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![Kees Cook](/assets/img/avatar_default.png)
Replacing compile-time safe calls of strcpy()-related functions with strscpy() was always calling the full strscpy() logic when a builtin would be better. For example: char buf[16]; strcpy(buf, "yes"); would reduce to __builtin_memcpy(buf, "yes", 4), but not if it was: strscpy(buf, yes, sizeof(buf)); Fix this by checking if all sizes are known at compile-time. Cc: linux-hardening@vger.kernel.org Tested-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org>
142 lines
4.5 KiB
C
142 lines
4.5 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* Kernel module for testing 'strscpy' family of functions.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <kunit/test.h>
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#include <linux/string.h>
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/*
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* tc() - Run a specific test case.
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* @src: Source string, argument to strscpy_pad()
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* @count: Size of destination buffer, argument to strscpy_pad()
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* @expected: Expected return value from call to strscpy_pad()
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* @terminator: 1 if there should be a terminating null byte 0 otherwise.
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* @chars: Number of characters from the src string expected to be
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* written to the dst buffer.
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* @pad: Number of pad characters expected (in the tail of dst buffer).
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* (@pad does not include the null terminator byte.)
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*
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* Calls strscpy_pad() and verifies the return value and state of the
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* destination buffer after the call returns.
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*/
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static void tc(struct kunit *test, char *src, int count, int expected,
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int chars, int terminator, int pad)
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{
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int nr_bytes_poison;
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int max_expected;
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int max_count;
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int written;
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char buf[6];
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int index, i;
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const char POISON = 'z';
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KUNIT_ASSERT_TRUE_MSG(test, src != NULL,
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"null source string not supported");
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memset(buf, POISON, sizeof(buf));
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/* Future proofing test suite, validate args */
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max_count = sizeof(buf) - 2; /* Space for null and to verify overflow */
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max_expected = count - 1; /* Space for the null */
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KUNIT_ASSERT_LE_MSG(test, count, max_count,
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"count (%d) is too big (%d) ... aborting", count, max_count);
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KUNIT_EXPECT_LE_MSG(test, expected, max_expected,
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"expected (%d) is bigger than can possibly be returned (%d)",
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expected, max_expected);
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written = strscpy_pad(buf, src, count);
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KUNIT_ASSERT_EQ(test, written, expected);
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if (count && written == -E2BIG) {
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KUNIT_ASSERT_EQ_MSG(test, 0, strncmp(buf, src, count - 1),
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"buffer state invalid for -E2BIG");
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KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
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"too big string is not null terminated correctly");
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}
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for (i = 0; i < chars; i++)
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KUNIT_ASSERT_EQ_MSG(test, buf[i], src[i],
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"buf[i]==%c != src[i]==%c", buf[i], src[i]);
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if (terminator)
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KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
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"string is not null terminated correctly");
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for (i = 0; i < pad; i++) {
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index = chars + terminator + i;
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KUNIT_ASSERT_EQ_MSG(test, buf[index], '\0',
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"padding missing at index: %d", i);
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}
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nr_bytes_poison = sizeof(buf) - chars - terminator - pad;
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for (i = 0; i < nr_bytes_poison; i++) {
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index = sizeof(buf) - 1 - i; /* Check from the end back */
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KUNIT_ASSERT_EQ_MSG(test, buf[index], POISON,
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"poison value missing at index: %d", i);
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}
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}
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static void strscpy_test(struct kunit *test)
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{
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char dest[8];
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/*
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* tc() uses a destination buffer of size 6 and needs at
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* least 2 characters spare (one for null and one to check for
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* overflow). This means we should only call tc() with
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* strings up to a maximum of 4 characters long and 'count'
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* should not exceed 4. To test with longer strings increase
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* the buffer size in tc().
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*/
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/* tc(test, src, count, expected, chars, terminator, pad) */
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tc(test, "a", 0, -E2BIG, 0, 0, 0);
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tc(test, "", 0, -E2BIG, 0, 0, 0);
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tc(test, "a", 1, -E2BIG, 0, 1, 0);
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tc(test, "", 1, 0, 0, 1, 0);
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tc(test, "ab", 2, -E2BIG, 1, 1, 0);
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tc(test, "a", 2, 1, 1, 1, 0);
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tc(test, "", 2, 0, 0, 1, 1);
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tc(test, "abc", 3, -E2BIG, 2, 1, 0);
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tc(test, "ab", 3, 2, 2, 1, 0);
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tc(test, "a", 3, 1, 1, 1, 1);
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tc(test, "", 3, 0, 0, 1, 2);
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tc(test, "abcd", 4, -E2BIG, 3, 1, 0);
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tc(test, "abc", 4, 3, 3, 1, 0);
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tc(test, "ab", 4, 2, 2, 1, 1);
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tc(test, "a", 4, 1, 1, 1, 2);
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tc(test, "", 4, 0, 0, 1, 3);
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/* Compile-time-known source strings. */
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KUNIT_EXPECT_EQ(test, strscpy(dest, "", ARRAY_SIZE(dest)), 0);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "", 3), 0);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "", 1), 0);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "", 0), -E2BIG);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", ARRAY_SIZE(dest)), 5);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 3), -E2BIG);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 1), -E2BIG);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 0), -E2BIG);
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KUNIT_EXPECT_EQ(test, strscpy(dest, "This is too long", ARRAY_SIZE(dest)), -E2BIG);
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}
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static struct kunit_case strscpy_test_cases[] = {
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KUNIT_CASE(strscpy_test),
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{}
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};
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static struct kunit_suite strscpy_test_suite = {
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.name = "strscpy",
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.test_cases = strscpy_test_cases,
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};
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kunit_test_suite(strscpy_test_suite);
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MODULE_AUTHOR("Tobin C. Harding <tobin@kernel.org>");
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MODULE_LICENSE("GPL");
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