* [PATCH] bpf: fix false positive kmemleak report in bpf_ringbuf_area_alloc()
@ 2021-06-26 18:11 Rustam Kovhaev
2021-06-28 14:19 ` Daniel Borkmann
0 siblings, 1 reply; 2+ messages in thread
From: Rustam Kovhaev @ 2021-06-26 18:11 UTC (permalink / raw)
To: ast, andrii, daniel, kafai, songliubraving, yhs, john.fastabend, kpsingh
Cc: netdev, bpf, linux-kernel, Rustam Kovhaev
kmemleak scans struct page, but it does not scan the page content.
if we allocate some memory with kmalloc(), then allocate page with
alloc_page(), and if we put kmalloc pointer somewhere inside that page,
kmemleak will report kmalloc pointer as a false positive.
we can instruct kmemleak to scan the memory area by calling
kmemleak_alloc()/kmemleak_free(), but part of struct bpf_ringbuf is
mmaped to user space, and if struct bpf_ringbuf changes we would have to
revisit and review size argument in kmemleak_alloc(), because we do not
want kmemleak to scan the user space memory.
let's simplify things and use kmemleak_not_leak() here.
Link: https://lore.kernel.org/lkml/YNTAqiE7CWJhOK2M@nuc10/
Link: https://lore.kernel.org/lkml/20210615101515.GC26027@arm.com/
Link: https://syzkaller.appspot.com/bug?extid=5d895828587f49e7fe9b
Reported-and-tested-by: syzbot+5d895828587f49e7fe9b@syzkaller.appspotmail.com
Signed-off-by: Rustam Kovhaev <rkovhaev@gmail.com>
---
kernel/bpf/ringbuf.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index 84b3b35fc0d0..9e0c10c6892a 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -8,6 +8,7 @@
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/poll.h>
+#include <linux/kmemleak.h>
#include <uapi/linux/btf.h>
#define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE)
@@ -105,6 +106,7 @@ static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node)
rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages,
VM_ALLOC | VM_USERMAP, PAGE_KERNEL);
if (rb) {
+ kmemleak_not_leak(pages);
rb->pages = pages;
rb->nr_pages = nr_pages;
return rb;
--
2.30.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] bpf: fix false positive kmemleak report in bpf_ringbuf_area_alloc()
2021-06-26 18:11 [PATCH] bpf: fix false positive kmemleak report in bpf_ringbuf_area_alloc() Rustam Kovhaev
@ 2021-06-28 14:19 ` Daniel Borkmann
0 siblings, 0 replies; 2+ messages in thread
From: Daniel Borkmann @ 2021-06-28 14:19 UTC (permalink / raw)
To: Rustam Kovhaev, ast, andrii, kafai, songliubraving, yhs,
john.fastabend, kpsingh
Cc: netdev, bpf, linux-kernel, dvyukov, andrii
On 6/26/21 8:11 PM, Rustam Kovhaev wrote:
> kmemleak scans struct page, but it does not scan the page content.
> if we allocate some memory with kmalloc(), then allocate page with
> alloc_page(), and if we put kmalloc pointer somewhere inside that page,
> kmemleak will report kmalloc pointer as a false positive.
>
> we can instruct kmemleak to scan the memory area by calling
> kmemleak_alloc()/kmemleak_free(), but part of struct bpf_ringbuf is
> mmaped to user space, and if struct bpf_ringbuf changes we would have to
> revisit and review size argument in kmemleak_alloc(), because we do not
> want kmemleak to scan the user space memory.
> let's simplify things and use kmemleak_not_leak() here.
>
> Link: https://lore.kernel.org/lkml/YNTAqiE7CWJhOK2M@nuc10/
> Link: https://lore.kernel.org/lkml/20210615101515.GC26027@arm.com/
> Link: https://syzkaller.appspot.com/bug?extid=5d895828587f49e7fe9b
> Reported-and-tested-by: syzbot+5d895828587f49e7fe9b@syzkaller.appspotmail.com
> Signed-off-by: Rustam Kovhaev <rkovhaev@gmail.com>
Applied, thanks! (Also included Andrii's prior analysis as well to the commit
log so there's a bit more context if we need to revisit in future [0].)
[0] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=ccff81e1d028bbbf8573d3364a87542386c707bf
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