linux-kernel - Re: [PATCH] Bluetooth: vhci: Avoid needless snprintf() calls

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Message-ID: <20250415161920.GA1692211@ax162>
Date: Tue, 15 Apr 2025 09:19:20 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: stable@...r.kernel.org, kernel test robot <lkp@...el.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	Luiz Augusto von Dentz <luiz.dentz@...il.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-bluetooth@...r.kernel.org, Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Manish Mandlik <mmandlik@...gle.com>, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: vhci: Avoid needless snprintf() calls

On Tue, Apr 15, 2025 at 09:15:19AM -0700, Kees Cook wrote:
> Avoid double-copying of string literals. Use a "const char *" for each
> string instead of copying from .rodata into stack and then into the skb.
> We can go directly from .rodata to the skb.
> 
> This also works around a Clang bug (that has since been fixed[1]).
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202401250927.1poZERd6-lkp@intel.com/
> Fixes: ab4e4380d4e1 ("Bluetooth: Add vhci devcoredump support")
> Link: https://github.com/llvm/llvm-project/commit/ea2e66aa8b6e363b89df66dc44275a0d7ecd70ce [1]
> Cc: stable@...r.kernel.org
> Signed-off-by: Kees Cook <kees@...nel.org>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
> Cc: Marcel Holtmann <marcel@...tmann.org>
> Cc: Luiz Augusto von Dentz <luiz.dentz@...il.com>
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: linux-bluetooth@...r.kernel.org
> ---
>  drivers/bluetooth/hci_vhci.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_vhci.c b/drivers/bluetooth/hci_vhci.c
> index 7651321d351c..9ac22e4a070b 100644
> --- a/drivers/bluetooth/hci_vhci.c
> +++ b/drivers/bluetooth/hci_vhci.c
> @@ -289,18 +289,18 @@ static void vhci_coredump(struct hci_dev *hdev)
>  
>  static void vhci_coredump_hdr(struct hci_dev *hdev, struct sk_buff *skb)
>  {
> -	char buf[80];
> +	const char *buf;
>  
> -	snprintf(buf, sizeof(buf), "Controller Name: vhci_ctrl\n");
> +	buf = "Controller Name: vhci_ctrl\n";
>  	skb_put_data(skb, buf, strlen(buf));
>  
> -	snprintf(buf, sizeof(buf), "Firmware Version: vhci_fw\n");
> +	buf = "Firmware Version: vhci_fw\n";
>  	skb_put_data(skb, buf, strlen(buf));
>  
> -	snprintf(buf, sizeof(buf), "Driver: vhci_drv\n");
> +	buf = "Driver: vhci_drv\n";
>  	skb_put_data(skb, buf, strlen(buf));
>  
> -	snprintf(buf, sizeof(buf), "Vendor: vhci\n");
> +	buf = "Vendor: vhci\n";
>  	skb_put_data(skb, buf, strlen(buf));
>  }
>  
> -- 
> 2.34.1
>