On Wed, Mar 22, 2017 at 5:06 PM, Andrey Ryabinin
<aryabinin@xxxxxxxxxxxxx> wrote:
> Disable kasan after the first report. There are several reasons for this:
> * Single bug quite often has multiple invalid memory accesses causing
> storm in the dmesg.
> * Write OOB access might corrupt metadata so the next report will print
> bogus alloc/free stacktraces.
> * Reports after the first easily could be not bugs by itself but just side
> effects of the first one.
>
> Given that multiple reports only do harm, it makes sense to disable
> kasan after the first one. Except for the tests in lib/test_kasan.c
> as we obviously want to see all reports from test.
Hi Andrey,
Could you make it configurable via CONFIG_KASAN_SOMETHING (which can
default to showing only the first report)?
I sometimes use KASAN to see what bad accesses a particular bug
causes, and seeing all of them (even knowing that they may be
corrupt/induced) helps a lot.
Thanks!
>
> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> ---
> lib/test_kasan.c | 9 +++++++++
> mm/kasan/report.c | 7 +++++++
> 2 files changed, 16 insertions(+)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 0b1d314..5112663 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -11,6 +11,7 @@
>
> #define pr_fmt(fmt) "kasan test: %s " fmt, __func__
>
> +#include <linux/atomic.h>
> #include <linux/delay.h>
> #include <linux/kernel.h>
> #include <linux/mman.h>
> @@ -21,6 +22,8 @@
> #include <linux/uaccess.h>
> #include <linux/module.h>
>
> +extern atomic_t kasan_report_count;
> +
> /*
> * Note: test functions are marked noinline so that their names appear in
> * reports.
> @@ -474,6 +477,9 @@ static noinline void __init use_after_scope_test(void)
>
> static int __init kmalloc_tests_init(void)
> {
> + /* Rise reports limit high enough to see all the following bugs */
> + atomic_set(&kasan_report_count, 100);
> +
> kmalloc_oob_right();
> kmalloc_oob_left();
> kmalloc_node_oob_right();
> @@ -499,6 +505,9 @@ static int __init kmalloc_tests_init(void)
> ksize_unpoisons_memory();
> copy_user_test();
> use_after_scope_test();
> +
> + /* kasan is unreliable now, disable reports */
> + atomic_set(&kasan_report_count, 0);
> return -EAGAIN;
> }
>
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 718a10a..7eab229 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -13,6 +13,7 @@
> *
> */
>
> +#include <linux/atomic.h>
> #include <linux/ftrace.h>
> #include <linux/kernel.h>
> #include <linux/mm.h>
> @@ -354,6 +355,9 @@ static void kasan_report_error(struct kasan_access_info *info)
> kasan_end_report(&flags);
> }
>
> +atomic_t kasan_report_count = ATOMIC_INIT(1);
> +EXPORT_SYMBOL_GPL(kasan_report_count);
> +
> void kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip)
> {
> @@ -362,6 +366,9 @@ void kasan_report(unsigned long addr, size_t size,
> if (likely(!kasan_report_enabled()))
> return;
>
> + if (atomic_dec_if_positive(&kasan_report_count) < 0)
> + return;
> +
> disable_trace_on_warning();
>
> info.access_addr = (void *)addr;
> --
> 2.10.2
>
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