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/ (local)
Link: https://lore.kernel.org/lkml/20210615101515.GC26027@arm.com/ (local)
Link: https://syzkaller.appspot.com/bug?extid=5d895828587f49e7fe9b
Reported-and-tested-by: syzbot+5d895828587f49e7fe9b@syzkaller.appspotmail.com
Signed-off-by: Rustam Kovhaev <redacted>

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