linux-kernel - Re: [PATCH] kernel: sys.c: Avoid copying possible padding bytes in copy_to

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Message-ID: <20191028071856.GA1944@kadam>
Date:   Mon, 28 Oct 2019 10:18:56 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dan Carpenter <error27@...il.com>,
        Julia Lawall <julia.lawall@...6.fr>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] kernel: sys.c: Avoid copying possible padding bytes in
 copy_to_user

On Sat, Oct 26, 2019 at 12:46:08PM -0700, Joe Perches wrote:
> Initialization is not guaranteed to zero padding bytes so
> use an explicit memset instead to avoid leaking any kernel
> content in any possible padding bytes.
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
>  kernel/sys.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sys.c b/kernel/sys.c
> index a611d1..3459a5 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1279,11 +1279,13 @@ SYSCALL_DEFINE1(uname, struct old_utsname __user *, name)
>  
>  SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name)
>  {
> -	struct oldold_utsname tmp = {};
> +	struct oldold_utsname tmp;

oldold_utsname doesn't have an struct holes.  It looks like this:

struct oldold_utsname {
        char sysname[9];
        char nodename[9];
        char release[9];
        char version[9];
        char machine[9];
};

regards,
dan carpenter