From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan, mm: fail krealloc on freed objects 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. Link: https://lkml.kernel.org/r/cbcf7b02be0a1ca11de4f833f2ff0b3f2c9b00c8.1612546384.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Branislav Rankov <Branislav.Rankov@xxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx> Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx> Cc: Peter Collingbourne <pcc@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/test_kasan.c | 20 ++++++++++++++++++++ mm/slab_common.c | 3 +++ 2 files changed, 23 insertions(+) --- a/lib/test_kasan.c~kasan-mm-fail-krealloc-on-freed-objects +++ a/lib/test_kasan.c @@ -353,6 +353,25 @@ static void krealloc_pagealloc_less_oob( 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 { @@ -1050,6 +1069,7 @@ static struct kunit_case kasan_kunit_tes 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), --- a/mm/slab_common.c~kasan-mm-fail-krealloc-on-freed-objects +++ a/mm/slab_common.c @@ -1136,6 +1136,9 @@ static __always_inline void *__do_kreall 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) { _
