Re: [PATCH 5.15-] efivars: Request at most 512 bytes for variable names

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Mar 17, 2024 at 03:33:21AM +0100, Tim Schumacher wrote:
> commit f45812cc23fb74bef62d4eb8a69fe7218f4b9f2a upstream.
> 
> Work around a quirk in a few old (2011-ish) UEFI implementations, where
> a call to `GetNextVariableName` with a buffer size larger than 512 bytes
> will always return EFI_INVALID_PARAMETER.
> 
> There is some lore around EFI variable names being up to 1024 bytes in
> size, but this has no basis in the UEFI specification, and the upper
> bounds are typically platform specific, and apply to the entire variable
> (name plus payload).
> 
> Given that Linux does not permit creating files with names longer than
> NAME_MAX (255) bytes, 512 bytes (== 256 UTF-16 characters) is a
> reasonable limit.
> 
> Cc: <stable@vger.kernel.org> # 6.1+
> Signed-off-by: Tim Schumacher <timschumi@gmx.de>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> [timschumi@gmx.de: adjusted diff for changed context and code move]
> Signed-off-by: Tim Schumacher <timschumi@gmx.de>
> ---
> Please apply this patch to stable kernel 5.15, 5.10, 5.4, and 4.19
> respectively. Kernel 6.1 and upwards were already handled via CC,
> 5.15 and below required a separate patch due to a slight refactor of
> surrounding code in bbc6d2c6ef22 ("efi: vars: Switch to new wrapper
> layer") and a subsequent code move in 2d82e6227ea1 ("efi: vars: Move
> efivar caching layer into efivarfs").
> 
> Please note that the upper Signed-off-by tags are remnants from the
> original patch, I documented my modifications below them and added
> another sign-off. As far as I was able to gather, this is the expected
> format for diverged stable patches.
> 
> I'm not sure on the specifics of manual stable backports, so let me
> know in case anything doesn't follow the process. The linux-efi team
> and list are on CC both for documentation/review purposes and in case
> a new sign-off/ack of theirs is required.

Now queued up, thanks.

greg k-h