Re: KASAN: use-after-free Read in printer_read

[Greg KH]

On Tue, Jun 02, 2020 at 04:35:33PM -0400, Kyungtae Kim wrote:
> We report a bug (in linux-5.6.11) found by FuzzUSB (a modified version
> of syzkaller)
> 
> This bug happened when accessing a deallocated instance in printer_read().
> 
> printer_read() tries to access lock_printer_io of the printer_dev instance
> (f_printer.c:430). However, UAF arises because it had been freed
> by gprinter_free().
> 
> To fix, we can check if an instance of printer_dev is still in use
> before deallocating it.
> 
> kernel config: https://kt0755.github.io/etc/config_v5.6.11
> 
> ==================================================================
> BUG: KASAN: use-after-free in __mutex_lock_common
> kernel/locking/mutex.c:938 [inline]
> BUG: KASAN: use-after-free in __mutex_lock+0x13a7/0x14d0
> kernel/locking/mutex.c:1103
> Read of size 8 at addr ffff8880540c3890 by task syz-executor.0/6819
> 
> CPU: 1 PID: 6819 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
>  __mutex_lock_common kernel/locking/mutex.c:938 [inline]
>  __mutex_lock+0x13a7/0x14d0 kernel/locking/mutex.c:1103
>  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118
>  printer_read+0xbc/0xd60 drivers/usb/gadget/function/f_printer.c:430
>  __vfs_read+0x85/0x110 fs/read_write.c:425
>  vfs_read+0x161/0x380 fs/read_write.c:461
>  ksys_read+0x18a/0x220 fs/read_write.c:587
>  __do_sys_read fs/read_write.c:597 [inline]
>  __se_sys_read fs/read_write.c:595 [inline]
>  __x64_sys_read+0x73/0xb0 fs/read_write.c:595
>  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:00007f0024694c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 000000000073bfa8 RCX: 00000000004531a9
> RDX: 000000000000006b RSI: 0000000020000100 RDI: 0000000000000003
> RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004bd843
> R13: 00000000004d3468 R14: 00007f00246956d4 R15: 00000000ffffffff
> 
> Allocated by task 2420:
>  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 6798:
>  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 ffff8880540c3800
>  which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 144 bytes inside of
>  1024-byte region [ffff8880540c3800, ffff8880540c3c00)
> The buggy address belongs to the page:
> page:ffffea0001503000 refcount:1 mapcount:0 mapping:ffff88806c00e300
> index:0xffff8880540c4800 compound_mapcount: 0
> flags: 0x100000000010200(slab|head)
> raw: 0100000000010200 ffffea0001ae3808 ffffea0001ac6c08 ffff88806c00e300
> raw: ffff8880540c4800 0000000000100007 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880540c3780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8880540c3800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff8880540c3880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                          ^
>  ffff8880540c3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880540c3980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

Can you send a patch to fix this so that you get full credit for
finding, and fixing the issue?

thanks,

greg k-h