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Date: Fri, 24 Aug 2018 18:02:25 -0700
From: John Fastabend <john.fastabend@...il.com>
To: Tushar Dave <tushar.n.dave@...cle.com>, ast@...nel.org,
daniel@...earbox.net, davem@...emloft.net,
sowmini.varadhan@...cle.com, santosh.shilimkar@...cle.com,
jakub.kicinski@...ronome.com, quentin.monnet@...ronome.com,
jiong.wang@...ronome.com, sandipan@...ux.vnet.ibm.com,
kafai@...com, rdna@...com, yhs@...com, netdev@...r.kernel.org
Subject: Re: [RFC v3 net-next 3/5] ebpf: fix bpf_msg_pull_data
On 08/17/2018 04:08 PM, Tushar Dave wrote:
> Like sockmap (sk_msg), socksg also deals with struct scatterlist
> therefore socksg programs can use existing bpf helper bpf_msg_pull_data
> to access packet data contained in struct scatterlist. While doing some
> prelimnary testing, there are couple of issues found with
> bpf_msg_pull_data that are fixed in this patch.
>
> Also, there cannot be more than MAX_SKB_FRAGS entries in sg_data
> therefore any checks for sg entry more than MAX_SKB_FRAGS in
> bpf_msg_pull_data() is removed.
In sockmap the scatterlist is used as a ring so the MAX_SKB_FRAGS
check is needed to keep searching through the ring when sg_start
is non-zero.
>
> Besides that, I also ran into issues while put_page() is invoked.
> e.g.
> [ 450.568723] BUG: Bad page state in process swapper/10 pfn:2021540
> [ 450.575632] page:ffffea0080855000 count:0 mapcount:0
> mapping:ffff88103d006840 index:0xffff882021540000 compound_mapcount: 0
> [ 450.588069] flags: 0x6fffff80008100(slab|head)
> [ 450.593033] raw: 006fffff80008100 dead000000000100 dead000000000200
> ffff88103d006840
> [ 450.601683] raw: ffff882021540000 0000000080080007 00000000ffffffff
> 0000000000000000
> [ 450.610337] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
> [ 450.617530] bad because of flags: 0x100(slab)
>
> To avoid above issue, currently put_page() is disabled in this patch
> temporarily. I am working on alternatives so that page allocated via
> slab (in this case) can be freed without any issue.>
> Signed-off-by: Tushar Dave <tushar.n.dave@...cle.com>
> Acked-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> ---
> net/core/filter.c | 61 +++++++++++++++++++++++++++++--------------------------
> 1 file changed, 32 insertions(+), 29 deletions(-)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index e427c8e..cc52baa 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2316,7 +2316,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
> BPF_CALL_4(bpf_msg_pull_data,
> struct sk_msg_buff *, msg, u32, start, u32, end, u64, flags)
> {
> - unsigned int len = 0, offset = 0, copy = 0;
> + unsigned int len = 0, offset = 0, copy = 0, off = 0;
> struct scatterlist *sg = msg->sg_data;
> int first_sg, last_sg, i, shift;
> unsigned char *p, *to, *from;
> @@ -2330,22 +2330,28 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
> i = msg->sg_start;
> do {
> len = sg[i].length;
> - offset += len;
> if (start < offset + len)
> break;
> + offset += len;
This looks like a generic fix unrelated to this series.
Can you send that as a bugfix?
> i++;
> - if (i == MAX_SKB_FRAGS)
> - i = 0;
> - } while (i != msg->sg_end);
> + } while (i <= msg->sg_end);
>
As noted above the MAX_SKB_FRAGS check is needed because
sg_start can be non-zero and sg_end < st_start. In these
cases we need to search the entries at the start of the
array (being used as a ring).
> + /* return error if start is out of range */
> if (unlikely(start >= offset + len))
> return -EINVAL;
>
> - if (!msg->sg_copy[i] && bytes <= len)
> - goto out;
> + /* return error if i is last entry in sglist and end is out of range */
> + if (msg->sg_copy[i] && end > offset + len)
> + return -EINVAL>
> first_sg = i;
>
> + /* if i is not last entry in sg list and end (i.e start + bytes) is
> + * within this sg[i] then goto out and calculate data and data_end
> + */
> + if (!msg->sg_copy[i] && end <= offset + len)
> + goto out;
> +> /* At this point we need to linearize multiple scatterlist
> * elements or a single shared page. Either way we need to
> * copy into a linear buffer exclusively owned by BPF. Then
> @@ -2359,11 +2365,14 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
> do {
> copy += sg[i].length;
> i++;
> - if (i == MAX_SKB_FRAGS)
> - i = 0;
same as above, need to keep.
> - if (bytes < copy)
> + if (end < copy)
> break;
> - } while (i != msg->sg_end);
> + } while (i <= msg->sg_end);
> +
> + /* return error if i is last entry in sglist and end is out of range */
> + if (i > msg->sg_end && end > offset + copy)
> + return -EINVAL;
> +
> last_sg = i;
>
> if (unlikely(copy < end - start))
> @@ -2373,23 +2382,25 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
> if (unlikely(!page))
> return -ENOMEM;
> p = page_address(page);
> - offset = 0;
>
> i = first_sg;
> do {
> from = sg_virt(&sg[i]);
> len = sg[i].length;
> - to = p + offset;
> + to = p + off;
Not really sure if the change from offset->off is needed. Looks
like it just makes a bigger diff.
>
> memcpy(to, from, len);
> - offset += len;
> + off += len;
> sg[i].length = 0;
> - put_page(sg_page(&sg[i]));
> + /* if original page is allocated via slab then put_page
> + * causes error BUG: Bad page state in process. So temporarily
> + * disabled put_page.
> + * Todo: fix it
> + */
> + //put_page(sg_page(&sg[i]));
>
> i++;
> - if (i == MAX_SKB_FRAGS)
> - i = 0;
> - } while (i != last_sg);
> + } while (i < last_sg);
>
> sg[first_sg].length = copy;
> sg_set_page(&sg[first_sg], page, copy, 0);
> @@ -2406,12 +2417,8 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
> do {
> int move_from;
>
> - if (i + shift >= MAX_SKB_FRAGS)
> - move_from = i + shift - MAX_SKB_FRAGS;
> - else
> - move_from = i + shift;
> -
Need to keep same as above.
> - if (move_from == msg->sg_end)
> + move_from = i + shift;> + if (move_from > msg->sg_end)
> break;
>
> sg[i] = sg[move_from];
> @@ -2420,14 +2427,10 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
> sg[move_from].offset = 0;
>
> i++;
> - if (i == MAX_SKB_FRAGS)
> - i = 0;
> } while (1);
> msg->sg_end -= shift;
> - if (msg->sg_end < 0)
> - msg->sg_end += MAX_SKB_FRAGS;
> out:
> - msg->data = sg_virt(&sg[i]) + start - offset;
> + msg->data = sg_virt(&sg[first_sg]) + start - offset;
> msg->data_end = msg->data + bytes;
>
> return 0;
>
Thanks,
John
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