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Subject[PATCH] block: fix bsg_unregister and bsg_open race
The existing implementation allows races between bsg_unregister and
bsg_open paths. bsg_ungegister and request_queue cleanup and
deletion may start and complete right after bsg_get_device (in bsg_open path)
retrieves bsg_class_device and releases the mutex. Then bsg_open path
touches freed memory of bsg_class_device and request_queue.

One possible fix is to hold the mutex all the way through bsg_get_device
instead of releasing it after bsg_class_device retrieval.

From a8647f9cfb3b2b69dcac493554cb6ea2f9b4c2dd Mon Sep 17 00:00:00 2001
From: Anatoliy Glagolev <glagolig@gmail.com>
Date: Wed, 13 Jun 2018 15:38:51 -0600
Subject: [PATCH] Fix race of bsg_open and bsg_unregister
Signed-Off-By: Anatoliy Glagolev <glagolig@gmail.com>

---
block/bsg.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/bsg.c b/block/bsg.c
index 132e657..10bc6a4 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -693,6 +693,8 @@ static struct bsg_device *bsg_add_device(struct inode *inode,
struct bsg_device *bd;
unsigned char buf[32];

+ lockdep_assert_held(&bsg_mutex);
+
if (!blk_get_queue(rq))
return ERR_PTR(-ENXIO);

@@ -707,14 +709,12 @@ static struct bsg_device *bsg_add_device(struct inode *inode,
bsg_set_block(bd, file);

atomic_set(&bd->ref_count, 1);
- mutex_lock(&bsg_mutex);
hlist_add_head(&bd->dev_list, bsg_dev_idx_hash(iminor(inode)));

strncpy(bd->name, dev_name(rq->bsg_dev.class_dev), sizeof(bd->name) - 1);
bsg_dbg(bd, "bound to <%s>, max queue %d\n",
format_dev_t(buf, inode->i_rdev), bd->max_queue);

- mutex_unlock(&bsg_mutex);
return bd;
}

@@ -722,7 +722,7 @@ static struct bsg_device *__bsg_get_device(int minor, struct request_queue *q)
{
struct bsg_device *bd;

- mutex_lock(&bsg_mutex);
+ lockdep_assert_held(&bsg_mutex);

hlist_for_each_entry(bd, bsg_dev_idx_hash(minor), dev_list) {
if (bd->queue == q) {
@@ -732,7 +732,6 @@ static struct bsg_device *__bsg_get_device(int minor, struct request_queue *q)
}
bd = NULL;
found:
- mutex_unlock(&bsg_mutex);
return bd;
}

@@ -746,16 +745,18 @@ static struct bsg_device *bsg_get_device(struct inode *inode, struct file *file)
*/
mutex_lock(&bsg_mutex);
bcd = idr_find(&bsg_minor_idr, iminor(inode));
- mutex_unlock(&bsg_mutex);

if (!bcd)
return ERR_PTR(-ENODEV);

bd = __bsg_get_device(iminor(inode), bcd->queue);
- if (bd)
+ if (bd) {
+ mutex_unlock(&bsg_mutex);
return bd;
+ }

bd = bsg_add_device(inode, bcd->queue, file);
+ mutex_unlock(&bsg_mutex);

return bd;
}
--
1.9.1
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