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Date:   Fri, 22 Mar 2019 06:36:02 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     fei.yang@...el.com
Cc:     balbi@...nel.org, andrzej.p@...labora.com, plr.vincent@...il.com,
        jingx.shen@...el.com, john.stultz@...aro.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] usb: gadget: f_fs: don't free buffer prematurely

On Thu, Mar 21, 2019 at 02:31:14PM -0700, fei.yang@...el.com wrote:
> From: Fei Yang <fei.yang@...el.com>
> 
> The following kernel panic happens due to the io_data buffer gets deallocated
> before the async io is completed. Add a check for the case where io_data buffer
> should be deallocated by ffs_user_copy_worker.
> 
> [   41.663334] BUG: unable to handle kernel NULL pointer dereference at 0000000000000048
> [   41.672099] #PF error: [normal kernel read fault]
> [   41.677356] PGD 20c974067 P4D 20c974067 PUD 20c973067 PMD 0
> [   41.683687] Oops: 0000 [#1] PREEMPT SMP
> [   41.687976] CPU: 1 PID: 7 Comm: kworker/u8:0 Tainted: G     U            5.0.0-quilt-2e5dc0ac-00790-gd8c79f2-dirty #2
> [   41.705309] Workqueue: adb ffs_user_copy_worker
> [   41.705316] RIP: 0010:__vunmap+0x2a/0xc0
> [   41.705318] Code: 0f 1f 44 00 00 48 85 ff 0f 84 87 00 00 00 55 f7 c7 ff 0f 00 00 48 89 e5 41 55 41 89 f5 41 54 53 48 89 fb 75 71 e8 56 d7 ff ff <4c> 8b 60 48 4d 85 e4 74 76 48 89 df e8 25 ff ff ff 45 85 ed 74 46
> [   41.705320] RSP: 0018:ffffbc3a40053df0 EFLAGS: 00010286
> [   41.705322] RAX: 0000000000000000 RBX: ffffbc3a406f1000 RCX: 0000000000000000
> [   41.705323] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 00000000ffffffff
> [   41.705324] RBP: ffffbc3a40053e08 R08: 000000000001fb79 R09: 0000000000000037
> [   41.705325] R10: ffffbc3a40053b68 R11: ffffbc3a40053cad R12: fffffffffffffff2
> [   41.705326] R13: 0000000000000001 R14: 0000000000000000 R15: ffffffffffffffff
> [   41.705328] FS:  0000000000000000(0000) GS:ffff9e2977a80000(0000) knlGS:0000000000000000
> [   41.705329] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   41.705330] CR2: 0000000000000048 CR3: 000000020c994000 CR4: 00000000003406e0
> [   41.705331] Call Trace:
> [   41.705338]  vfree+0x50/0xb0
> [   41.705341]  ffs_user_copy_worker+0xe9/0x1c0
> [   41.705344]  process_one_work+0x19f/0x3e0
> [   41.705348]  worker_thread+0x3f/0x3b0
> [   41.829766]  kthread+0x12b/0x150
> [   41.833371]  ? process_one_work+0x3e0/0x3e0
> [   41.838045]  ? kthread_create_worker_on_cpu+0x70/0x70
> [   41.843695]  ret_from_fork+0x3a/0x50
> [   41.847689] Modules linked in: hci_uart bluetooth ecdh_generic rfkill_gpio dwc3_pci dwc3 snd_usb_audio mei_me tpm_crb snd_usbmidi_lib xhci_pci xhci_hcd mei tpm snd_hwdep cfg80211 snd_soc_skl snd_soc_skl_ipc snd_soc_sst_ipc snd_soc_sst_dsp snd_hda_ext_core snd_hda_core videobuf2_dma_sg crlmodule
> [   41.876880] CR2: 0000000000000048
> [   41.880584] ---[ end trace 2bc4addff0f2e673 ]---
> [   41.891346] RIP: 0010:__vunmap+0x2a/0xc0
> [   41.895734] Code: 0f 1f 44 00 00 48 85 ff 0f 84 87 00 00 00 55 f7 c7 ff 0f 00 00 48 89 e5 41 55 41 89 f5 41 54 53 48 89 fb 75 71 e8 56 d7 ff ff <4c> 8b 60 48 4d 85 e4 74 76 48 89 df e8 25 ff ff ff 45 85 ed 74 46
> [   41.916740] RSP: 0018:ffffbc3a40053df0 EFLAGS: 00010286
> [   41.922583] RAX: 0000000000000000 RBX: ffffbc3a406f1000 RCX: 0000000000000000
> [   41.930563] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 00000000ffffffff
> [   41.938540] RBP: ffffbc3a40053e08 R08: 000000000001fb79 R09: 0000000000000037
> [   41.946520] R10: ffffbc3a40053b68 R11: ffffbc3a40053cad R12: fffffffffffffff2
> [   41.954502] R13: 0000000000000001 R14: 0000000000000000 R15: ffffffffffffffff
> [   41.962482] FS:  0000000000000000(0000) GS:ffff9e2977a80000(0000) knlGS:0000000000000000
> [   41.971536] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   41.977960] CR2: 0000000000000048 CR3: 000000020c994000 CR4: 00000000003406e0
> [   41.985930] Kernel panic - not syncing: Fatal exception
> [   41.991817] Kernel Offset: 0x16000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
> [   42.009525] Rebooting in 10 seconds..
> [   52.014376] ACPI MEMORY or I/O RESET_REG.
> 
> Fixes: 772a7a724f6 ("usb: gadget: f_fs: Allow scatter-gather buffers")
> Signed-off-by: Fei Yang <fei.yang@...el.com>
> Reviewed-by: Manu Gautam <mgautam@...eaurora.org>
> Tested-by: John Stultz <john.stultz@...aro.org>
> ---
> v2: add tag: "Fixes: 772a7a724f6 ......", Reviewed-by and Tested-by.
> v3: check data for NULL instead of "ret == -EIOCBQUEUED", which would be safer
>     and keep the original logic intact.

If it "fixes" a problem in 5.0, we should add a:
	Cc: stable <stable@...r.kernel.org>
to it as well.

thanks,

greg k-h

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