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xdp: avoid leaking info stored in frame data on page reuse

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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>
This commit is contained in:
Jesper Dangaard Brouer 2018-04-17 16:46:43 +02:00 committed by David S. Miller
parent 44fa2dbd47
commit 6dfb970d3d
1 changed files with 8 additions and 0 deletions
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8
net/core/filter.c
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@ -2692,6 +2692,7 @@ static unsigned long xdp_get_metalen(const struct xdp_buff *xdp)
BPF_CALL_2(bpf_xdp_adjust_head, struct xdp_buff *, xdp, int, offset)
{
void *xdp_frame_end = xdp->data_hard_start + sizeof(struct xdp_frame);
unsigned long metalen = xdp_get_metalen(xdp);
void *data_start = xdp->data_hard_start + metalen;
void *data = xdp->data + offset;
@ -2700,6 +2701,13 @@ BPF_CALL_2(bpf_xdp_adjust_head, struct xdp_buff *, xdp, int, offset)
data > xdp->data_end - ETH_HLEN))
return -EINVAL;
/* Avoid info leak, when reusing area prev used by xdp_frame */
if (data < xdp_frame_end) {
unsigned long clearlen = xdp_frame_end - data;
memset(data, 0, clearlen);
}
if (metalen)
memmove(xdp->data_meta + offset,
xdp->data_meta, metalen);