linux-kernel - Re: [PATCH] usercopy: add testcases to check zeroing on failure of usercopy

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Message-ID: <CAGXu5j+ogVnxxu1VuUep6ObAdyJbvxMyN25J+PF+exOJqk2VVg@mail.gmail.com>
Date:   Mon, 13 Feb 2017 10:33:22 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Hoeun Ryu <hoeun.ryu@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] usercopy: add testcases to check zeroing on failure of usercopy

On Sat, Feb 11, 2017 at 10:13 PM, Hoeun Ryu <hoeun.ryu@...il.com> wrote:
> In the hardend usercopy, the destination buffer will be zeroed if
> copy_from_user/get_user fails. This patch adds testcases for it.
> The destination buffer is set with non-zero value before illegal
> copy_from_user/get_user is executed and the buffer is compared to
> zero after usercopy is done.
>
> Signed-off-by: Hoeun Ryu <hoeun.ryu@...il.com>
> ---
>  lib/test_user_copy.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
> index 0ecef3e..54bd898 100644
> --- a/lib/test_user_copy.c
> +++ b/lib/test_user_copy.c
> @@ -41,11 +41,18 @@ static int __init test_user_copy_init(void)
>         char *bad_usermem;
>         unsigned long user_addr;
>         unsigned long value = 0x5A;
> +       char *zerokmem;
>
>         kmem = kmalloc(PAGE_SIZE * 2, GFP_KERNEL);
>         if (!kmem)
>                 return -ENOMEM;
>
> +       zerokmem = kzalloc(PAGE_SIZE * 2, GFP_KERNEL);
> +       if (!zerokmem) {
> +               kfree(kmem);
> +               return -ENOMEM;
> +       }
> +
>         user_addr = vm_mmap(NULL, 0, PAGE_SIZE * 2,
>                             PROT_READ | PROT_WRITE | PROT_EXEC,
>                             MAP_ANONYMOUS | MAP_PRIVATE, 0);
> @@ -69,25 +76,35 @@ static int __init test_user_copy_init(void)
>                     "legitimate put_user failed");
>
>         /* Invalid usage: none of these should succeed. */
> +       memset(kmem, 0x5A, PAGE_SIZE);
>         ret |= test(!copy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
>                                     PAGE_SIZE),
>                     "illegal all-kernel copy_from_user passed");
> +       ret |= test(memcmp(zerokmem, kmem, PAGE_SIZE),
> +                   "zeroing failure for illegal all-kernel copy_from_user");
> +       memset(bad_usermem, 0x5A, PAGE_SIZE);

Oh, actually, ha-ha: this isn't legal: it's a direct copy from kernel
to userspace. :) This needs a copy_to_user()... (and same for the
memcmp...)

>         ret |= test(!copy_from_user(bad_usermem, (char __user *)kmem,
>                                     PAGE_SIZE),
>                     "illegal reversed copy_from_user passed");
> +       ret |= test(memcmp(zerokmem, bad_usermem, PAGE_SIZE),
> +                   "zeroing failure for illegal reversed copy_from_user");
>         ret |= test(!copy_to_user((char __user *)kmem, kmem + PAGE_SIZE,
>                                   PAGE_SIZE),
>                     "illegal all-kernel copy_to_user passed");
>         ret |= test(!copy_to_user((char __user *)kmem, bad_usermem,
>                                   PAGE_SIZE),
>                     "illegal reversed copy_to_user passed");
> +       memset(kmem, 0x5A, PAGE_SIZE);
>         ret |= test(!get_user(value, (unsigned long __user *)kmem),
>                     "illegal get_user passed");
> +       ret |= test(memcmp(zerokmem, kmem, sizeof(value)),
> +                   "zeroing failure for illegal get_user");
>         ret |= test(!put_user(value, (unsigned long __user *)kmem),
>                     "illegal put_user passed");
>
>         vm_munmap(user_addr, PAGE_SIZE * 2);
>         kfree(kmem);
> +       kfree(zerokmem);
>
>         if (ret == 0) {
>                 pr_info("tests passed.\n");
> --
> 2.7.4
>

Can you respin this?

-Kees

-- 
Kees Cook
Pixel Security