linux-kernel - Re: [PATCH v2] Bluetooth: coredump: Use tmp buffer with dev

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Message-ID: <d8a85b98-4c70-4fcf-9d7b-bd1de2d780c3@molgen.mpg.de>
Date: Wed, 16 Jul 2025 05:06:38 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Ivan Pravdin <ipravdin.official@...il.com>
Cc: marcel@...tmann.org, johan.hedberg@...il.com, luiz.dentz@...il.com,
 linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzbot+ac3c79181f6aecc5120c@...kaller.appspotmail.com
Subject: Re: [PATCH v2] Bluetooth: coredump: Use tmp buffer with dev_coredumpv

Dear Ivan,


Thank you for your patch and fixing the report.

Am 16.07.25 um 02:37 schrieb Ivan Pravdin:

Personally, I’d start with the problem description.

> Create and use new vmalloc'ed buffer with dev_coredumpv. From
> dev_coredumpv documentation:
> 
> `This function takes ownership of the vmalloc'ed data and will free
> it when it is no longer used.`

You could use email/Markdown style citation by prepending the lines with 
`> `.

> As hdev->dump is used after dev_coredumpv, create temporary buffer to
> hold hdev->dump data.
> 
> Reported-by: syzbot+ac3c79181f6aecc5120c@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/67eaa688.050a0220.1547ec.014a.GAE@google.com

Add a trace excerpt to the commit message?

> Fixes: b257e02ecc46 ("HCI: coredump: Log devcd dumps into the monitor")
> Signed-off-by: Ivan Pravdin <ipravdin.official@...il.com>
> ---
> v1 -> v2: Changed subject prefix to Bluetooth:
> 
>   net/bluetooth/coredump.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bluetooth/coredump.c b/net/bluetooth/coredump.c
> index 819eacb38762..1232c9a94f95 100644
> --- a/net/bluetooth/coredump.c
> +++ b/net/bluetooth/coredump.c
> @@ -243,6 +243,7 @@ static void hci_devcd_handle_pkt_pattern(struct hci_dev *hdev,
>   static void hci_devcd_dump(struct hci_dev *hdev)
>   {
>   	struct sk_buff *skb;
> +	char *coredump;
>   	u32 size;
>   
>   	bt_dev_dbg(hdev, "state %d", hdev->dump.state);
> @@ -250,7 +251,11 @@ static void hci_devcd_dump(struct hci_dev *hdev)
>   	size = hdev->dump.tail - hdev->dump.head;
>   
>   	/* Emit a devcoredump with the available data */
> -	dev_coredumpv(&hdev->dev, hdev->dump.head, size, GFP_KERNEL);
> +	coredump = vmalloc(size);
> +	if (coredump) {
> +		memcpy(coredump, hdev->dump.head, size);
> +		dev_coredumpv(&hdev->dev, coredump, size, GFP_KERNEL);
> +	}

Should it be logged, if allocation fails?

>   
>   	/* Send a copy to monitor as a diagnostic packet */
>   	skb = bt_skb_alloc(size, GFP_ATOMIC);


Kind regards,

Paul