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

["Benjamin Coddington" <bcodding@redhat.com>]

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?

I'd prefer to keep the BUG_ON.  How can I reproduce it?

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