PGD 120dff067 PUD 1119a3067 PMD 0
Oops: 0000 [#1] SMP
Modules linked in: veth ip6table_filter ip6_tables
(...)
CPU: 4 PID: 3371 Comm: kworker/4:3 Not tainted 4.4.2-amd64-i915-volpreempt-20160213bc1 #3
Hardware name: System manufacturer System Product Name/P8H67-M PRO, BIOS 3904 04/27/2013
Workqueue: events cache_set_flush [bcache]
task: ffff88020d5dc280 ti: ffff88020b6f8000 task.ti: ffff88020b6f8000
RIP: 0010:[<ffffffffc05a7e8d>] [<ffffffffc05a7e8d>] cache_set_flush+0x102/0x15c [bcache]

Signed-off-by: Eric Wheeler <bcache@linux.ewheeler.net>
Tested-by: Marc MERLIN <marc@merlins.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/bcache/super.c | 34 ++++++++++++++++++++++------------
1 file changed, 22 insertions(+), 12 deletions(-)

--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1828,11 +1828,12 @@ static int cache_alloc(struct cache_sb *
return 0;
}

-static void register_cache(struct cache_sb *sb, struct page *sb_page,
+static int register_cache(struct cache_sb *sb, struct page *sb_page,
struct block_device *bdev, struct cache *ca)
{
char name[BDEVNAME_SIZE];
- const char *err = "cannot allocate memory";
+ const char *err = NULL;
+ int ret = 0;

memcpy(&ca->sb, sb, sizeof(struct cache_sb));
ca->bdev = bdev;
@@ -1847,27 +1848,35 @@ static void register_cache(struct cache_
if (blk_queue_discard(bdev_get_queue(ca->bdev)))
ca->discard = CACHE_DISCARD(&ca->sb);

- if (cache_alloc(sb, ca) != 0)
+ ret = cache_alloc(sb, ca);
+ if (ret != 0)
goto err;

- err = "error creating kobject";
- if (kobject_add(&ca->kobj, &part_to_dev(bdev->bd_part)->kobj, "bcache"))
- goto err;
+ if (kobject_add(&ca->kobj, &part_to_dev(bdev->bd_part)->kobj, "bcache")) {
+ err = "error calling kobject_add";
+ ret = -ENOMEM;
+ goto out;
+ }

mutex_lock(&bch_register_lock);
err = register_cache_set(ca);
mutex_unlock(&bch_register_lock);

- if (err)
- goto err;
+ if (err) {
+ ret = -ENODEV;
+ goto out;
+ }

pr_info("registered cache device %s", bdevname(bdev, name));
+
out:
kobject_put(&ca->kobj);
- return;
+
err:
- pr_notice("error opening %s: %s", bdevname(bdev, name), err);
- goto out;
+ if (err)
+ pr_notice("error opening %s: %s", bdevname(bdev, name), err);
+
+ return ret;
}

/* Global interfaces/init */
@@ -1965,7 +1974,8 @@ static ssize_t register_bcache(struct ko
if (!ca)
goto err_close;

- register_cache(sb, sb_page, bdev, ca);
+ if (register_cache(sb, sb_page, bdev, ca) != 0)
+ goto err_close;
}
out:
if (sb_page)

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