On Fri, Jan 26, 2018 at 1:23 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
>
>> On Jan 26, 2018, at 9:24 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>
>> Hi Bruce/Chuck,
>>
>> There is a problem with nfsd doing a WRITE of size 4093,4094,4095. To
>> reproduce, mount with RDMA and do a simple dd "dd if=/dev/zero
>> of=/mnt/testfile bs=4093 count=1". What happens is that nfsd fails to
>> parse GETATTR after the WRITE in the compound. It fails the operation
>> with ERR_OP_ILLEGAL.
>>
>> The problem happens for the values where XDR round up ends up rounding
>> up to the page size. I don't know if my fix is the appropriate way to
>> fix this but with it I don't get the error:
>>
>> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
>> index 2c61c6b..a8489c3 100644
>> --- a/fs/nfsd/nfs4xdr.c
>> +++ b/fs/nfsd/nfs4xdr.c
>> @@ -1289,11 +1289,12 @@ static __be32 nfsd4_decode_opaque(struct nfsd4_compounda
>>
>> len = XDR_QUADLEN(write->wr_buflen) << 2;
>> if (len >= avail) {
>> - int pages;
>> + int pages = 0;
>>
>> len -= avail;
>>
>> - pages = len >> PAGE_SHIFT;
>> + if (write->wr_buflen >= PAGE_SIZE)
>> + pages = len >> PAGE_SHIFT;
>> argp->pagelist += pages;
>> argp->pagelen -= pages * PAGE_SIZE;
>> len -= pages * PAGE_SIZE;
>>
>> So the problem is the using "len" instead of "write->wr_buflen" leads
>> for the values 4093,4094,4095 that are rounded up to 4096, it makes
>> pages=1 and the argp->pagelen ends up being a negative value leading
>> to problems of parsing the GETATTR.
>
> Would this also be a problem near any page boundary, say, a
> write length of 8191 bytes?
>
> Instead of using the rounded up "len", why not try this:
>
> - pages = len >> PAGE_SHIFT;
> + pages = write->wr_buflen >> PAGE_SHIFT;
You are right. It needs to be that. Otherwise 8191 fails the same way.
> And be sure to test with TCP as well.
Sigh. It breaks normal (non-RDMA) mounts. I'll figure out why.
>> If this looks OK, I can send a patch.
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>
> --
> Chuck Lever
>
>
>
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