[PATCH] kasan: separate double free case from invalid free

[Kuan-Ying Lee]

Currently, KASAN describes all invalid-free/double-free bugs as
"double-free or invalid-free". This is ambiguous.

KASAN should report "double-free" when a double-free is a more
likely cause (the address points to the start of an object) and
report "invalid-free" otherwise [1].

[1] https://bugzilla.kernel.org/show_bug.cgi?id=212193

Signed-off-by: Kuan-Ying Lee <Kuan-Y...@mediatek.com>
---
mm/kasan/common.c | 8 ++++----
mm/kasan/kasan.h | 3 ++-
mm/kasan/report.c | 12 ++++++++----
3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index c40c0e7b3b5f..707c3a527fcb 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -343,7 +343,7 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,

if (unlikely(nearest_obj(cache, virt_to_slab(object), object) !=
object)) {
- kasan_report_invalid_free(tagged_object, ip);
+ kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_INVALID_FREE);
return true;
}

@@ -352,7 +352,7 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
return false;

if (!kasan_byte_accessible(tagged_object)) {
- kasan_report_invalid_free(tagged_object, ip);
+ kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_DOUBLE_FREE);
return true;
}

@@ -377,12 +377,12 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object,
static inline bool ____kasan_kfree_large(void *ptr, unsigned long ip)
{
if (ptr != page_address(virt_to_head_page(ptr))) {
- kasan_report_invalid_free(ptr, ip);
+ kasan_report_invalid_free(ptr, ip, KASAN_REPORT_INVALID_FREE);
return true;
}

if (!kasan_byte_accessible(ptr)) {
- kasan_report_invalid_free(ptr, ip);
+ kasan_report_invalid_free(ptr, ip, KASAN_REPORT_DOUBLE_FREE);
return true;
}

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 610d60d6e5b8..01c03e45acd4 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -125,6 +125,7 @@ static inline bool kasan_sync_fault_possible(void)
enum kasan_report_type {
KASAN_REPORT_ACCESS,
KASAN_REPORT_INVALID_FREE,
+ KASAN_REPORT_DOUBLE_FREE,
};

struct kasan_report_info {
@@ -277,7 +278,7 @@ static inline void kasan_print_address_stack_frame(const void *addr) { }

bool kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
-void kasan_report_invalid_free(void *object, unsigned long ip);
+void kasan_report_invalid_free(void *object, unsigned long ip, enum kasan_report_type type);

struct page *kasan_addr_to_page(const void *addr);
struct slab *kasan_addr_to_slab(const void *addr);
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index b341a191651d..fe3f606b3a98 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -176,8 +176,12 @@ static void end_report(unsigned long *flags, void *addr)
static void print_error_description(struct kasan_report_info *info)
{
if (info->type == KASAN_REPORT_INVALID_FREE) {
- pr_err("BUG: KASAN: double-free or invalid-free in %pS\n",
- (void *)info->ip);
+ pr_err("BUG: KASAN: invalid-free in %pS\n", (void *)info->ip);
+ return;
+ }
+
+ if (info->type == KASAN_REPORT_DOUBLE_FREE) {
+ pr_err("BUG: KASAN: double-free in %pS\n", (void *)info->ip);
return;
}

@@ -433,7 +437,7 @@ static void print_report(struct kasan_report_info *info)
}
}

-void kasan_report_invalid_free(void *ptr, unsigned long ip)
+void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_type type)
{
unsigned long flags;
struct kasan_report_info info;
@@ -448,7 +452,7 @@ void kasan_report_invalid_free(void *ptr, unsigned long ip)

start_report(&flags, true);

- info.type = KASAN_REPORT_INVALID_FREE;
+ info.type = type;
info.access_addr = ptr;
info.first_bad_addr = kasan_reset_tag(ptr);
info.access_size = 0;
--
2.18.0

[Andrew Morton]

On Wed, 15 Jun 2022 14:22:18 +0800 Kuan-Ying Lee <Kuan-Y...@mediatek.com> wrote:

> Currently, KASAN describes all invalid-free/double-free bugs as
> "double-free or invalid-free". This is ambiguous.
>
> KASAN should report "double-free" when a double-free is a more
> likely cause (the address points to the start of an object) and
> report "invalid-free" otherwise [1].
>
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=212193
>

> ...

Could we please have some review of this?

Thanks.

[Dmitry Vyukov]

On Mon, 4 Jul 2022 at 01:15, Andrew Morton <ak...@linux-foundation.org> wrote:
>
> On Wed, 15 Jun 2022 14:22:18 +0800 Kuan-Ying Lee <Kuan-Y...@mediatek.com> wrote:
>
> > Currently, KASAN describes all invalid-free/double-free bugs as
> > "double-free or invalid-free". This is ambiguous.
> >
> > KASAN should report "double-free" when a double-free is a more
> > likely cause (the address points to the start of an object) and
> > report "invalid-free" otherwise [1].
> >
> > [1] https://bugzilla.kernel.org/show_bug.cgi?id=212193
> >
> > ...
>
> Could we please have some review of this?

Looks reasonable to me.
Looking through git log it seems the only reason to combine them was
laziness/didn't seem important enough.

Reviewed-by: Dmitry Vyukov <dvy...@google.com>

I will update syzkaller parsing of bug messages to not produce
duplicates for existing double-frees.
Not sure if anything needs to be done for other kernel testing systems.

[Andrey Konovalov]

Reviewed-by: Andrey Konovalov <andre...@gmail.com>

Thanks for the patch!