linux-kernel - Re: [PATCH] vboxsf: fix comparison of signed char constant with unsigned char array elements

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Date:   Wed, 16 Sep 2020 08:14:03 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Colin King <colin.king@...onical.com>,
        Christoph Hellwig <hch@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vboxsf: fix comparison of signed char constant with
 unsigned char array elements

Hi,

On 9/15/20 6:03 PM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The comparison of signed char constants with unsigned char array
> elements leads to checks that are always false. Fix this by declaring
> the VBSF_MOUNT_SIGNATURE_BYTE* macros as octal unsigned int constants
> rather than as signed char constants. (Argueably the U is not necessarily
> required, but add it to be really clear of intent).
> 
> Addresses-Coverity: ("Operands don't affect result")
> Fixes: 0fd169576648 ("fs: Add VirtualBox guest shared folder (vboxsf) support")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

A fix for this has already been queued up:

https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git/log/?h=fixes

Explicit nack for this one, since it will still apply, but combined
with the other fix, it will re-break things.

Regards,

Hans



> ---
>   fs/vboxsf/super.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/vboxsf/super.c b/fs/vboxsf/super.c
> index 25aade344192..986efcb29cc2 100644
> --- a/fs/vboxsf/super.c
> +++ b/fs/vboxsf/super.c
> @@ -21,10 +21,10 @@
>   
>   #define VBOXSF_SUPER_MAGIC 0x786f4256 /* 'VBox' little endian */
>   
> -#define VBSF_MOUNT_SIGNATURE_BYTE_0 ('\000')
> -#define VBSF_MOUNT_SIGNATURE_BYTE_1 ('\377')
> -#define VBSF_MOUNT_SIGNATURE_BYTE_2 ('\376')
> -#define VBSF_MOUNT_SIGNATURE_BYTE_3 ('\375')
> +#define VBSF_MOUNT_SIGNATURE_BYTE_0 0000U
> +#define VBSF_MOUNT_SIGNATURE_BYTE_1 0377U
> +#define VBSF_MOUNT_SIGNATURE_BYTE_2 0376U
> +#define VBSF_MOUNT_SIGNATURE_BYTE_3 0375U
>   
>   static int follow_symlinks;
>   module_param(follow_symlinks, int, 0444);
>