sunrpc: fix xs_read_xdr_buf for partial pages receive

When receiving pages data, return value 'ret' when positive includes
`buf->page_base`, so we should subtract that before it is used for
changing `offset` and comparing against `want`.

This was discovered on the very rare cases where the server returned a
chunk of bytes that when added to the already received amount of bytes
for the pages happened to match the current `recv.len`, for example
on this case:

     buf->page_base : 258356
     actually received from socket: 1740
     ret : 260096
     want : 260096

In this case neither of the two 'if ... goto out' trigger, and we
continue to tail parsing.

Worth to mention that the ensuing EMSGSIZE from the continued execution of
`xs_read_xdr_buf` may be observed by an application due to 4 superfluous
bytes being added to the pages data.

Fixes: 277e4ab7d530 ("SUNRPC: Simplify TCP receive code by switching to using iterators")
Signed-off-by: Dan Aloni <dan@kernelim.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index c93ff70da3f983e8a61a4f4fda7ae3997bc3e2e9..c56a66cdf4ac80d8cab6cd72c90fd86155013e3b 100644 (file)
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -433,7 +433,8 @@ xs_read_xdr_buf(struct socket *sock, struct msghdr *msg, int flags,
                if (ret <= 0)
                        goto sock_err;
                xs_flush_bvec(buf->bvec, ret, seek + buf->page_base);
-               offset += ret - buf->page_base;
+               ret -= buf->page_base;
+               offset += ret;
                if (offset == count || msg->msg_flags & (MSG_EOR|MSG_TRUNC))
                        goto out;
                if (ret != want)