> 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;
And be sure to test with TCP as well.
> If this looks OK, I can send a patch.
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--
Chuck Lever
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