netdev - [PATCH bpf-next V2 2/4] selftests/bpf: xdp_hw

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Message-ID: <167527271533.937063.5717065138099679142.stgit@firesoul>
Date:   Wed, 01 Feb 2023 18:31:55 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     bpf@...r.kernel.org, Stanislav Fomichev <sdf@...gle.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
        martin.lau@...nel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, dsahern@...il.com,
        willemb@...gle.com, void@...ifault.com, kuba@...nel.org,
        xdp-hints@...-project.net
Subject: [PATCH bpf-next V2 2/4] selftests/bpf: xdp_hw_metadata cleanup cause
 segfault

Using xdp_hw_metadata I experince Segmentation fault
after seeing "detaching bpf program....".

On my system the segfault happened when accessing bpf_obj->skeleton
in xdp_hw_metadata__destroy(bpf_obj) call. That doesn't make any sense
as this memory have not been freed by program at this point in time.

Prior to calling xdp_hw_metadata__destroy(bpf_obj) the function
close_xsk() is called for each RX-queue xsk.  The real bug lays
in close_xsk() that unmap via munmap() the wrong memory pointer.
The call xsk_umem__delete(xsk->umem) will free xsk->umem, thus
the call to munmap(xsk->umem, UMEM_SIZE) will have unpredictable
behavior. And man page explain subsequent references to these
pages will generate SIGSEGV.

Unmapping xsk->umem_area instead removes the segfault.

Fixes: 297a3f124155 ("selftests/bpf: Simple program to dump XDP RX metadata")
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 tools/testing/selftests/bpf/xdp_hw_metadata.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c
index 3823b1c499cc..438083e34cce 100644
--- a/tools/testing/selftests/bpf/xdp_hw_metadata.c
+++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c
@@ -121,7 +121,7 @@ static void close_xsk(struct xsk *xsk)
 		xsk_umem__delete(xsk->umem);
 	if (xsk->socket)
 		xsk_socket__delete(xsk->socket);
-	munmap(xsk->umem, UMEM_SIZE);
+	munmap(xsk->umem_area, UMEM_SIZE);
 }

 static void refill_rx(struct xsk *xsk, __u64 addr)