If usb_ep_autoconfig() fails (i.e. returns a null endpoint descriptor),
we expect afunc_bind() to fail (i.e. return a negative error code).

However, due to v4.10-rc1 commit f1d3861d ("usb: gadget: f_uac2: fix
error handling at afunc_bind"), afunc_bind() returns zero, telling the
caller that it succeeded. This then generates NULL pointer dereference
in below scenario on Rcar H3-ES20-Salvator-X target:

rcar-gen3:/home/root# modprobe g_audio
[  626.521155] g_audio gadget: afunc_bind:565 Error!
[  626.526319] g_audio gadget: Linux USB Audio Gadget, version: Feb 2, 2012
[  626.533405] g_audio gadget: g_audio ready
rcar-gen3:/home/root#
rcar-gen3:/home/root# modprobe -r g_audio
[  728.256707] ==================================================================
[  728.264293] BUG: KASAN: null-ptr-deref in u_audio_stop_capture+0x70/0x268 [u_audio]
[  728.272244] Read of size 8 at addr 00000000000000a0 by task modprobe/2545
[  728.279309]
[  728.280849] CPU: 0 PID: 2545 Comm: modprobe Tainted: G        WC      4.14.47+ #152
[  728.288778] Hardware name: Renesas Salvator-X board based on r8a7795 ES2.0+ (DT)
[  728.296454] Call trace:
[  728.299151] [<ffff2000080925ac>] dump_backtrace+0x0/0x364
[  728.304808] [<ffff200008092924>] show_stack+0x14/0x1c
[  728.310081] [<ffff200008f8d5cc>] dump_stack+0x108/0x174
[  728.315522] [<ffff2000083c77c8>] kasan_report+0x1fc/0x354
[  728.321134] [<ffff2000083c611c>] __asan_load8+0x24/0x94
[  728.326600] [<ffff2000021e1618>] u_audio_stop_capture+0x70/0x268 [u_audio]
[  728.333735] [<ffff2000021f8b7c>] afunc_disable+0x44/0x60 [usb_f_uac2]
[  728.340503] [<ffff20000218177c>] usb_remove_function+0x9c/0x210 [libcomposite]
[  728.348060] [<ffff200002183320>] remove_config.isra.2+0x1d8/0x218 [libcomposite]
[  728.355788] [<ffff200002186c54>] __composite_unbind+0x104/0x1f8 [libcomposite]
[  728.363339] [<ffff200002186d58>] composite_unbind+0x10/0x18 [libcomposite]
[  728.370536] [<ffff20000152f158>] usb_gadget_remove_driver+0xc0/0x170 [udc_core]
[  728.378172] [<ffff20000153154c>] usb_gadget_unregister_driver+0x1cc/0x258 [udc_core]
[  728.386274] [<ffff200002180de8>] usb_composite_unregister+0x10/0x18 [libcomposite]
[  728.394116] [<ffff2000021d035c>] audio_driver_exit+0x14/0x28 [g_audio]
[  728.400878] [<ffff200008213ed4>] SyS_delete_module+0x288/0x32c
[  728.406935] Exception stack(0xffff8006cf6c7ec0 to 0xffff8006cf6c8000)
[  728.413624] 7ec0: 0000000006136428 0000000000000800 0000000000000000 0000ffffd706efe8
[  728.421718] 7ee0: 0000ffffd706efe9 000000000000000a 1999999999999999 0000000000000000
[  728.429792] 7f00: 000000000000006a 000000000042c078 0000000000000000 0000000000000005
[  728.437870] 7f20: 0000000000000000 0000000000000000 0000000000000004 0000000000000000
[  728.445952] 7f40: 000000000042bfc8 0000ffffbc7c8f40 0000000000000000 00000000061363c0
[  728.454035] 7f60: 0000000006136428 0000000000000000 0000000000000000 0000000006136428
[  728.462114] 7f80: 000000000042c000 0000ffffd7071448 000000000042c000 0000000000000000
[  728.470190] 7fa0: 00000000061350c0 0000ffffd7070010 000000000041129c 0000ffffd7070010
[  728.478281] 7fc0: 0000ffffbc7c8f48 0000000060000000 0000000006136428 000000000000006a
[  728.486351] 7fe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[  728.494434] [<ffff200008084780>] el0_svc_naked+0x34/0x38
[  728.499957] ==================================================================
[  728.507801] Unable to handle kernel NULL pointer dereference at virtual address 000000a0
[  728.517742] Mem abort info:
[  728.520993]   Exception class = DABT (current EL), IL = 32 bits
[  728.527375]   SET = 0, FnV = 0
[  728.530731]   EA = 0, S1PTW = 0
[  728.534361] Data abort info:
[  728.537650]   ISV = 0, ISS = 0x00000006
[  728.541863]   CM = 0, WnR = 0
[  728.545167] user pgtable: 4k pages, 48-bit VAs, pgd = ffff8006c6100000
[  728.552156] [00000000000000a0] *pgd=0000000716a8d003
[  728.557519] , *pud=00000007116fc003
[  728.561259] , *pmd=0000000000000000
[  728.564985] Internal error: Oops: 96000006 [#1] PREEMPT SMP
[  728.570815] Modules linked in:
[  728.574023]  usb_f_uac2
[  728.576560]  u_audio
[  728.578827]  g_audio(-)
[  728.581361]  libcomposite
[  728.584071]  configfs
[  728.586428]  aes_ce_blk
[  728.588960]  sata_rcar
[  728.591421]  crypto_simd
[  728.594039]  cryptd
[  728.596217]  libata
[  728.598396]  aes_ce_cipher
[  728.601188]  crc32_ce
[  728.603542]  ghash_ce
[  728.605896]  gf128mul
[  728.608250]  aes_arm64
[  728.610692]  scsi_mod
[  728.613046]  sha2_ce
[  728.615313]  xhci_plat_hcd
[  728.618106]  sha256_arm64
[  728.620811]  sha1_ce
[  728.623077]  renesas_usbhs
[  728.625869]  xhci_hcd
[  728.628243]  renesas_usb3
[  728.630948]  sha1_generic
[  728.633670]  ravb_streaming(C)
[  728.636814]  udc_core
[  728.639168]  cpufreq_dt
[  728.641697]  rcar_gen3_thermal
[  728.644840]  usb_dmac
[  728.647194]  pwm_rcar
[  728.649548]  thermal_sys
[  728.652165]  virt_dma
[  728.654519]  mch_core(C)
[  728.657137]  pwm_bl
[  728.659315]  snd_soc_rcar
[  728.662020]  snd_aloop
[  728.664462]  snd_soc_generic_card
[  728.667869]  snd_soc_ak4613
[  728.670749]  ipv6
[  728.672768]  autofs4
[  728.675052] CPU: 0 PID: 2545 Comm: modprobe Tainted: G    B   WC      4.14.47+ #152
[  728.682973] Hardware name: Renesas Salvator-X board based on r8a7795 ES2.0+ (DT)
[  728.690637] task: ffff8006ced38000 task.stack: ffff8006cf6c0000
[  728.696814] PC is at u_audio_stop_capture+0x70/0x268 [u_audio]
[  728.702896] LR is at u_audio_stop_capture+0x70/0x268 [u_audio]
[  728.708964] pc : [<ffff2000021e1618>] lr : [<ffff2000021e1618>] pstate: 60000145
[  728.716620] sp : ffff8006cf6c7a50
[  728.720154] x29: ffff8006cf6c7a50
[  728.723760] x28: ffff8006ced38000
[  728.727272] x27: ffff200008fd7000
[  728.730857] x26: ffff2000021d2340
[  728.734361] x25: 0000000000000000
[  728.737948] x24: ffff200009e94b08
[  728.741452] x23: 00000000000000a0
[  728.745052] x22: 00000000000000a8
[  728.748558] x21: 1ffff000d9ed8f7c
[  728.752142] x20: ffff8006d671a800
[  728.755646] x19: 0000000000000000
[  728.759231] x18: 0000000000000000
[  728.762736] x17: 0000ffffbc7c8f40
[  728.766320] x16: ffff200008213c4c
[  728.769823] x15: 0000000000000000
[  728.773408] x14: 0720072007200720
[  728.776912] x13: 0720072007200720
[  728.780497] x12: ffffffffffffffff
[  728.784001] x11: 0000000000000040
[  728.787598] x10: 0000000000001600
[  728.791103] x9 : ffff8006cf6c77a0
[  728.794689] x8 : ffff8006ced39660
[  728.798193] x7 : ffff20000811c738
[  728.801794] x6 : 0000000000000000
[  728.805299] x5 : dfff200000000000
[  728.808885] x4 : ffff8006ced38000
[  728.812390] x3 : ffff200008fb46e8
[  728.815976] x2 : 0000000000000007
[  728.819480] x1 : 3ba68643e7431500
[  728.823066] x0 : 0000000000000000
[  728.826574] Process modprobe (pid: 2545, stack limit = 0xffff8006cf6c0000)
[  728.833704] Call trace:
[  728.836292] Exception stack(0xffff8006cf6c7910 to 0xffff8006cf6c7a50)
[  728.842987] 7900:                                   0000000000000000 3ba68643e7431500
[  728.851084] 7920: 0000000000000007 ffff200008fb46e8 ffff8006ced38000 dfff200000000000
[  728.859173] 7940: 0000000000000000 ffff20000811c738 ffff8006ced39660 ffff8006cf6c77a0
[  728.867248] 7960: 0000000000001600 0000000000000040 ffffffffffffffff 0720072007200720
[  728.875323] 7980: 0720072007200720 0000000000000000 ffff200008213c4c 0000ffffbc7c8f40
[  728.883412] 79a0: 0000000000000000 0000000000000000 ffff8006d671a800 1ffff000d9ed8f7c
[  728.891485] 79c0: 00000000000000a8 00000000000000a0 ffff200009e94b08 0000000000000000
[  728.899561] 79e0: ffff2000021d2340 ffff200008fd7000 ffff8006ced38000 ffff8006cf6c7a50
[  728.907636] 7a00: ffff2000021e1618 ffff8006cf6c7a50 ffff2000021e1618 0000000060000145
[  728.915710] 7a20: 0000000000000008 0000000000000000 0000ffffffffffff 3ba68643e7431500
[  728.923780] 7a40: ffff8006cf6c7a50 ffff2000021e1618
[  728.928880] [<ffff2000021e1618>] u_audio_stop_capture+0x70/0x268 [u_audio]
[  728.936032] [<ffff2000021f8b7c>] afunc_disable+0x44/0x60 [usb_f_uac2]
[  728.942822] [<ffff20000218177c>] usb_remove_function+0x9c/0x210 [libcomposite]
[  728.950385] [<ffff200002183320>] remove_config.isra.2+0x1d8/0x218 [libcomposite]
[  728.958134] [<ffff200002186c54>] __composite_unbind+0x104/0x1f8 [libcomposite]
[  728.965689] [<ffff200002186d58>] composite_unbind+0x10/0x18 [libcomposite]
[  728.972882] [<ffff20000152f158>] usb_gadget_remove_driver+0xc0/0x170 [udc_core]
[  728.980522] [<ffff20000153154c>] usb_gadget_unregister_driver+0x1cc/0x258 [udc_core]
[  728.988638] [<ffff200002180de8>] usb_composite_unregister+0x10/0x18 [libcomposite]
[  728.996472] [<ffff2000021d035c>] audio_driver_exit+0x14/0x28 [g_audio]
[  729.003231] [<ffff200008213ed4>] SyS_delete_module+0x288/0x32c
[  729.009278] Exception stack(0xffff8006cf6c7ec0 to 0xffff8006cf6c8000)
[  729.015946] 7ec0: 0000000006136428 0000000000000800 0000000000000000 0000ffffd706efe8
[  729.024022] 7ee0: 0000ffffd706efe9 000000000000000a 1999999999999999 0000000000000000
[  729.032099] 7f00: 000000000000006a 000000000042c078 0000000000000000 0000000000000005
[  729.040172] 7f20: 0000000000000000 0000000000000000 0000000000000004 0000000000000000
[  729.048263] 7f40: 000000000042bfc8 0000ffffbc7c8f40 0000000000000000 00000000061363c0
[  729.056337] 7f60: 0000000006136428 0000000000000000 0000000000000000 0000000006136428
[  729.064411] 7f80: 000000000042c000 0000ffffd7071448 000000000042c000 0000000000000000
[  729.072484] 7fa0: 00000000061350c0 0000ffffd7070010 000000000041129c 0000ffffd7070010
[  729.080563] 7fc0: 0000ffffbc7c8f48 0000000060000000 0000000006136428 000000000000006a
[  729.088636] 7fe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[  729.096733] [<ffff200008084780>] el0_svc_naked+0x34/0x38
[  729.102259] Code: 9597d1b3 aa1703e0 9102a276 958792b9 (f9405275)
[  729.108617] ---[ end trace 7560c5fa3d100243 ]---

After this patch is applied, the issue is fixed:
rcar-gen3:/home/root# modprobe g_audio
[   59.217127] g_audio gadget: afunc_bind:565 Error!
[   59.222329] g_audio ee020000.usb: failed to start g_audio: -19
modprobe: ERROR: could not insert 'g_audio': No such device
rcar-gen3:/home/root# modprobe -r g_audio
rcar-gen3:/home/root#

Fixes: f1d3861d ("usb: gadget: f_uac2: fix error handling at afunc_bind")
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>