Re: [PATCH] usb: gadget: function: printer: fix use-after-free in __lock_acquire

[Greg KH]

On Fri, Jun 05, 2020 at 11:56:52AM +0800, qiang.zhang@xxxxxxxxxxxxx wrote:
> From: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
> 
> 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 <kt0755@xxxxxxxxx>
> Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
> ---
>  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