Re: [PATCH] SUNRPC: Fix another issue with MIC buffer space

[Chuck Lever <chuck.lever@oracle.com>]

> On Nov 15, 2019, at 9:35 AM, Benjamin Coddington <bcodding@redhat.com> wrote:
> 
> On 15 Nov 2019, at 8:39, Chuck Lever wrote:
> 
>> xdr_shrink_pagelen() BUG's when @len is larger than buf->page_len.
>> This can happen when xdr_buf_read_mic() is given an xdr_buf with
>> a small page array (like, only a few bytes).
> 
> Hi Chuck,
> 
> Seems like a bug in xdr_buf_read_mic to me, but I'm not seeing how this can
> happen.. unless perhaps xdr->page_len is 0?  Or maybe xdr_shift_buf has bug?

rpc_prepare_reply_pages() sets buf->page_len to the args->count of the
NFS READ request. For really small READs, this can be 2, or 12, or
anything smaller than the MIC length.


> I'd prefer to keep the BUG_ON.

Linus would prefer not to. :-)


> How can I reproduce it?

I've been using the git regression suite with NFSv4.1 and krb5i.
I run it with 12 threads.


> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index 14ba9e72a204..71d754fc780e 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -1262,6 +1262,8 @@ int xdr_buf_read_mic(struct xdr_buf *buf, struct xdr_netobj *mic, unsigned int o
>        if (offset < boundary && (offset + mic->len) > boundary)
>                xdr_shift_buf(buf, boundary - offset);
> 
> +       trace_printk("boundary %d, offset %d, page_len %d\n", boundary, offset, buf->page_len);
> +
>        /* Is the mic partially in the pages? */
>        boundary += buf->page_len;
>        if (offset < boundary && (offset + mic->len) > boundary)
> 
> ^^ that should be enough for me to try to figure out what's doing wrong.
> 
> Ben
> 

--
Chuck Lever