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Drivers: hv: utils: fix crash when device is removed from host side 

The crash is observed when a service is being disabled host side while
userspace daemon is connected to the device:

[   90.244859] general protection fault: 0000 [#1] SMP
...
[   90.800082] Call Trace:
[   90.800082]  [<ffffffff81187008>] __fput+0xc8/0x1f0
[   90.800082]  [<ffffffff8118716e>] ____fput+0xe/0x10
...
[   90.800082]  [<ffffffff81015278>] do_signal+0x28/0x580
[   90.800082]  [<ffffffff81086656>] ? finish_task_switch+0xa6/0x180
[   90.800082]  [<ffffffff81443ebf>] ? __schedule+0x28f/0x870
[   90.800082]  [<ffffffffa01ebbaa>] ? hvt_op_read+0x12a/0x140 [hv_utils]
...

The problem is that hvutil_transport_destroy() which does misc_deregister()
freeing the appropriate device is reachable by two paths: module unload
and from util_remove(). While module unload path is protected by .owner in
struct file_operations util_remove() path is not. Freeing the device while
someone holds an open fd for it is a show stopper.

In general, it is not possible to revoke an fd from all users so the only
way to solve the issue is to defer freeing the hvutil_transport structure.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Vitaly Kuznetsov 2015-12-14 19:01:56 -08:00 committed by Greg Kroah-Hartman
parent a15025660d
commit 9420098adc
1 changed files with 23 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
drivers/hv/hv_utils_transport.c
View File

@ -155,13 +155,22 @@ static int hvt_op_open(struct inode *inode, struct file *file)
return ret;
}
static void hvt_transport_free(struct hvutil_transport *hvt)
{
misc_deregister(&hvt->mdev);
kfree(hvt->outmsg);
kfree(hvt);
}
static int hvt_op_release(struct inode *inode, struct file *file)
{
struct hvutil_transport *hvt;
int mode_old;
hvt = container_of(file->f_op, struct hvutil_transport, fops);
mutex_lock(&hvt->lock);
mode_old = hvt->mode;
if (hvt->mode != HVUTIL_TRANSPORT_DESTROY)
hvt->mode = HVUTIL_TRANSPORT_INIT;
/*
@ -171,6 +180,9 @@ static int hvt_op_release(struct inode *inode, struct file *file)
hvt_reset(hvt);
mutex_unlock(&hvt->lock);
if (mode_old == HVUTIL_TRANSPORT_DESTROY)
hvt_transport_free(hvt);
return 0;
}
@ -304,17 +316,25 @@ err_free_hvt:
void hvutil_transport_destroy(struct hvutil_transport *hvt)
{
int mode_old;
mutex_lock(&hvt->lock);
mode_old = hvt->mode;
hvt->mode = HVUTIL_TRANSPORT_DESTROY;
wake_up_interruptible(&hvt->outmsg_q);
mutex_unlock(&hvt->lock);
/*
* In case we were in 'chardev' mode we still have an open fd so we
* have to defer freeing the device. Netlink interface can be freed
* now.
*/
spin_lock(&hvt_list_lock);
list_del(&hvt->list);
spin_unlock(&hvt_list_lock);
if (hvt->cn_id.idx > 0 && hvt->cn_id.val > 0)
cn_del_callback(&hvt->cn_id);
misc_deregister(&hvt->mdev);
kfree(hvt->outmsg);
kfree(hvt);
if (mode_old != HVUTIL_TRANSPORT_CHARDEV)
hvt_transport_free(hvt);
}