linux-kernel - RE: [PATCH] net: ena: replace deprecated strncpy with strscpy

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Message-ID: <fe65f57f91f342c7a173891b84cda37b@amazon.com>
Date:   Thu, 5 Oct 2023 22:25:08 +0000
From:   "Kiyanovski, Arthur" <akiyano@...zon.com>
To:     Justin Stitt <justinstitt@...gle.com>,
        "Agroskin, Shay" <shayagr@...zon.com>,
        "Arinzon, David" <darinzon@...zon.com>,
        "Dagan, Noam" <ndagan@...zon.com>,
        "Bshara, Saeed" <saeedb@...zon.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: RE: [PATCH] net: ena: replace deprecated strncpy with strscpy

> -----Original Message-----
> From: Justin Stitt <justinstitt@...gle.com>
> Sent: Thursday, October 5, 2023 3:56 AM
> To: Agroskin, Shay <shayagr@...zon.com>; Kiyanovski, Arthur
> <akiyano@...zon.com>; Arinzon, David <darinzon@...zon.com>; Dagan,
> Noam <ndagan@...zon.com>; Bshara, Saeed <saeedb@...zon.com>; David
> S. Miller <davem@...emloft.net>; Eric Dumazet <edumazet@...gle.com>;
> Jakub Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> hardening@...r.kernel.org; Justin Stitt <justinstitt@...gle.com>
> Subject: [EXTERNAL] [PATCH] net: ena: replace deprecated strncpy with strscpy
> 
> CAUTION: This email originated from outside of the organization. Do not click
> links or open attachments unless you can confirm the sender and know the
> content is safe.
> 
> 
> 
> `strncpy` is deprecated for use on NUL-terminated destination strings [1] and as
> such we should prefer more robust and less ambiguous string interfaces.
> 
> NUL-padding is not necessary as host_info is initialized to `ena_dev-
> >host_attr.host_info` which is ultimately zero-initialized via
> alloc_etherdev_mq().
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees NUL-
> termination on the destination buffer without unnecessarily NUL-padding.
> 
> Link:
> https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-
> nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
> [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: build-tested only.
> ---
>  drivers/net/ethernet/amazon/ena/ena_netdev.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c
> b/drivers/net/ethernet/amazon/ena/ena_netdev.c
> index f955bde10cf9..3118a617c9b6 100644
> --- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
> +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
> @@ -3276,8 +3276,8 @@ static void ena_config_host_info(struct
> ena_com_dev *ena_dev, struct pci_dev *pd
>         strscpy(host_info->kernel_ver_str, utsname()->version,
>                 sizeof(host_info->kernel_ver_str) - 1);
>         host_info->os_dist = 0;
> -       strncpy(host_info->os_dist_str, utsname()->release,
> -               sizeof(host_info->os_dist_str) - 1);
> +       strscpy(host_info->os_dist_str, utsname()->release,
> +               sizeof(host_info->os_dist_str));
>         host_info->driver_version =
>                 (DRV_MODULE_GEN_MAJOR) |
>                 (DRV_MODULE_GEN_MINOR <<
> ENA_ADMIN_HOST_INFO_MINOR_SHIFT) |
> 
> ---
> base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
> change-id: 20231005-strncpy-drivers-net-ethernet-amazon-ena-ena_netdev-c-
> 6c4804466aa7
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 

Thanks for submitting this change.

The change looks good but the sentence "NUL-padding is not necessary as
host_info is initialized to `ena_dev->host_attr.host_info` which is ultimately
zero-initialized via alloc_etherdev_mq()." is inaccurate. 

host_info allocation is done in ena_com_allocate_host_info() via 
dma_alloc_coherent() and is not zero initialized by alloc_etherdev_mq().

I looked at both the documentation of dma_alloc_coherent() in 
https://www.kernel.org/doc/Documentation/DMA-API.txt
as well as the code itself, and (maybe I'm wrong but) I didn't see 100%
guarantees the that the memory is zero-initialized.

However zero initialization of the destination doesn't matter in this case,
because strscpy() guarantees a NULL termination.

So please just remove this sentence from the commit message.

Thanks,
Arthur Kiyanovski