From: Jesper Dangaard Brouer Date: Thu, 19 Apr 2018 14:17:12 +0000 (+0200) Subject: bpf: reserve xdp_frame size in xdp headroom X-Git-Tag: for-linus-20180616~56^2~417^2~2 X-Git-Url: https://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff_plain;h=97e19cce05e50055dafd1df71bdcbcdc3a7894c5 bpf: reserve xdp_frame size in xdp headroom Commit 6dfb970d3dbd ("xdp: avoid leaking info stored in frame data on page reuse") tried to allow user/bpf_prog to (re)use area used by xdp_frame (stored in frame headroom), by memset clearing area when bpf_xdp_adjust_head give bpf_prog access to headroom area. The mentioned commit had two bugs. (1) Didn't take bpf_xdp_adjust_meta into account. (2) a combination of bpf_xdp_adjust_head calls, where xdp->data is moved into xdp_frame section, can cause clearing xdp_frame area again for area previously granted to bpf_prog. After discussions with Daniel, we choose to implement a simpler solution to the problem, which is to reserve the headroom used by xdp_frame info. This also avoids the situation where bpf_prog is allowed to adjust/add headers, and then XDP_REDIRECT later drops the packet due to lack of headroom for the xdp_frame. This would likely confuse the end-user. Fixes: 6dfb970d3dbd ("xdp: avoid leaking info stored in frame data on page reuse") Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Daniel Borkmann --- diff --git a/net/core/filter.c b/net/core/filter.c index 29318598fd60..e25bc4a3aa1a 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2694,20 +2694,13 @@ 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_start = xdp_frame_end + metalen; void *data = xdp->data + offset; if (unlikely(data < data_start || 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); @@ -2751,12 +2744,13 @@ static const struct bpf_func_proto bpf_xdp_adjust_tail_proto = { BPF_CALL_2(bpf_xdp_adjust_meta, struct xdp_buff *, xdp, int, offset) { + void *xdp_frame_end = xdp->data_hard_start + sizeof(struct xdp_frame); void *meta = xdp->data_meta + offset; unsigned long metalen = xdp->data - meta; if (xdp_data_meta_unsupported(xdp)) return -ENOTSUPP; - if (unlikely(meta < xdp->data_hard_start || + if (unlikely(meta < xdp_frame_end || meta > xdp->data)) return -EINVAL; if (unlikely((metalen & (sizeof(__u32) - 1)) ||