From: Zqiang <[email protected]>
Fix this by increase object reference count.
BUG: KASAN: use-after-free in __lock_acquire+0x3fd4/0x4180
kernel/locking/lockdep.c:3831
Read of size 8 at addr ffff8880683b0018 by task syz-executor.0/3377
CPU: 1 PID: 3377 Comm: syz-executor.0 Not tainted 5.6.11 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xce/0x128 lib/dump_stack.c:118
print_address_description.constprop.4+0x21/0x3c0 mm/kasan/report.c:374
__kasan_report+0x131/0x1b0 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:641
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
__lock_acquire+0x3fd4/0x4180 kernel/locking/lockdep.c:3831
lock_acquire+0x127/0x350 kernel/locking/lockdep.c:4488
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x35/0x50 kernel/locking/spinlock.c:159
printer_ioctl+0x4a/0x110 drivers/usb/gadget/function/f_printer.c:723
vfs_ioctl fs/ioctl.c:47 [inline]
ksys_ioctl+0xfb/0x130 fs/ioctl.c:763
__do_sys_ioctl fs/ioctl.c:772 [inline]
__se_sys_ioctl fs/ioctl.c:770 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:770
do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4531a9
Code: ed 60 fc ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 0f 83 bb 60 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fd14ad72c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000073bfa8 RCX: 00000000004531a9
RDX: fffffffffffffff9 RSI: 000000000000009e RDI: 0000000000000003
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004bbd61
R13: 00000000004d0a98 R14: 00007fd14ad736d4 R15: 00000000ffffffff
Allocated by task 2393:
save_stack+0x21/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc.constprop.3+0xa7/0xd0 mm/kasan/common.c:515
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
kmem_cache_alloc_trace+0xfa/0x2d0 mm/slub.c:2813
kmalloc include/linux/slab.h:555 [inline]
kzalloc include/linux/slab.h:669 [inline]
gprinter_alloc+0xa1/0x870 drivers/usb/gadget/function/f_printer.c:1416
usb_get_function+0x58/0xc0 drivers/usb/gadget/functions.c:61
config_usb_cfg_link+0x1ed/0x3e0 drivers/usb/gadget/configfs.c:444
configfs_symlink+0x527/0x11d0 fs/configfs/symlink.c:202
vfs_symlink+0x33d/0x5b0 fs/namei.c:4201
do_symlinkat+0x11b/0x1d0 fs/namei.c:4228
__do_sys_symlinkat fs/namei.c:4242 [inline]
__se_sys_symlinkat fs/namei.c:4239 [inline]
__x64_sys_symlinkat+0x73/0xb0 fs/namei.c:4239
do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Freed by task 3368:
save_stack+0x21/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
kasan_set_free_info mm/kasan/common.c:337 [inline]
__kasan_slab_free+0x135/0x190 mm/kasan/common.c:476
kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
slab_free_hook mm/slub.c:1444 [inline]
slab_free_freelist_hook mm/slub.c:1477 [inline]
slab_free mm/slub.c:3034 [inline]
kfree+0xf7/0x410 mm/slub.c:3995
gprinter_free+0x49/0xd0 drivers/usb/gadget/function/f_printer.c:1353
usb_put_function+0x38/0x50 drivers/usb/gadget/functions.c:87
config_usb_cfg_unlink+0x2db/0x3b0 drivers/usb/gadget/configfs.c:485
configfs_unlink+0x3b9/0x7f0 fs/configfs/symlink.c:250
vfs_unlink+0x287/0x570 fs/namei.c:4073
do_unlinkat+0x4f9/0x620 fs/namei.c:4137
__do_sys_unlink fs/namei.c:4184 [inline]
__se_sys_unlink fs/namei.c:4182 [inline]
__x64_sys_unlink+0x42/0x50 fs/namei.c:4182
do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
The buggy address belongs to the object at ffff8880683b0000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 24 bytes inside of
1024-byte region [ffff8880683b0000, ffff8880683b0400)
The buggy address belongs to the page:
page:ffffea0001a0ec00 refcount:1 mapcount:0 mapping:ffff88806c00e300
index:0xffff8880683b1800 compound_mapcount: 0
flags: 0x100000000010200(slab|head)
raw: 0100000000010200 0000000000000000 0000000600000001 ffff88806c00e300
raw: ffff8880683b1800 000000008010000a 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Reported-by: Kyungtae Kim <[email protected]>
Signed-off-by: Zqiang <[email protected]>
---
drivers/usb/gadget/function/f_printer.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index 9c7ed2539ff7..8ed1295d7e35 100644
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -31,6 +31,7 @@
#include <linux/types.h>
#include <linux/ctype.h>
#include <linux/cdev.h>
+#include <linux/kref.h>
#include <asm/byteorder.h>
#include <linux/io.h>
@@ -64,7 +65,7 @@ struct printer_dev {
struct usb_gadget *gadget;
s8 interface;
struct usb_ep *in_ep, *out_ep;
-
+ struct kref kref;
struct list_head rx_reqs; /* List of free RX structs */
struct list_head rx_reqs_active; /* List of Active RX xfers */
struct list_head rx_buffers; /* List of completed xfers */
@@ -218,6 +219,13 @@ static inline struct usb_endpoint_descriptor *ep_desc(struct usb_gadget *gadget,
/*-------------------------------------------------------------------------*/
+static void printer_dev_free(struct kref *kref)
+{
+ struct printer_dev *dev = container_of(kref, struct printer_dev, kref);
+
+ kfree(dev);
+}
+
static struct usb_request *
printer_req_alloc(struct usb_ep *ep, unsigned len, gfp_t gfp_flags)
{
@@ -348,6 +356,7 @@ printer_open(struct inode *inode, struct file *fd)
spin_unlock_irqrestore(&dev->lock, flags);
+ kref_get(&dev->kref);
DBG(dev, "printer_open returned %x\n", ret);
return ret;
}
@@ -365,6 +374,7 @@ printer_close(struct inode *inode, struct file *fd)
dev->printer_status &= ~PRINTER_SELECTED;
spin_unlock_irqrestore(&dev->lock, flags);
+ kref_put(&dev->kref, printer_dev_free);
DBG(dev, "printer_close\n");
return 0;
@@ -1350,7 +1360,8 @@ static void gprinter_free(struct usb_function *f)
struct f_printer_opts *opts;
opts = container_of(f->fi, struct f_printer_opts, func_inst);
- kfree(dev);
+
+ kref_put(&dev->kref, printer_dev_free);
mutex_lock(&opts->lock);
--opts->refcnt;
mutex_unlock(&opts->lock);
@@ -1419,6 +1430,7 @@ static struct usb_function *gprinter_alloc(struct usb_function_instance *fi)
return ERR_PTR(-ENOMEM);
}
+ kref_init(&dev->kref);
++opts->refcnt;
dev->minor = opts->minor;
dev->pnp_string = opts->pnp_string;
--
2.24.1
On Fri, Jun 05, 2020 at 11:56:52AM +0800, [email protected] wrote:
> From: Zqiang <[email protected]>
>
> Fix this by increase object reference count.
>
> BUG: KASAN: use-after-free in __lock_acquire+0x3fd4/0x4180
> kernel/locking/lockdep.c:3831
> Read of size 8 at addr ffff8880683b0018 by task syz-executor.0/3377
>
> CPU: 1 PID: 3377 Comm: syz-executor.0 Not tainted 5.6.11 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0xce/0x128 lib/dump_stack.c:118
> print_address_description.constprop.4+0x21/0x3c0 mm/kasan/report.c:374
> __kasan_report+0x131/0x1b0 mm/kasan/report.c:506
> kasan_report+0x12/0x20 mm/kasan/common.c:641
> __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
> __lock_acquire+0x3fd4/0x4180 kernel/locking/lockdep.c:3831
> lock_acquire+0x127/0x350 kernel/locking/lockdep.c:4488
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x35/0x50 kernel/locking/spinlock.c:159
> printer_ioctl+0x4a/0x110 drivers/usb/gadget/function/f_printer.c:723
> vfs_ioctl fs/ioctl.c:47 [inline]
> ksys_ioctl+0xfb/0x130 fs/ioctl.c:763
> __do_sys_ioctl fs/ioctl.c:772 [inline]
> __se_sys_ioctl fs/ioctl.c:770 [inline]
> __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:770
> do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4531a9
> Code: ed 60 fc ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48
> 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
> 01 f0 ff ff 0f 83 bb 60 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fd14ad72c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 000000000073bfa8 RCX: 00000000004531a9
> RDX: fffffffffffffff9 RSI: 000000000000009e RDI: 0000000000000003
> RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004bbd61
> R13: 00000000004d0a98 R14: 00007fd14ad736d4 R15: 00000000ffffffff
>
> Allocated by task 2393:
> save_stack+0x21/0x90 mm/kasan/common.c:72
> set_track mm/kasan/common.c:80 [inline]
> __kasan_kmalloc.constprop.3+0xa7/0xd0 mm/kasan/common.c:515
> kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
> kmem_cache_alloc_trace+0xfa/0x2d0 mm/slub.c:2813
> kmalloc include/linux/slab.h:555 [inline]
> kzalloc include/linux/slab.h:669 [inline]
> gprinter_alloc+0xa1/0x870 drivers/usb/gadget/function/f_printer.c:1416
> usb_get_function+0x58/0xc0 drivers/usb/gadget/functions.c:61
> config_usb_cfg_link+0x1ed/0x3e0 drivers/usb/gadget/configfs.c:444
> configfs_symlink+0x527/0x11d0 fs/configfs/symlink.c:202
> vfs_symlink+0x33d/0x5b0 fs/namei.c:4201
> do_symlinkat+0x11b/0x1d0 fs/namei.c:4228
> __do_sys_symlinkat fs/namei.c:4242 [inline]
> __se_sys_symlinkat fs/namei.c:4239 [inline]
> __x64_sys_symlinkat+0x73/0xb0 fs/namei.c:4239
> do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 3368:
> save_stack+0x21/0x90 mm/kasan/common.c:72
> set_track mm/kasan/common.c:80 [inline]
> kasan_set_free_info mm/kasan/common.c:337 [inline]
> __kasan_slab_free+0x135/0x190 mm/kasan/common.c:476
> kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
> slab_free_hook mm/slub.c:1444 [inline]
> slab_free_freelist_hook mm/slub.c:1477 [inline]
> slab_free mm/slub.c:3034 [inline]
> kfree+0xf7/0x410 mm/slub.c:3995
> gprinter_free+0x49/0xd0 drivers/usb/gadget/function/f_printer.c:1353
> usb_put_function+0x38/0x50 drivers/usb/gadget/functions.c:87
> config_usb_cfg_unlink+0x2db/0x3b0 drivers/usb/gadget/configfs.c:485
> configfs_unlink+0x3b9/0x7f0 fs/configfs/symlink.c:250
> vfs_unlink+0x287/0x570 fs/namei.c:4073
> do_unlinkat+0x4f9/0x620 fs/namei.c:4137
> __do_sys_unlink fs/namei.c:4184 [inline]
> __se_sys_unlink fs/namei.c:4182 [inline]
> __x64_sys_unlink+0x42/0x50 fs/namei.c:4182
> do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8880683b0000
> which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 24 bytes inside of
> 1024-byte region [ffff8880683b0000, ffff8880683b0400)
> The buggy address belongs to the page:
> page:ffffea0001a0ec00 refcount:1 mapcount:0 mapping:ffff88806c00e300
> index:0xffff8880683b1800 compound_mapcount: 0
> flags: 0x100000000010200(slab|head)
> raw: 0100000000010200 0000000000000000 0000000600000001 ffff88806c00e300
> raw: ffff8880683b1800 000000008010000a 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Reported-by: Kyungtae Kim <[email protected]>
> Signed-off-by: Zqiang <[email protected]>
> ---
> drivers/usb/gadget/function/f_printer.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
> index 9c7ed2539ff7..8ed1295d7e35 100644
> --- a/drivers/usb/gadget/function/f_printer.c
> +++ b/drivers/usb/gadget/function/f_printer.c
> @@ -31,6 +31,7 @@
> #include <linux/types.h>
> #include <linux/ctype.h>
> #include <linux/cdev.h>
> +#include <linux/kref.h>
>
> #include <asm/byteorder.h>
> #include <linux/io.h>
> @@ -64,7 +65,7 @@ struct printer_dev {
> struct usb_gadget *gadget;
> s8 interface;
> struct usb_ep *in_ep, *out_ep;
> -
> + struct kref kref;
> struct list_head rx_reqs; /* List of free RX structs */
> struct list_head rx_reqs_active; /* List of Active RX xfers */
> struct list_head rx_buffers; /* List of completed xfers */
Isn't there already a reference count for this structure? Why not use
that instead?
If not, should this be done to all gadget drivers? What makes this one
unique?
thanks,
greg k-h
I cannot find a reference count for this structure(printer_dev).
In this scenario:
When the Character device is still open, if you operate the device
through configfs and execute commands like unlink, the resources
allocated when the device is bound will be released(printer_dev). After
that, if you perform ioctl operation again, it will appear
use-after-free. add kref to show that this resource(printer_dev) will
also use,
until this character device is close.
Similar problems can occur in f_hid.c.
As for the other gadget drivers, I haven't seen their logical
implementation,so I'm not sure
thanks,
Zqiang
On 6/18/20 4:30 PM, Greg KH wrote:
> On Fri, Jun 05, 2020 at 11:56:52AM +0800, [email protected] wrote:
>> From: Zqiang <[email protected]>
>>
>> Fix this by increase object reference count.
>>
>> BUG: KASAN: use-after-free in __lock_acquire+0x3fd4/0x4180
>> kernel/locking/lockdep.c:3831
>> Read of size 8 at addr ffff8880683b0018 by task syz-executor.0/3377
>>
>> CPU: 1 PID: 3377 Comm: syz-executor.0 Not tainted 5.6.11 #1
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> Call Trace:
>> __dump_stack lib/dump_stack.c:77 [inline]
>> dump_stack+0xce/0x128 lib/dump_stack.c:118
>> print_address_description.constprop.4+0x21/0x3c0 mm/kasan/report.c:374
>> __kasan_report+0x131/0x1b0 mm/kasan/report.c:506
>> kasan_report+0x12/0x20 mm/kasan/common.c:641
>> __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
>> __lock_acquire+0x3fd4/0x4180 kernel/locking/lockdep.c:3831
>> lock_acquire+0x127/0x350 kernel/locking/lockdep.c:4488
>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>> _raw_spin_lock_irqsave+0x35/0x50 kernel/locking/spinlock.c:159
>> printer_ioctl+0x4a/0x110 drivers/usb/gadget/function/f_printer.c:723
>> vfs_ioctl fs/ioctl.c:47 [inline]
>> ksys_ioctl+0xfb/0x130 fs/ioctl.c:763
>> __do_sys_ioctl fs/ioctl.c:772 [inline]
>> __se_sys_ioctl fs/ioctl.c:770 [inline]
>> __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:770
>> do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> RIP: 0033:0x4531a9
>> Code: ed 60 fc ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48
>> 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
>> 01 f0 ff ff 0f 83 bb 60 fc ff c3 66 2e 0f 1f 84 00 00 00 00
>> RSP: 002b:00007fd14ad72c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 000000000073bfa8 RCX: 00000000004531a9
>> RDX: fffffffffffffff9 RSI: 000000000000009e RDI: 0000000000000003
>> RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004bbd61
>> R13: 00000000004d0a98 R14: 00007fd14ad736d4 R15: 00000000ffffffff
>>
>> Allocated by task 2393:
>> save_stack+0x21/0x90 mm/kasan/common.c:72
>> set_track mm/kasan/common.c:80 [inline]
>> __kasan_kmalloc.constprop.3+0xa7/0xd0 mm/kasan/common.c:515
>> kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
>> kmem_cache_alloc_trace+0xfa/0x2d0 mm/slub.c:2813
>> kmalloc include/linux/slab.h:555 [inline]
>> kzalloc include/linux/slab.h:669 [inline]
>> gprinter_alloc+0xa1/0x870 drivers/usb/gadget/function/f_printer.c:1416
>> usb_get_function+0x58/0xc0 drivers/usb/gadget/functions.c:61
>> config_usb_cfg_link+0x1ed/0x3e0 drivers/usb/gadget/configfs.c:444
>> configfs_symlink+0x527/0x11d0 fs/configfs/symlink.c:202
>> vfs_symlink+0x33d/0x5b0 fs/namei.c:4201
>> do_symlinkat+0x11b/0x1d0 fs/namei.c:4228
>> __do_sys_symlinkat fs/namei.c:4242 [inline]
>> __se_sys_symlinkat fs/namei.c:4239 [inline]
>> __x64_sys_symlinkat+0x73/0xb0 fs/namei.c:4239
>> do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> Freed by task 3368:
>> save_stack+0x21/0x90 mm/kasan/common.c:72
>> set_track mm/kasan/common.c:80 [inline]
>> kasan_set_free_info mm/kasan/common.c:337 [inline]
>> __kasan_slab_free+0x135/0x190 mm/kasan/common.c:476
>> kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
>> slab_free_hook mm/slub.c:1444 [inline]
>> slab_free_freelist_hook mm/slub.c:1477 [inline]
>> slab_free mm/slub.c:3034 [inline]
>> kfree+0xf7/0x410 mm/slub.c:3995
>> gprinter_free+0x49/0xd0 drivers/usb/gadget/function/f_printer.c:1353
>> usb_put_function+0x38/0x50 drivers/usb/gadget/functions.c:87
>> config_usb_cfg_unlink+0x2db/0x3b0 drivers/usb/gadget/configfs.c:485
>> configfs_unlink+0x3b9/0x7f0 fs/configfs/symlink.c:250
>> vfs_unlink+0x287/0x570 fs/namei.c:4073
>> do_unlinkat+0x4f9/0x620 fs/namei.c:4137
>> __do_sys_unlink fs/namei.c:4184 [inline]
>> __se_sys_unlink fs/namei.c:4182 [inline]
>> __x64_sys_unlink+0x42/0x50 fs/namei.c:4182
>> do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> The buggy address belongs to the object at ffff8880683b0000
>> which belongs to the cache kmalloc-1k of size 1024
>> The buggy address is located 24 bytes inside of
>> 1024-byte region [ffff8880683b0000, ffff8880683b0400)
>> The buggy address belongs to the page:
>> page:ffffea0001a0ec00 refcount:1 mapcount:0 mapping:ffff88806c00e300
>> index:0xffff8880683b1800 compound_mapcount: 0
>> flags: 0x100000000010200(slab|head)
>> raw: 0100000000010200 0000000000000000 0000000600000001 ffff88806c00e300
>> raw: ffff8880683b1800 000000008010000a 00000001ffffffff 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Reported-by: Kyungtae Kim <[email protected]>
>> Signed-off-by: Zqiang <[email protected]>
>> ---
>> drivers/usb/gadget/function/f_printer.c | 16 ++++++++++++++--
>> 1 file changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
>> index 9c7ed2539ff7..8ed1295d7e35 100644
>> --- a/drivers/usb/gadget/function/f_printer.c
>> +++ b/drivers/usb/gadget/function/f_printer.c
>> @@ -31,6 +31,7 @@
>> #include <linux/types.h>
>> #include <linux/ctype.h>
>> #include <linux/cdev.h>
>> +#include <linux/kref.h>
>>
>> #include <asm/byteorder.h>
>> #include <linux/io.h>
>> @@ -64,7 +65,7 @@ struct printer_dev {
>> struct usb_gadget *gadget;
>> s8 interface;
>> struct usb_ep *in_ep, *out_ep;
>> -
>> + struct kref kref;
>> struct list_head rx_reqs; /* List of free RX structs */
>> struct list_head rx_reqs_active; /* List of Active RX xfers */
>> struct list_head rx_buffers; /* List of completed xfers */
>
> Isn't there already a reference count for this structure? Why not use
> that instead?
>
> If not, should this be done to all gadget drivers? What makes this one
> unique?
>
> thanks,
>
> greg k-h
>