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SubjectRe: [PATCH-next] scsi: fix use-after-free problem in scsi_remove_target
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On 2/12/23 19:43, Zhong Jinghua wrote:
> T0 T1
> sdev_store_delete
> scsi_remove_device
> device_remove_file
> __scsi_remove_device
> __iscsi_unbind_session
> scsi_remove_target
> spin_lock_irqsave
> list_for_each_entry
> scsi_target_reap // starget->reaf 1 -> 0

What is "reaf"? Did you perhaps want to write "reap_ref"?

> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index e7893835b99a..0ad357ff4c59 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -1561,7 +1561,17 @@ void scsi_remove_target(struct device *dev)
> starget->state == STARGET_CREATED_REMOVE)
> continue;
> if (starget->dev.parent == dev || &starget->dev == dev) {
> - kref_get(&starget->reap_ref);
> +
> + /*
> + * If starget->reap_ref is reduced to 0, it means
> + * that other processes are releasing it and
> + * there is no need to delete it again
> + */
> + if (!kref_get_unless_zero(&starget->reap_ref)) {
> + spin_unlock_irqrestore(shost->host_lock, flags);
> + goto restart;
> + }
> +
> if (starget->state == STARGET_CREATED)
> starget->state = STARGET_CREATED_REMOVE;
> else

The above comment should be made more clear, e.g. as follows: "If the
reference count is already zero, skip this target. Calling
kref_get_unless_zero() if the reference count is zero is safe because
scsi_target_destroy() will wait until the host lock has been released
before freeing starget."

Otherwise this patch looks fine to me.

Thanks,

Bart.

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