linux-kernel - Re: [PATCH v2] kasan: fix kmemleak false-positive in kasan_module

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Date:	Wed, 18 Nov 2015 10:20:49 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kasan: fix kmemleak false-positive in kasan_module_alloc()

On 18 November 2015 at 09:26, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
> Kmemleak reports the following leak:
>         unreferenced object 0xfffffbfff41ea000 (size 20480):
>         comm "modprobe", pid 65199, jiffies 4298875551 (age 542.568s)
>         hex dump (first 32 bytes):
>           00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>           00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>         backtrace:
>           [<ffffffff82354f5e>] kmemleak_alloc+0x4e/0xc0
>           [<ffffffff8152e718>] __vmalloc_node_range+0x4b8/0x740
>           [<ffffffff81574072>] kasan_module_alloc+0x72/0xc0
>           [<ffffffff810efe68>] module_alloc+0x78/0xb0
>           [<ffffffff812f6a24>] module_alloc_update_bounds+0x14/0x70
>           [<ffffffff812f8184>] layout_and_allocate+0x16f4/0x3c90
>           [<ffffffff812faa1f>] load_module+0x2ff/0x6690
>           [<ffffffff813010b6>] SyS_finit_module+0x136/0x170
>           [<ffffffff8239bbc9>] system_call_fastpath+0x16/0x1b
>           [<ffffffffffffffff>] 0xffffffffffffffff
>
> kasan_module_alloc() allocates shadow memory for module and frees it on
> module unloading. It doesn't store the pointer to allocated shadow memory
> because it could be calculated from the shadowed address, i.e. kasan_mem_to_shadow(addr).
> Since kmemleak cannot find pointer to allocated shadow, it thinks that
> memory leaked.
>
> Use kmemleak_ignore() to tell kmemleak that this is not a leak and shadow
> memory doesn't contain any pointers.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Catalin Marinas <catalin.marinas@....com>

Acked-by: Catalin Marinas <catalin.marinas@....com>
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