On Fri, Aug 21, 2020 at 02:59:32PM -0400, Chuck Lever wrote:
> Oops. Short description should read:
>
> NFS: Fix listxattr receive buffer size
>
>
> > On Aug 21, 2020, at 1:36 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
> >
> > Certain NFSv4.2/RDMA tests fail with v5.9-rc1.
> >
> > rpcrdma_convert_kvec() runs off the end of the rl_segments array
> > because rq_rcv_buf.tail[0].iov_len holds a very large positive
> > value. The resultant kernel memory corruption is enough to crash
> > the client system.
> >
> > Callers of rpc_prepare_reply_pages() must reserve an extra XDR_UNIT
> > in the maximum decode size for a possible XDR pad of the contents
> > of the xdr_buf's pages. That guarantees the allocated receive buffer
> > will be large enough to accommodate the usual contents plus that XDR
> > pad word.
> >
> > encode_op_hdr() cannot add that extra word. If it does,
> > xdr_inline_pages() underruns the length of the tail iovec.
> >
> > Fixes: 3e1f02123fba ("NFSv4.2: add client side XDR handling for extended attributes")
> > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> > ---
> > fs/nfs/nfs42xdr.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/nfs/nfs42xdr.c b/fs/nfs/nfs42xdr.c
> > index cc50085e151c..d0ddf90c9be4 100644
> > --- a/fs/nfs/nfs42xdr.c
> > +++ b/fs/nfs/nfs42xdr.c
> > @@ -179,7 +179,7 @@
> > 1 + nfs4_xattr_name_maxsz + 1)
> > #define decode_setxattr_maxsz (op_decode_hdr_maxsz + decode_change_info_maxsz)
> > #define encode_listxattrs_maxsz (op_encode_hdr_maxsz + 2 + 1)
> > -#define decode_listxattrs_maxsz (op_decode_hdr_maxsz + 2 + 1 + 1)
> > +#define decode_listxattrs_maxsz (op_decode_hdr_maxsz + 2 + 1 + 1 + 1)
> > #define encode_removexattr_maxsz (op_encode_hdr_maxsz + 1 + \
> > nfs4_xattr_name_maxsz)
> > #define decode_removexattr_maxsz (op_decode_hdr_maxsz + \
> > @@ -504,7 +504,7 @@ static void encode_listxattrs(struct xdr_stream *xdr,
> > {
> > __be32 *p;
> >
> > - encode_op_hdr(xdr, OP_LISTXATTRS, decode_listxattrs_maxsz + 1, hdr);
> > + encode_op_hdr(xdr, OP_LISTXATTRS, decode_listxattrs_maxsz, hdr);
> >
> > p = reserve_space(xdr, 12);
> > if (unlikely(!p))
> >
> >
>
> --
> Chuck Lever
A detail of the sunrpc/xdr code I wasn't familiar with.. thanks for
fixing this.
- Frank
