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The bpf infrastructure and verifier goes to great length to avoid
bpf progs leaking kernel (pointer) info.
For queueing an xdp_buff via XDP_REDIRECT, xdp_frame info stores
kernel info (incl pointers) in top part of frame data (xdp->data_hard_start).
Checks are in place to assure enough headroom is available for this.
This info is not cleared, and if the frame is reused, then a
malicious user could use bpf_xdp_adjust_head helper to move
xdp->data into this area. Thus, making this area readable.
This is not super critical as XDP progs requires root or
CAP_SYS_ADMIN, which are privileged enough for such info. An
effort (is underway) towards moving networking bpf hooks to the
lesser privileged mode CAP_NET_ADMIN, where leaking such info
should be avoided. Thus, this patch to clear the info when
needed.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
6dfb970d3d