Re: [PATCH] kasan: migrate copy_user_test to kunit

[Andrey Konovalov]

On Fri, Oct 11, 2024 at 9:16 AM Sabyrzhan Tasbolatov
<snovitoll@xxxxxxxxx> wrote:
>
> Migrate the copy_user_test to the KUnit framework to verify out-of-bound
> detection via KASAN reports in copy_from_user(), copy_to_user() and
> their static functions.
>
> This is the last migrated test in kasan_test_module.c, therefore delete
> the file.
>
> In order to detect OOB access in strncpy_from_user(), we need to move
> kasan_check_write() to the function beginning to cover
> if (can_do_masked_user_access()) {...} branch as well.
>
> Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=212205
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx>
> ---
>  lib/strncpy_from_user.c      |  3 +-
>  mm/kasan/kasan_test_c.c      | 39 +++++++++++++++++
>  mm/kasan/kasan_test_module.c | 81 ------------------------------------
>  3 files changed, 41 insertions(+), 82 deletions(-)
>  delete mode 100644 mm/kasan/kasan_test_module.c
>
> diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
> index 989a12a67872..55c33e4f3c70 100644
> --- a/lib/strncpy_from_user.c
> +++ b/lib/strncpy_from_user.c
> @@ -120,6 +120,8 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
>         if (unlikely(count <= 0))
>                 return 0;
>
> +       kasan_check_write(dst, count);
> +
>         if (can_do_masked_user_access()) {
>                 long retval;
>
> @@ -142,7 +144,6 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
>                 if (max > count)
>                         max = count;
>
> -               kasan_check_write(dst, count);
>                 check_object_size(dst, count, false);

I think we better put both kasan_check_write and check_object_size
into do_strncpy_from_user, as the latter is now (post 2865baf54077)
called from two different places.

Also, please put this change into a separate commit with a Fixes:
2865baf54077 tag.

>                 if (user_read_access_begin(src, max)) {
>                         retval = do_strncpy_from_user(dst, src, count, max);
> diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> index a181e4780d9d..e71a16d0dfb9 100644
> --- a/mm/kasan/kasan_test_c.c
> +++ b/mm/kasan/kasan_test_c.c
> @@ -1954,6 +1954,44 @@ static void rust_uaf(struct kunit *test)
>         KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf());
>  }
>
> +static void copy_user_test_oob(struct kunit *test)
> +{
> +       char *kmem;
> +       char __user *usermem;
> +       unsigned long useraddr;
> +       size_t size = 128 - KASAN_GRANULE_SIZE;
> +       int __maybe_unused unused;
> +
> +       kmem = kunit_kmalloc(test, size, GFP_KERNEL);
> +       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, kmem);
> +
> +       useraddr = kunit_vm_mmap(test, NULL, 0, PAGE_SIZE,
> +                                       PROT_READ | PROT_WRITE | PROT_EXEC,
> +                                       MAP_ANONYMOUS | MAP_PRIVATE, 0);
> +       KUNIT_ASSERT_NE_MSG(test, useraddr, 0,
> +               "Could not create userspace mm");
> +       KUNIT_ASSERT_LT_MSG(test, useraddr, (unsigned long)TASK_SIZE,
> +               "Failed to allocate user memory");
> +
> +       OPTIMIZER_HIDE_VAR(size);
> +       usermem = (char __user *)useraddr;
> +
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               unused = copy_from_user(kmem, usermem, size + 1));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               unused = copy_to_user(usermem, kmem, size + 1));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               unused = __copy_from_user(kmem, usermem, size + 1));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               unused = __copy_to_user(usermem, kmem, size + 1));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               unused = __copy_from_user_inatomic(kmem, usermem, size + 1));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               unused = __copy_to_user_inatomic(usermem, kmem, size + 1));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               unused = strncpy_from_user(kmem, usermem, size + 1));
> +}
> +
>  static struct kunit_case kasan_kunit_test_cases[] = {
>         KUNIT_CASE(kmalloc_oob_right),
>         KUNIT_CASE(kmalloc_oob_left),
> @@ -2028,6 +2066,7 @@ static struct kunit_case kasan_kunit_test_cases[] = {
>         KUNIT_CASE(match_all_ptr_tag),
>         KUNIT_CASE(match_all_mem_tag),
>         KUNIT_CASE(rust_uaf),
> +       KUNIT_CASE(copy_user_test_oob),
>         {}
>  };
>
> diff --git a/mm/kasan/kasan_test_module.c b/mm/kasan/kasan_test_module.c
> deleted file mode 100644
> index 27ec22767e42..000000000000
> --- a/mm/kasan/kasan_test_module.c
> +++ /dev/null
> @@ -1,81 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-only
> -/*
> - *
> - * Copyright (c) 2014 Samsung Electronics Co., Ltd.
> - * Author: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
> - */
> -
> -#define pr_fmt(fmt) "kasan: test: " fmt
> -
> -#include <linux/mman.h>
> -#include <linux/module.h>
> -#include <linux/printk.h>
> -#include <linux/slab.h>
> -#include <linux/uaccess.h>
> -
> -#include "kasan.h"
> -
> -static noinline void __init copy_user_test(void)
> -{
> -       char *kmem;
> -       char __user *usermem;
> -       size_t size = 128 - KASAN_GRANULE_SIZE;
> -       int __maybe_unused unused;
> -
> -       kmem = kmalloc(size, GFP_KERNEL);
> -       if (!kmem)
> -               return;
> -
> -       usermem = (char __user *)vm_mmap(NULL, 0, PAGE_SIZE,
> -                           PROT_READ | PROT_WRITE | PROT_EXEC,
> -                           MAP_ANONYMOUS | MAP_PRIVATE, 0);
> -       if (IS_ERR(usermem)) {
> -               pr_err("Failed to allocate user memory\n");
> -               kfree(kmem);
> -               return;
> -       }
> -
> -       OPTIMIZER_HIDE_VAR(size);
> -
> -       pr_info("out-of-bounds in copy_from_user()\n");
> -       unused = copy_from_user(kmem, usermem, size + 1);
> -
> -       pr_info("out-of-bounds in copy_to_user()\n");
> -       unused = copy_to_user(usermem, kmem, size + 1);
> -
> -       pr_info("out-of-bounds in __copy_from_user()\n");
> -       unused = __copy_from_user(kmem, usermem, size + 1);
> -
> -       pr_info("out-of-bounds in __copy_to_user()\n");
> -       unused = __copy_to_user(usermem, kmem, size + 1);
> -
> -       pr_info("out-of-bounds in __copy_from_user_inatomic()\n");
> -       unused = __copy_from_user_inatomic(kmem, usermem, size + 1);
> -
> -       pr_info("out-of-bounds in __copy_to_user_inatomic()\n");
> -       unused = __copy_to_user_inatomic(usermem, kmem, size + 1);
> -
> -       pr_info("out-of-bounds in strncpy_from_user()\n");
> -       unused = strncpy_from_user(kmem, usermem, size + 1);
> -
> -       vm_munmap((unsigned long)usermem, PAGE_SIZE);
> -       kfree(kmem);
> -}
> -
> -static int __init kasan_test_module_init(void)
> -{
> -       /*
> -        * Temporarily enable multi-shot mode. Otherwise, KASAN would only
> -        * report the first detected bug and panic the kernel if panic_on_warn
> -        * is enabled.
> -        */
> -       bool multishot = kasan_save_enable_multi_shot();
> -
> -       copy_user_test();
> -
> -       kasan_restore_multi_shot(multishot);
> -       return -EAGAIN;
> -}
> -
> -module_init(kasan_test_module_init);
> -MODULE_LICENSE("GPL");

Please also remove the corresponding entries from mm/kasan/Makefile
and lib/Kconfig.kasan and update Documentation/dev-tools/kasan.rst.


> --
> 2.34.1
>