Re: [PATCH] bpf: fix false positive kmemleak report in bpf_ringbuf_area_alloc()

From: Daniel Borkmann
Date: Mon Jun 28 2021 - 10:22:37 EST

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.

Reported-and-tested-by: syzbot+5d895828587f49e7fe9b@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Rustam Kovhaev <rkovhaev@xxxxxxxxx>

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].)