Re: [PATCH v4.14] usb: gadget: f_fs: Fix setting of device and driver data cross-references

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sun, Jul 11, 2021 at 10:51:30AM -0500, Andrew Gabbasov wrote:
> commit ecfbd7b9054bddb12cea07fda41bb3a79a7b0149 upstream.
> 
> FunctionFS device structure 'struct ffs_dev' and driver data structure
> 'struct ffs_data' are bound to each other with cross-reference pointers
> 'ffs_data->private_data' and 'ffs_dev->ffs_data'. While the first one
> is supposed to be valid through the whole life of 'struct ffs_data'
> (and while 'struct ffs_dev' exists non-freed), the second one is cleared
> in 'ffs_closed()' (called from 'ffs_data_reset()' or the last
> 'ffs_data_put()'). This can be called several times, alternating in
> different order with 'ffs_free_inst()', that, if possible, clears
> the other cross-reference.
> 
> As a result, different cases of these calls order may leave stale
> cross-reference pointers, used when the pointed structure is already
> freed. Even if it occasionally doesn't cause kernel crash, this error
> is reported by KASAN-enabled kernel configuration.
> 
> For example, the case [last 'ffs_data_put()' - 'ffs_free_inst()'] was
> fixed by commit cdafb6d8b8da ("usb: gadget: f_fs: Fix use-after-free in
> ffs_free_inst").
> 
> The other case ['ffs_data_reset()' - 'ffs_free_inst()' - 'ffs_data_put()']
> now causes KASAN reported error [1], when 'ffs_data_reset()' clears
> 'ffs_dev->ffs_data', then 'ffs_free_inst()' frees the 'struct ffs_dev',
> but can't clear 'ffs_data->private_data', which is then accessed
> in 'ffs_closed()' called from 'ffs_data_put()'. This happens since
> 'ffs_dev->ffs_data' reference is cleared too early.
> 
> Moreover, one more use case, when 'ffs_free_inst()' is called immediately
> after mounting FunctionFS device (that is before the descriptors are
> written and 'ffs_ready()' is called), and then 'ffs_data_reset()'
> or 'ffs_data_put()' is called from accessing "ep0" file or unmounting
> the device. This causes KASAN error report like [2], since
> 'ffs_dev->ffs_data' is not yet set when 'ffs_free_inst()' can't properly
> clear 'ffs_data->private_data', that is later accessed to freed structure.
> 
> Fix these (and may be other) cases of stale pointers access by moving
> setting and clearing of the mentioned cross-references to the single
> places, setting both of them when 'struct ffs_data' is created and
> bound to 'struct ffs_dev', and clearing both of them when one of the
> structures is destroyed. It seems convenient to make this pointer
> initialization and structures binding in 'ffs_acquire_dev()' and
> make pointers clearing in 'ffs_release_dev()'. This required some
> changes in these functions parameters and return types.
> 
> Also, 'ffs_release_dev()' calling requires some cleanup, fixing minor
> issues, like (1) 'ffs_release_dev()' is not called if 'ffs_free_inst()'
> is called without unmounting the device, and "release_dev" callback
> is not called at all, or (2) "release_dev" callback is called before
> "ffs_closed" callback on unmounting, which seems to be not correctly
> nested with "acquire_dev" and "ffs_ready" callbacks.
> Make this cleanup togther with other mentioned 'ffs_release_dev()' changes.
> 
> [1]
> ==================================================================
> root@rcar-gen3:~# mkdir /dev/cfs
> root@rcar-gen3:~# mkdir /dev/ffs
> root@rcar-gen3:~# modprobe libcomposite
> root@rcar-gen3:~# mount -t configfs none /dev/cfs
> root@rcar-gen3:~# mkdir /dev/cfs/usb_gadget/g1
> root@rcar-gen3:~# mkdir /dev/cfs/usb_gadget/g1/functions/ffs.ffs
> [   64.340664] file system registered
> root@rcar-gen3:~# mount -t functionfs ffs /dev/ffs
> root@rcar-gen3:~# cd /dev/ffs
> root@rcar-gen3:/dev/ffs# /home/root/ffs-test
> ffs-test: info: ep0: writing descriptors (in v2 format)
> [   83.181442] read descriptors
> [   83.186085] read strings
> ffs-test: info: ep0: writing strings
> ffs-test: dbg:  ep1: starting
> ffs-test: dbg:  ep2: starting
> ffs-test: info: ep1: starts
> ffs-test: info: ep2: starts
> ffs-test: info: ep0: starts
> 
> ^C
> root@rcar-gen3:/dev/ffs# cd /home/root/
> root@rcar-gen3:~# rmdir /dev/cfs/usb_gadget/g1/functions/ffs.ffs
> [   98.935061] unloading
> root@rcar-gen3:~# umount /dev/ffs
> [  102.734301] ==================================================================
> [  102.742059] BUG: KASAN: use-after-free in ffs_release_dev+0x64/0xa8 [usb_f_fs]
> [  102.749683] Write of size 1 at addr ffff0004d46ff549 by task umount/2997
> [  102.756709]
> [  102.758311] CPU: 0 PID: 2997 Comm: umount Not tainted 5.13.0-rc4+ #8
> [  102.764971] Hardware name: Renesas Salvator-X board based on r8a77951 (DT)
> [  102.772179] Call trace:
> [  102.774779]  dump_backtrace+0x0/0x330
> [  102.778653]  show_stack+0x20/0x2c
> [  102.782152]  dump_stack+0x11c/0x1ac
> [  102.785833]  print_address_description.constprop.0+0x30/0x274
> [  102.791862]  kasan_report+0x14c/0x1c8
> [  102.795719]  __asan_report_store1_noabort+0x34/0x58
> [  102.800840]  ffs_release_dev+0x64/0xa8 [usb_f_fs]
> [  102.805801]  ffs_fs_kill_sb+0x50/0x84 [usb_f_fs]
> [  102.810663]  deactivate_locked_super+0xa0/0xf0
> [  102.815339]  deactivate_super+0x98/0xac
> [  102.819378]  cleanup_mnt+0xd0/0x1b0
> [  102.823057]  __cleanup_mnt+0x1c/0x28
> [  102.826823]  task_work_run+0x104/0x180
> [  102.830774]  do_notify_resume+0x458/0x14e0
> [  102.835083]  work_pending+0xc/0x5f8
> [  102.838762]
> [  102.840357] Allocated by task 2988:
> [  102.844032]  kasan_save_stack+0x28/0x58
> [  102.848071]  kasan_set_track+0x28/0x3c
> [  102.852016]  ____kasan_kmalloc+0x84/0x9c
> [  102.856142]  __kasan_kmalloc+0x10/0x1c
> [  102.860088]  __kmalloc+0x214/0x2f8
> [  102.863678]  kzalloc.constprop.0+0x14/0x20 [usb_f_fs]
> [  102.868990]  ffs_alloc_inst+0x8c/0x208 [usb_f_fs]
> [  102.873942]  try_get_usb_function_instance+0xf0/0x164 [libcomposite]
> [  102.880629]  usb_get_function_instance+0x64/0x68 [libcomposite]
> [  102.886858]  function_make+0x128/0x1ec [libcomposite]
> [  102.892185]  configfs_mkdir+0x330/0x590 [configfs]
> [  102.897245]  vfs_mkdir+0x12c/0x1bc
> [  102.900835]  do_mkdirat+0x180/0x1d0
> [  102.904513]  __arm64_sys_mkdirat+0x80/0x94
> [  102.908822]  invoke_syscall+0xf8/0x25c
> [  102.912772]  el0_svc_common.constprop.0+0x150/0x1a0
> [  102.917891]  do_el0_svc+0xa0/0xd4
> [  102.921386]  el0_svc+0x24/0x34
> [  102.924613]  el0_sync_handler+0xcc/0x154
> [  102.928743]  el0_sync+0x198/0x1c0
> [  102.932238]
> [  102.933832] Freed by task 2996:
> [  102.937144]  kasan_save_stack+0x28/0x58
> [  102.941181]  kasan_set_track+0x28/0x3c
> [  102.945128]  kasan_set_free_info+0x28/0x4c
> [  102.949435]  ____kasan_slab_free+0x104/0x118
> [  102.953921]  __kasan_slab_free+0x18/0x24
> [  102.958047]  slab_free_freelist_hook+0x148/0x1f0
> [  102.962897]  kfree+0x318/0x440
> [  102.966123]  ffs_free_inst+0x164/0x2d8 [usb_f_fs]
> [  102.971075]  usb_put_function_instance+0x84/0xa4 [libcomposite]
> [  102.977302]  ffs_attr_release+0x18/0x24 [usb_f_fs]
> [  102.982344]  config_item_put+0x140/0x1a4 [configfs]
> [  102.987486]  configfs_rmdir+0x3fc/0x518 [configfs]
> [  102.992535]  vfs_rmdir+0x114/0x234
> [  102.996122]  do_rmdir+0x274/0x2b0
> [  102.999617]  __arm64_sys_unlinkat+0x94/0xc8
> [  103.004015]  invoke_syscall+0xf8/0x25c
> [  103.007961]  el0_svc_common.constprop.0+0x150/0x1a0
> [  103.013080]  do_el0_svc+0xa0/0xd4
> [  103.016575]  el0_svc+0x24/0x34
> [  103.019801]  el0_sync_handler+0xcc/0x154
> [  103.023930]  el0_sync+0x198/0x1c0
> [  103.027426]
> [  103.029020] The buggy address belongs to the object at ffff0004d46ff500
> [  103.029020]  which belongs to the cache kmalloc-128 of size 128
> [  103.042079] The buggy address is located 73 bytes inside of
> [  103.042079]  128-byte region [ffff0004d46ff500, ffff0004d46ff580)
> [  103.054236] The buggy address belongs to the page:
> [  103.059262] page:0000000021aa849b refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff0004d46fee00 pfn:0x5146fe
> [  103.070437] head:0000000021aa849b order:1 compound_mapcount:0
> [  103.076456] flags: 0x8000000000010200(slab|head|zone=2)
> [  103.081948] raw: 8000000000010200 fffffc0013521a80 0000000d0000000d ffff0004c0002300
> [  103.090052] raw: ffff0004d46fee00 000000008020001e 00000001ffffffff 0000000000000000
> [  103.098150] page dumped because: kasan: bad access detected
> [  103.103985]
> [  103.105578] Memory state around the buggy address:
> [  103.110602]  ffff0004d46ff400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  103.118161]  ffff0004d46ff480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  103.125726] >ffff0004d46ff500: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  103.133284]                                               ^
> [  103.139120]  ffff0004d46ff580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  103.146679]  ffff0004d46ff600: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  103.154238] ==================================================================
> [  103.161792] Disabling lock debugging due to kernel taint
> [  103.167319] Unable to handle kernel paging request at virtual address 0037801d6000018e
> [  103.175406] Mem abort info:
> [  103.178457]   ESR = 0x96000004
> [  103.181609]   EC = 0x25: DABT (current EL), IL = 32 bits
> [  103.187020]   SET = 0, FnV = 0
> [  103.190185]   EA = 0, S1PTW = 0
> [  103.193417] Data abort info:
> [  103.196385]   ISV = 0, ISS = 0x00000004
> [  103.200315]   CM = 0, WnR = 0
> [  103.203366] [0037801d6000018e] address between user and kernel address ranges
> [  103.210611] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [  103.216231] Modules linked in: usb_f_fs libcomposite configfs ath9k_htc led_class mac80211 libarc4 ath9k_common ath9k_hw ath cfg80211 aes_ce_blk sata_rc4
> [  103.259233] CPU: 0 PID: 2997 Comm: umount Tainted: G    B             5.13.0-rc4+ #8
> [  103.267031] Hardware name: Renesas Salvator-X board based on r8a77951 (DT)
> [  103.273951] pstate: 00000005 (nzcv daif -PAN -UAO -TCO BTYPE=--)
> [  103.280001] pc : ffs_data_clear+0x138/0x370 [usb_f_fs]
> [  103.285197] lr : ffs_data_clear+0x124/0x370 [usb_f_fs]
> [  103.290385] sp : ffff800014777a80
> [  103.293725] x29: ffff800014777a80 x28: ffff0004d7649c80 x27: 0000000000000000
> [  103.300931] x26: ffff800014777fb0 x25: ffff60009aec9394 x24: ffff0004d7649ca4
> [  103.308136] x23: 1fffe0009a3d063a x22: dfff800000000000 x21: ffff0004d1e831d0
> [  103.315340] x20: e1c000eb00000bb4 x19: ffff0004d1e83000 x18: 0000000000000000
> [  103.322545] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
> [  103.329748] x14: 0720072007200720 x13: 0720072007200720 x12: 1ffff000012ef658
> [  103.336952] x11: ffff7000012ef658 x10: 0720072007200720 x9 : ffff800011322648
> [  103.344157] x8 : ffff800014777818 x7 : ffff80000977b2c7 x6 : 0000000000000000
> [  103.351359] x5 : 0000000000000001 x4 : ffff7000012ef659 x3 : 0000000000000001
> [  103.358562] x2 : 0000000000000000 x1 : 1c38001d6000018e x0 : e1c000eb00000c70
> [  103.365766] Call trace:
> [  103.368235]  ffs_data_clear+0x138/0x370 [usb_f_fs]
> [  103.373076]  ffs_data_reset+0x20/0x304 [usb_f_fs]
> [  103.377829]  ffs_data_closed+0x1ec/0x244 [usb_f_fs]
> [  103.382755]  ffs_fs_kill_sb+0x70/0x84 [usb_f_fs]
> [  103.387420]  deactivate_locked_super+0xa0/0xf0
> [  103.391905]  deactivate_super+0x98/0xac
> [  103.395776]  cleanup_mnt+0xd0/0x1b0
> [  103.399299]  __cleanup_mnt+0x1c/0x28
> [  103.402906]  task_work_run+0x104/0x180
> [  103.406691]  do_notify_resume+0x458/0x14e0
> [  103.410823]  work_pending+0xc/0x5f8
> [  103.414351] Code: b4000a54 9102f280 12000802 d343fc01 (38f66821)
> [  103.420490] ---[ end trace 57b43a50e8244f57 ]---
> Segmentation fault
> root@rcar-gen3:~#
> ==================================================================
> 
> [2]
> ==================================================================
> root@rcar-gen3:~# mkdir /dev/ffs
> root@rcar-gen3:~# modprobe libcomposite
> root@rcar-gen3:~#
> root@rcar-gen3:~# mount -t configfs none /dev/cfs
> root@rcar-gen3:~# mkdir /dev/cfs/usb_gadget/g1
> root@rcar-gen3:~# mkdir /dev/cfs/usb_gadget/g1/functions/ffs.ffs
> [   54.766480] file system registered
> root@rcar-gen3:~# mount -t functionfs ffs /dev/ffs
> root@rcar-gen3:~# rmdir /dev/cfs/usb_gadget/g1/functions/ffs.ffs
> [   63.197597] unloading
> root@rcar-gen3:~# cat /dev/ffs/ep0
> cat: read error:[   67.213506] ==================================================================
> [   67.222095] BUG: KASAN: use-after-free in ffs_data_clear+0x70/0x370 [usb_f_fs]
> [   67.229699] Write of size 1 at addr ffff0004c26e974a by task cat/2994
> [   67.236446]
> [   67.238045] CPU: 0 PID: 2994 Comm: cat Not tainted 5.13.0-rc4+ #8
> [   67.244431] Hardware name: Renesas Salvator-X board based on r8a77951 (DT)
> [   67.251624] Call trace:
> [   67.254212]  dump_backtrace+0x0/0x330
> [   67.258081]  show_stack+0x20/0x2c
> [   67.261579]  dump_stack+0x11c/0x1ac
> [   67.265260]  print_address_description.constprop.0+0x30/0x274
> [   67.271286]  kasan_report+0x14c/0x1c8
> [   67.275143]  __asan_report_store1_noabort+0x34/0x58
> [   67.280265]  ffs_data_clear+0x70/0x370 [usb_f_fs]
> [   67.285220]  ffs_data_reset+0x20/0x304 [usb_f_fs]
> [   67.290172]  ffs_data_closed+0x240/0x244 [usb_f_fs]
> [   67.295305]  ffs_ep0_release+0x40/0x54 [usb_f_fs]
> [   67.300256]  __fput+0x304/0x580
> [   67.303576]  ____fput+0x18/0x24
> [   67.306893]  task_work_run+0x104/0x180
> [   67.310846]  do_notify_resume+0x458/0x14e0
> [   67.315154]  work_pending+0xc/0x5f8
> [   67.318834]
> [   67.320429] Allocated by task 2988:
> [   67.324105]  kasan_save_stack+0x28/0x58
> [   67.328144]  kasan_set_track+0x28/0x3c
> [   67.332090]  ____kasan_kmalloc+0x84/0x9c
> [   67.336217]  __kasan_kmalloc+0x10/0x1c
> [   67.340163]  __kmalloc+0x214/0x2f8
> [   67.343754]  kzalloc.constprop.0+0x14/0x20 [usb_f_fs]
> [   67.349066]  ffs_alloc_inst+0x8c/0x208 [usb_f_fs]
> [   67.354017]  try_get_usb_function_instance+0xf0/0x164 [libcomposite]
> [   67.360705]  usb_get_function_instance+0x64/0x68 [libcomposite]
> [   67.366934]  function_make+0x128/0x1ec [libcomposite]
> [   67.372260]  configfs_mkdir+0x330/0x590 [configfs]
> [   67.377320]  vfs_mkdir+0x12c/0x1bc
> [   67.380911]  do_mkdirat+0x180/0x1d0
> [   67.384589]  __arm64_sys_mkdirat+0x80/0x94
> [   67.388899]  invoke_syscall+0xf8/0x25c
> [   67.392850]  el0_svc_common.constprop.0+0x150/0x1a0
> [   67.397969]  do_el0_svc+0xa0/0xd4
> [   67.401464]  el0_svc+0x24/0x34
> [   67.404691]  el0_sync_handler+0xcc/0x154
> [   67.408819]  el0_sync+0x198/0x1c0
> [   67.412315]
> [   67.413909] Freed by task 2993:
> [   67.417220]  kasan_save_stack+0x28/0x58
> [   67.421257]  kasan_set_track+0x28/0x3c
> [   67.425204]  kasan_set_free_info+0x28/0x4c
> [   67.429513]  ____kasan_slab_free+0x104/0x118
> [   67.434001]  __kasan_slab_free+0x18/0x24
> [   67.438128]  slab_free_freelist_hook+0x148/0x1f0
> [   67.442978]  kfree+0x318/0x440
> [   67.446205]  ffs_free_inst+0x164/0x2d8 [usb_f_fs]
> [   67.451156]  usb_put_function_instance+0x84/0xa4 [libcomposite]
> [   67.457385]  ffs_attr_release+0x18/0x24 [usb_f_fs]
> [   67.462428]  config_item_put+0x140/0x1a4 [configfs]
> [   67.467570]  configfs_rmdir+0x3fc/0x518 [configfs]
> [   67.472626]  vfs_rmdir+0x114/0x234
> [   67.476215]  do_rmdir+0x274/0x2b0
> [   67.479710]  __arm64_sys_unlinkat+0x94/0xc8
> [   67.484108]  invoke_syscall+0xf8/0x25c
> [   67.488055]  el0_svc_common.constprop.0+0x150/0x1a0
> [   67.493175]  do_el0_svc+0xa0/0xd4
> [   67.496671]  el0_svc+0x24/0x34
> [   67.499896]  el0_sync_handler+0xcc/0x154
> [   67.504024]  el0_sync+0x198/0x1c0
> [   67.507520]
> [   67.509114] The buggy address belongs to the object at ffff0004c26e9700
> [   67.509114]  which belongs to the cache kmalloc-128 of size 128
> [   67.522171] The buggy address is located 74 bytes inside of
> [   67.522171]  128-byte region [ffff0004c26e9700, ffff0004c26e9780)
> [   67.534328] The buggy address belongs to the page:
> [   67.539355] page:000000003177a217 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5026e8
> [   67.549175] head:000000003177a217 order:1 compound_mapcount:0
> [   67.555195] flags: 0x8000000000010200(slab|head|zone=2)
> [   67.560687] raw: 8000000000010200 fffffc0013037100 0000000c00000002 ffff0004c0002300
> [   67.568791] raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
> [   67.576890] page dumped because: kasan: bad access detected
> [   67.582725]
> [   67.584318] Memory state around the buggy address:
> [   67.589343]  ffff0004c26e9600: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [   67.596903]  ffff0004c26e9680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [   67.604463] >ffff0004c26e9700: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [   67.612022]                                               ^
> [   67.617860]  ffff0004c26e9780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [   67.625421]  ffff0004c26e9800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [   67.632981] ==================================================================
> [   67.640535] Disabling lock debugging due to kernel taint
>  File descriptor[   67.646100] Unable to handle kernel paging request at virtual address fabb801d4000018d
>  in bad state
> [   67.655456] Mem abort info:
> [   67.659619]   ESR = 0x96000004
> [   67.662801]   EC = 0x25: DABT (current EL), IL = 32 bits
> [   67.668225]   SET = 0, FnV = 0
> [   67.671375]   EA = 0, S1PTW = 0
> [   67.674613] Data abort info:
> [   67.677587]   ISV = 0, ISS = 0x00000004
> [   67.681522]   CM = 0, WnR = 0
> [   67.684588] [fabb801d4000018d] address between user and kernel address ranges
> [   67.691849] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [   67.697470] Modules linked in: usb_f_fs libcomposite configfs ath9k_htc led_class mac80211 libarc4 ath9k_common ath9k_hw ath cfg80211 aes_ce_blk crypto_simd cryptd aes_ce_cipher ghash_ce gf128mul sha2_ce sha1_ce evdev sata_rcar libata xhci_plat_hcd scsi_mod xhci_hcd rene4
> [   67.740467] CPU: 0 PID: 2994 Comm: cat Tainted: G    B             5.13.0-rc4+ #8
> [   67.748005] Hardware name: Renesas Salvator-X board based on r8a77951 (DT)
> [   67.754924] pstate: 00000005 (nzcv daif -PAN -UAO -TCO BTYPE=--)
> [   67.760974] pc : ffs_data_clear+0x138/0x370 [usb_f_fs]
> [   67.766178] lr : ffs_data_clear+0x124/0x370 [usb_f_fs]
> [   67.771365] sp : ffff800014767ad0
> [   67.774706] x29: ffff800014767ad0 x28: ffff800009cf91c0 x27: ffff0004c54861a0
> [   67.781913] x26: ffff0004dc90b288 x25: 1fffe00099ec10f5 x24: 00000000000a801d
> [   67.789118] x23: 1fffe00099f6953a x22: dfff800000000000 x21: ffff0004cfb4a9d0
> [   67.796322] x20: d5e000ea00000bb1 x19: ffff0004cfb4a800 x18: 0000000000000000
> [   67.803526] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
> [   67.810730] x14: 0720072007200720 x13: 0720072007200720 x12: 1ffff000028ecefa
> [   67.817934] x11: ffff7000028ecefa x10: 0720072007200720 x9 : ffff80001132c014
> [   67.825137] x8 : ffff8000147677d8 x7 : ffff8000147677d7 x6 : 0000000000000000
> [   67.832341] x5 : 0000000000000001 x4 : ffff7000028ecefb x3 : 0000000000000001
> [   67.839544] x2 : 0000000000000005 x1 : 1abc001d4000018d x0 : d5e000ea00000c6d
> [   67.846748] Call trace:
> [   67.849218]  ffs_data_clear+0x138/0x370 [usb_f_fs]
> [   67.854058]  ffs_data_reset+0x20/0x304 [usb_f_fs]
> [   67.858810]  ffs_data_closed+0x240/0x244 [usb_f_fs]
> [   67.863736]  ffs_ep0_release+0x40/0x54 [usb_f_fs]
> [   67.868488]  __fput+0x304/0x580
> [   67.871665]  ____fput+0x18/0x24
> [   67.874837]  task_work_run+0x104/0x180
> [   67.878622]  do_notify_resume+0x458/0x14e0
> [   67.882754]  work_pending+0xc/0x5f8
> [   67.886282] Code: b4000a54 9102f280 12000802 d343fc01 (38f66821)
> [   67.892422] ---[ end trace 6d7cedf53d7abbea ]---
> Segmentation fault
> root@rcar-gen3:~#
> ==================================================================
> 
> Fixes: 4b187fceec3c ("usb: gadget: FunctionFS: add devices management code")
> Fixes: 3262ad824307 ("usb: gadget: f_fs: Stop ffs_closed NULL pointer dereference")
> Fixes: cdafb6d8b8da ("usb: gadget: f_fs: Fix use-after-free in ffs_free_inst")
> Reported-by: Bhuvanesh Surachari <bhuvanesh_surachari@mentor.com>
> Tested-by: Eugeniu Rosca <erosca@de.adit-jv.com>
> Reviewed-by: Eugeniu Rosca <erosca@de.adit-jv.com>
> Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
> Link: https://lore.kernel.org/r/20210603171507.22514-1-andrew_gabbasov@mentor.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> [agabbasov: Backported to earlier mount API, resolved context conflicts]
> ---
>  drivers/usb/gadget/function/f_fs.c | 67 ++++++++++++++----------------
>  1 file changed, 32 insertions(+), 35 deletions(-)

I also need a 4.19 version of this commit, as you do not want to upgrade
to a newer kernel and regress.  Can you also provide that?

thanks,

greg k-h