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

Greg Kroah-Hartman
2021-07-11T16:07:35Z

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