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authorMarco Elver <elver@google.com>2019-07-11 20:54:18 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-07-12 11:05:42 -0700
commit0d4ca4c9bab397b525c9a4f875d31410ce4bc738 (patch)
tree7b7cc749aaa40c923e14870def61b57d56564732
parent10d1f8cb3965a6f633bf23eb984cda552927e3a5 (diff)
mm/kasan: add object validation in ksize()
ksize() has been unconditionally unpoisoning the whole shadow memory region associated with an allocation. This can lead to various undetected bugs, for example, double-kzfree(). Specifically, kzfree() uses ksize() to determine the actual allocation size, and subsequently zeroes the memory. Since ksize() used to just unpoison the whole shadow memory region, no invalid free was detected. This patch addresses this as follows: 1. Add a check in ksize(), and only then unpoison the memory region. 2. Preserve kasan_unpoison_slab() semantics by explicitly unpoisoning the shadow memory region using the size obtained from __ksize(). Tested: 1. With SLAB allocator: a) normal boot without warnings; b) verified the added double-kzfree() is detected. 2. With SLUB allocator: a) normal boot without warnings; b) verified the added double-kzfree() is detected. [elver@google.com: s/BUG_ON/WARN_ON_ONCE/, per Kees] Link: http://lkml.kernel.org/r/20190627094445.216365-6-elver@google.com Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199359 Link: http://lkml.kernel.org/r/20190626142014.141844-6-elver@google.com Signed-off-by: Marco Elver <elver@google.com> Acked-by: Kees Cook <keescook@chromium.org> Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Konovalov <andreyknvl@google.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/kasan.h7
-rw-r--r--mm/slab_common.c22
2 files changed, 26 insertions, 3 deletions
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b40ea104dd36..cc8a03cc9674 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -76,8 +76,11 @@ void kasan_free_shadow(const struct vm_struct *vm);
int kasan_add_zero_shadow(void *start, unsigned long size);
void kasan_remove_zero_shadow(void *start, unsigned long size);
-size_t ksize(const void *);
-static inline void kasan_unpoison_slab(const void *ptr) { ksize(ptr); }
+size_t __ksize(const void *);
+static inline void kasan_unpoison_slab(const void *ptr)
+{
+ kasan_unpoison_shadow(ptr, __ksize(ptr));
+}
size_t kasan_metadata_size(struct kmem_cache *cache);
bool kasan_save_enable_multi_shot(void);
diff --git a/mm/slab_common.c b/mm/slab_common.c
index b7c6a40e436a..a09bb10aa026 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1613,7 +1613,27 @@ EXPORT_SYMBOL(kzfree);
*/
size_t ksize(const void *objp)
{
- size_t size = __ksize(objp);
+ size_t size;
+
+ if (WARN_ON_ONCE(!objp))
+ return 0;
+ /*
+ * We need to check that the pointed to object is valid, and only then
+ * unpoison the shadow memory below. We use __kasan_check_read(), to
+ * generate a more useful report at the time ksize() is called (rather
+ * than later where behaviour is undefined due to potential
+ * use-after-free or double-free).
+ *
+ * If the pointed to memory is invalid we return 0, to avoid users of
+ * ksize() writing to and potentially corrupting the memory region.
+ *
+ * We want to perform the check before __ksize(), to avoid potentially
+ * crashing in __ksize() due to accessing invalid metadata.
+ */
+ if (unlikely(objp == ZERO_SIZE_PTR) || !__kasan_check_read(objp, 1))
+ return 0;
+
+ size = __ksize(objp);
/*
* We assume that ksize callers could use whole allocated area,
* so we need to unpoison this area.