[PATCH] bcache: fix cached_dev.sb_bio use-after-free and crash

[PATCH] bcache: fix cached_dev.sb_bio use-after-free and crash

[mingzhe.zou]

From: Mingzhe Zou <mingzhe.zou@easystack.cn>

In our production environment, we have received multiple crash reports
regarding libceph, which have caught our attention:

```
[6888366.280350] Call Trace:
[6888366.280452]  blk_update_request+0x14e/0x370
[6888366.280561]  blk_mq_end_request+0x1a/0x130
[6888366.280671]  rbd_img_handle_request+0x1a0/0x1b0 [rbd]
[6888366.280792]  rbd_obj_handle_request+0x32/0x40 [rbd]
[6888366.280903]  __complete_request+0x22/0x70 [libceph]
[6888366.281032]  osd_dispatch+0x15e/0xb40 [libceph]
[6888366.281164]  ? inet_recvmsg+0x5b/0xd0
[6888366.281272]  ? ceph_tcp_recvmsg+0x6f/0xa0 [libceph]
[6888366.281405]  ceph_con_process_message+0x79/0x140 [libceph]
[6888366.281534]  ceph_con_v1_try_read+0x5d7/0xf30 [libceph]
[6888366.281661]  ceph_con_workfn+0x329/0x680 [libceph]
```

After analyzing the coredump file, we found that the address of dc->sb_bio
has been freed. We know that cached_dev is only freed when it is stopped.

Since sb_bio is a part of struct cached_dev, rather than an alloc every time.
If the device is stopped while writing to the superblock, the released address
will be accessed at endio.

This patch hopes to wait for sb_write to complete in cached_dev_free.

It should be noted that we analyzed the cause of the problem, then tell
all details to the QWEN and adopted the modifications it made.

Signed-off-by: Mingzhe Zou <mingzhe.zou@easystack.cn>
---
 drivers/md/bcache/super.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 64bb38c95895..6627a381f65a 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1373,6 +1373,13 @@ static CLOSURE_CALLBACK(cached_dev_free)
 
 	mutex_unlock(&bch_register_lock);
 
+	/*
+	 * Wait for any pending sb_write to complete before free.
+	 * The sb_bio is embedded in struct cached_dev, so we must
+	 * ensure no I/O is in progress.
+	 */
+	closure_sync(&dc->sb_write);
+
 	if (dc->sb_disk)
 		folio_put(virt_to_folio(dc->sb_disk));
 
-- 
2.34.1

Re: [PATCH] bcache: fix cached_dev.sb_bio use-after-free and crash

[Coly Li]

On Wed, Mar 18, 2026 at 08:53:49PM +0800, mingzhe.zou@easystack.cn wrote:
> From: Mingzhe Zou <mingzhe.zou@easystack.cn>
> 
> In our production environment, we have received multiple crash reports
> regarding libceph, which have caught our attention:
> 
> ```
> [6888366.280350] Call Trace:
> [6888366.280452]  blk_update_request+0x14e/0x370
> [6888366.280561]  blk_mq_end_request+0x1a/0x130
> [6888366.280671]  rbd_img_handle_request+0x1a0/0x1b0 [rbd]
> [6888366.280792]  rbd_obj_handle_request+0x32/0x40 [rbd]
> [6888366.280903]  __complete_request+0x22/0x70 [libceph]
> [6888366.281032]  osd_dispatch+0x15e/0xb40 [libceph]
> [6888366.281164]  ? inet_recvmsg+0x5b/0xd0
> [6888366.281272]  ? ceph_tcp_recvmsg+0x6f/0xa0 [libceph]
> [6888366.281405]  ceph_con_process_message+0x79/0x140 [libceph]
> [6888366.281534]  ceph_con_v1_try_read+0x5d7/0xf30 [libceph]
> [6888366.281661]  ceph_con_workfn+0x329/0x680 [libceph]
> ```
> 
> After analyzing the coredump file, we found that the address of dc->sb_bio
> has been freed. We know that cached_dev is only freed when it is stopped.
> 
> Since sb_bio is a part of struct cached_dev, rather than an alloc every time.
> If the device is stopped while writing to the superblock, the released address
> will be accessed at endio.
> 
> This patch hopes to wait for sb_write to complete in cached_dev_free.
> 
> It should be noted that we analyzed the cause of the problem, then tell
> all details to the QWEN and adopted the modifications it made.
> 
> Signed-off-by: Mingzhe Zou <mingzhe.zou@easystack.cn>

Nice catch. I will add a Fixes tag and CC stable.

Thanks.

Coly Li

> ---
>  drivers/md/bcache/super.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 64bb38c95895..6627a381f65a 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1373,6 +1373,13 @@ static CLOSURE_CALLBACK(cached_dev_free)
>  
>  	mutex_unlock(&bch_register_lock);
>  
> +	/*
> +	 * Wait for any pending sb_write to complete before free.
> +	 * The sb_bio is embedded in struct cached_dev, so we must
> +	 * ensure no I/O is in progress.
> +	 */
> +	closure_sync(&dc->sb_write);
> +
>  	if (dc->sb_disk)
>  		folio_put(virt_to_folio(dc->sb_disk));
>  
> -- 
> 2.34.1
> 

[PATCH] bcache: fix cached_dev.sb_bio use-after-free and crash

[colyli]

From: Mingzhe Zou <mingzhe.zou@easystack.cn>

In our production environment, we have received multiple crash reports
regarding libceph, which have caught our attention:

```
[6888366.280350] Call Trace:
[6888366.280452]  blk_update_request+0x14e/0x370
[6888366.280561]  blk_mq_end_request+0x1a/0x130
[6888366.280671]  rbd_img_handle_request+0x1a0/0x1b0 [rbd]
[6888366.280792]  rbd_obj_handle_request+0x32/0x40 [rbd]
[6888366.280903]  __complete_request+0x22/0x70 [libceph]
[6888366.281032]  osd_dispatch+0x15e/0xb40 [libceph]
[6888366.281164]  ? inet_recvmsg+0x5b/0xd0
[6888366.281272]  ? ceph_tcp_recvmsg+0x6f/0xa0 [libceph]
[6888366.281405]  ceph_con_process_message+0x79/0x140 [libceph]
[6888366.281534]  ceph_con_v1_try_read+0x5d7/0xf30 [libceph]
[6888366.281661]  ceph_con_workfn+0x329/0x680 [libceph]
```

After analyzing the coredump file, we found that the address of
dc->sb_bio has been freed. We know that cached_dev is only freed when it
is stopped.

Since sb_bio is a part of struct cached_dev, rather than an alloc every
time.  If the device is stopped while writing to the superblock, the
released address will be accessed at endio.

This patch hopes to wait for sb_write to complete in cached_dev_free.

It should be noted that we analyzed the cause of the problem, then tell
all details to the QWEN and adopted the modifications it made.

Signed-off-by: Mingzhe Zou <mingzhe.zou@easystack.cn>
Fixes: cafe563591446 ("bcache: A block layer cache")
Cc: stable@vger.linux.org # 3.10+
Signed-off-by: Coly Li <colyli@fnnas.com>
---
 drivers/md/bcache/super.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 64bb38c95895..6627a381f65a 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1373,6 +1373,13 @@ static CLOSURE_CALLBACK(cached_dev_free)
 
 	mutex_unlock(&bch_register_lock);
 
+	/*
+	 * Wait for any pending sb_write to complete before free.
+	 * The sb_bio is embedded in struct cached_dev, so we must
+	 * ensure no I/O is in progress.
+	 */
+	closure_sync(&dc->sb_write);
+
 	if (dc->sb_disk)
 		folio_put(virt_to_folio(dc->sb_disk));
 
-- 
2.47.3

[PATCH] bcache: fix cached_dev.sb_bio use-after-free and crash

[mingzhe.zou]

From: Mingzhe Zou <mingzhe.zou@easystack.cn>

In our production environment, we have received multiple crash reports
regarding libceph, which have caught our attention:

```
[6888366.280350] Call Trace:
[6888366.280452]  blk_update_request+0x14e/0x370
[6888366.280561]  blk_mq_end_request+0x1a/0x130
[6888366.280671]  rbd_img_handle_request+0x1a0/0x1b0 [rbd]
[6888366.280792]  rbd_obj_handle_request+0x32/0x40 [rbd]
[6888366.280903]  __complete_request+0x22/0x70 [libceph]
[6888366.281032]  osd_dispatch+0x15e/0xb40 [libceph]
[6888366.281164]  ? inet_recvmsg+0x5b/0xd0
[6888366.281272]  ? ceph_tcp_recvmsg+0x6f/0xa0 [libceph]
[6888366.281405]  ceph_con_process_message+0x79/0x140 [libceph]
[6888366.281534]  ceph_con_v1_try_read+0x5d7/0xf30 [libceph]
[6888366.281661]  ceph_con_workfn+0x329/0x680 [libceph]
```

After analyzing the coredump file, we found that the address of dc->sb_bio
has been freed. We know that cached_dev is only freed when it is stopped.

Since sb_bio is a part of struct cached_dev, rather than an alloc every time.
If the device is stopped while writing to the superblock, the released address
will be accessed at endio.

This patch hopes to wait for sb_write to complete in cached_dev_free.

It should be noted that we analyzed the cause of the problem, then tell
all details to the QWEN and adopted the modifications it made.

Signed-off-by: Mingzhe Zou <mingzhe.zou@easystack.cn>
---
 drivers/md/bcache/super.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 64bb38c95895..6627a381f65a 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1373,6 +1373,13 @@ static CLOSURE_CALLBACK(cached_dev_free)
 
 	mutex_unlock(&bch_register_lock);
 
+	/*
+	 * Wait for any pending sb_write to complete before free.
+	 * The sb_bio is embedded in struct cached_dev, so we must
+	 * ensure no I/O is in progress.
+	 */
+	closure_sync(&dc->sb_write);
+
 	if (dc->sb_disk)
 		folio_put(virt_to_folio(dc->sb_disk));
 
-- 
2.34.1