From 4f62c69f018dba6db5f8d87f1c6bf22f8b3fc397 Mon Sep 17 00:00:00 2001
From: Andrey Konovalov <andreyknvl@google.com>
Date: Fri, 12 Feb 2021 17:14:50 +1100
Subject: [PATCH] FROMGIT: 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@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
(cherry picked from commit 5042e07bc0ff0d680daf5fc2fd3dd3dc51232786
 https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git akpm)
Bug: 172318110
Change-Id: I56f28d8970c3c2cdbeeb8a213ef5fb80ee836710
---
 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 ffebad2f0e6e..1328c468fdb5 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -353,6 +353,25 @@ 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 {
@@ -1050,6 +1069,7 @@ 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 2f33b28e76ad..3972a898db14 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1075,6 +1075,9 @@ 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) {