[PATCH v2 07/12] kasan, mm: fail krealloc on freed objects
From: Andrey Konovalov <hidden>
Date: 2021-02-05 23:47:01
Also in:
linux-mm, lkml
Subsystem:
library code, memory management, slab allocator, the rest · Maintainers:
Andrew Morton, Vlastimil Babka, Harry Yoo, Linus Torvalds
Currently, if krealloc() is called on a freed object with KASAN enabled, it allocates and returns a new object, but doesn't copy any memory from the old one as ksize() returns 0. This makes the caller believe that krealloc() succeeded (KASAN report is printed though). This patch adds an accessibility check into __do_krealloc(). If the check fails, krealloc() returns NULL. This check duplicates the one in ksize(); this is fixed in the following patch. This patch also adds a KASAN-KUnit test to check krealloc() behaviour when it's called on a freed object. Reviewed-by: Marco Elver <elver@google.com> Signed-off-by: Andrey Konovalov <redacted> --- lib/test_kasan.c | 20 ++++++++++++++++++++ mm/slab_common.c | 3 +++ 2 files changed, 23 insertions(+)
diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 6e63ba62db09..791164ef191b 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c@@ -359,6 +359,25 @@ static void krealloc_pagealloc_less_oob(struct kunit *test) KMALLOC_MAX_CACHE_SIZE + 201); } +/* + * Check that krealloc() detects a use-after-free, returns NULL, + * and doesn't unpoison the freed object. + */ +static void krealloc_uaf(struct kunit *test) +{ + char *ptr1, *ptr2; + int size1 = 201; + int size2 = 235; + + ptr1 = kmalloc(size1, GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1); + kfree(ptr1); + + KUNIT_EXPECT_KASAN_FAIL(test, ptr2 = krealloc(ptr1, size2, GFP_KERNEL)); + KUNIT_ASSERT_PTR_EQ(test, (void *)ptr2, NULL); + KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)ptr1); +} + static void kmalloc_oob_16(struct kunit *test) { struct {
@@ -1056,6 +1075,7 @@ static struct kunit_case kasan_kunit_test_cases[] = { KUNIT_CASE(krealloc_less_oob), KUNIT_CASE(krealloc_pagealloc_more_oob), KUNIT_CASE(krealloc_pagealloc_less_oob), + KUNIT_CASE(krealloc_uaf), KUNIT_CASE(kmalloc_oob_16), KUNIT_CASE(kmalloc_uaf_16), KUNIT_CASE(kmalloc_oob_in_memset),
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 39d1a8ff9bb8..dad70239b54c 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c@@ -1140,6 +1140,9 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size, void *ret; size_t ks; + if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p)) + return NULL; + ks = ksize(p); if (ks >= new_size) {
--
2.30.0.365.g02bc693789-goog
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