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Date: Thu, 30 Aug 2018 09:20:31 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Tushar Dave <tushar.n.dave@...cle.com>, john.fastabend@...il.com,
ast@...nel.org, davem@...emloft.net, netdev@...r.kernel.org
Cc: sowmini.varadhan@...cle.com
Subject: Re: [PATCH net] ebpf: fix bpf_msg_pull_data
On 08/30/2018 02:21 AM, Tushar Dave wrote:
> On 08/29/2018 05:07 PM, Tushar Dave wrote:
>> While doing some preliminary testing it is found that bpf helper
>> bpf_msg_pull_data does not calculate the data and data_end offset
>> correctly. Fix it!
>>
>> Fixes: 015632bb30da ("bpf: sk_msg program helper bpf_sk_msg_pull_data")
>> Signed-off-by: Tushar Dave <tushar.n.dave@...cle.com>
>> Acked-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
>> ---
>> net/core/filter.c | 38 +++++++++++++++++++++++++-------------
>> 1 file changed, 25 insertions(+), 13 deletions(-)
>>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index c25eb36..3eeb3d6 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -2285,7 +2285,7 @@ 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;
>> @@ -2299,22 +2299,30 @@ 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;
>> i++;
>> if (i == MAX_SKB_FRAGS)
>> i = 0;
>> - } while (i != msg->sg_end);
>> + } while (i <= msg->sg_end);
I don't think this condition is correct, msg operates as a scatterlist ring,
so sg_end may very well be < current i when there's a wrap-around in the
traversal ... more below.
>> + /* 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
>> @@ -2330,9 +2338,14 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>> i++;
>> if (i == MAX_SKB_FRAGS)
>> i = 0;
>> - 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))
>> @@ -2342,23 +2355,22 @@ 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;
>> memcpy(to, from, len);
>> - offset += len;
>> + off += len;
>> sg[i].length = 0;
>> 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);
>> @@ -2380,7 +2392,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>> else
>> move_from = i + shift;
>> - if (move_from == msg->sg_end)
>> + if (move_from > msg->sg_end)
>> break;
>> sg[i] = sg[move_from];
>> @@ -2396,7 +2408,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
>> 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;
>>
>
> Please discard this patch. I just noticed that Daniel Borkmann sent some similar fixes for bpf_msg_pull_data.
Yeah I've been looking at these recently as well, please make sure you test
with the below fixes included to see if there's anything left:
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/net/core/filter.c?id=5b24109b0563d45094c470684c1f8cea1af269f8
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/net/core/filter.c?id=0e06b227c5221dd51b5569de93f3b9f532be4a32
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/net/core/filter.c?id=2e43f95dd8ee62bc8bf57f2afac37fbd70c8d565
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/net/core/filter.c?id=a8cf76a9023bc6709b1361d06bb2fae5227b9d68
Thanks,
Daniel
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