On Mon, Apr 14, 2008 at 03:55:16PM -0400, Chuck Lever wrote:
> On Apr 14, 2008, at 2:38 PM, J. Bruce Fields wrote:
>> On Mon, Apr 14, 2008 at 12:27:23PM -0400, Chuck Lever wrote:
>>> Clean up: ensure svc_udp_recvfrom() is getting at least a full UDP
>>> header
>>> to avoid potential negative intermediate values.
>>
>> Is it legal in this case for skb_recv_datagram() to return an skb
>> without at least that minimum length? (And if not, should this be a
>> BUG()?)
>>
>>
>>> A similar sanity check is already used in the RPC client.
>>
>> This one?:
>>
>> repsize = skb->len - sizeof(struct udphdr);
>> if (repsize < 4) {
>> dprintk("RPC: impossible RPC reply size %d!\n", repsize);
>> goto dropit;
>> }
>>
>> I assumed it was needed because of the rpc-level check (for the 4
>> bytes worth
>> of xid), not because it needed udp-level checking.
>
> The server side check programmatically guarantees we get a non-negative
> number when we compute "bytes."
Would a BUG() accomplish the same thing?
--b.
> Thus we can use an unsigned variable and
> eliminate a mixed sign comparison later on.
>
> We can add a "+ sizeof(u32)" to the check if you like.
>
>>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>> ---
>>>
>>> net/sunrpc/svcsock.c | 20 +++++++++++++-------
>>> 1 files changed, 13 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
>>> index d077071..de29e7f 100644
>>> --- a/net/sunrpc/svcsock.c
>>> +++ b/net/sunrpc/svcsock.c
>>> @@ -431,6 +431,7 @@ static int svc_udp_recvfrom(struct svc_rqst
>>> *rqstp)
>>> } buffer;
>>> struct cmsghdr *cmh = &buffer.hdr;
>>> int err, len;
>>> + unsigned int bytes;
>>> struct msghdr msg = {
>>> .msg_name = svc_addr(rqstp),
>>> .msg_control = cmh,
>>> @@ -484,8 +485,13 @@ static int svc_udp_recvfrom(struct svc_rqst
>>> *rqstp)
>>> */
>>> svc_xprt_received(&svsk->sk_xprt);
>>>
>>> - len = skb->len - sizeof(struct udphdr);
>>> - rqstp->rq_arg.len = len;
>>> + if (skb->len < sizeof(struct udphdr)) {
>>> + dprintk("svc: bad UDP datagram length: %u\n", skb->len);
>>> + skb_free_datagram(svsk->sk_sk, skb);
>>> + return 0;
>>> + }
>>> + bytes = skb->len - sizeof(struct udphdr);
>>> + rqstp->rq_arg.len = bytes;
>>>
>>> rqstp->rq_prot = IPPROTO_UDP;
>>>
>>> @@ -515,7 +521,7 @@ static int svc_udp_recvfrom(struct svc_rqst
>>> *rqstp)
>>> /* we can use it in-place */
>>> rqstp->rq_arg.head[0].iov_base = skb->data +
>>> sizeof(struct udphdr);
>>> - rqstp->rq_arg.head[0].iov_len = len;
>>> + rqstp->rq_arg.head[0].iov_len = bytes;
>>> if (skb_checksum_complete(skb)) {
>>> skb_free_datagram(svsk->sk_sk, skb);
>>> return 0;
>>> @@ -524,12 +530,12 @@ static int svc_udp_recvfrom(struct svc_rqst
>>> *rqstp)
>>> }
>>>
>>> rqstp->rq_arg.page_base = 0;
>>> - if (len <= rqstp->rq_arg.head[0].iov_len) {
>>> - rqstp->rq_arg.head[0].iov_len = len;
>>> + if (bytes <= rqstp->rq_arg.head[0].iov_len) {
>>> + rqstp->rq_arg.head[0].iov_len = bytes;
>>> rqstp->rq_arg.page_len = 0;
>>> rqstp->rq_respages = rqstp->rq_pages+1;
>>> } else {
>>> - rqstp->rq_arg.page_len = len - rqstp->rq_arg.head[0].iov_len;
>>> + rqstp->rq_arg.page_len = bytes - rqstp->rq_arg.head[0].iov_len;
>>> rqstp->rq_respages = rqstp->rq_pages + 1 +
>>> DIV_ROUND_UP(rqstp->rq_arg.page_len, PAGE_SIZE);
>>> }
>>> @@ -537,7 +543,7 @@ static int svc_udp_recvfrom(struct svc_rqst
>>> *rqstp)
>>> if (serv->sv_stats)
>>> serv->sv_stats->netudpcnt++;
>>>
>>> - return len;
>>> + return bytes;
>>> }
>>>
>>> static int
>>>
>
> --
> Chuck Lever
> chuck[dot]lever[at]oracle[dot]com
>
>
>
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