On 13 Sep 2019, at 10:41, Chuck Lever wrote:
On Sep 12, 2019, at 1:07 PM, Benjamin Coddington
<bcodding@xxxxxxxxxx> wrote:
The GSS Message Integrity Check data for krb5i may lie partially in
the XDR
reply buffer's pages and tail. If so, we try to copy the entire MIC
into
free space in the tail. But as the estimations of the slack space
required
for authentication and verification have improved there may be less
free
space in the tail to complete this copy -- see commit 2c94b8eca1a2
("SUNRPC: Use au_rslack when computing reply buffer size"). In fact,
there
may only be room in the tail for a single copy of the MIC, and not
part of
the MIC and then another complete copy.
The real world failure reported is that `ls` of a directory on NFS
may
sometimes return -EIO, which can be traced back to
xdr_buf_read_netobj()
failing to find available free space in the tail to copy the MIC.
Fix this by checking for the case of the MIC crossing the boundaries
of
head, pages, and tail. If so, shift the buffer until the MIC is
contained
completely within the pages or tail. This allows the remainder of
the
function to create a sub buffer that directly address the complete
MIC.
Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
# v5.1 ?
That makes sense to match the changes to rslack.
---
net/sunrpc/xdr.c | 45 +++++++++++++++++++++++++++------------------
1 file changed, 27 insertions(+), 18 deletions(-)
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 48c93b9e525e..6e05a9693568 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -1237,39 +1237,48 @@ xdr_encode_word(struct xdr_buf *buf, unsigned
int base, u32 obj)
EXPORT_SYMBOL_GPL(xdr_encode_word);
/* If the netobj starting offset bytes from the start of xdr_buf is
contained
- * entirely in the head or the tail, set object to point to it;
otherwise
- * try to find space for it at the end of the tail, copy it there,
and
- * set obj to point to it. */
+ * entirely in the head, pages, or tail, set object to point to it;
otherwise
+ * shift the buffer until it is contained entirely within the pages
or tail.
+ */
int xdr_buf_read_netobj(struct xdr_buf *buf, struct xdr_netobj *obj,
unsigned int offset)
{
struct xdr_buf subbuf;
+ unsigned int len_to_boundary;
if (xdr_decode_word(buf, offset, &obj->len))
return -EFAULT;
- if (xdr_buf_subsegment(buf, &subbuf, offset + 4, obj->len))
+
+ offset += 4;
+
+ /* Is the obj partially in the head? */
+ len_to_boundary = buf->head->iov_len - offset;
+ if (len_to_boundary > 0 && len_to_boundary < obj->len)
+ xdr_shift_buf(buf, len_to_boundary);
+
+ /* Is the obj partially in the pages? */
+ len_to_boundary = buf->head->iov_len + buf->page_len - offset;
+ if (len_to_boundary > 0 && len_to_boundary < obj->len)
+ xdr_shrink_pagelen(buf, len_to_boundary);
Do you need to check if the obj is entirely in ->pages but crosses a
page boundary?
We're going to copy it out into the tail in that case. I'm assuming
read_bytes_from_xdr_buf() can handle reading across page boundaries.
So unless I'm missing something, I don't think we need to check.
Ben
