Ensure that stream-based argument decoding can't go past the actual
end of the receive buffer. xdr_init_decode's calculation of the
value of xdr->end over-estimates the end of the buffer because the
Linux kernel RPC server code does not remove the size of the RPC
header from rqstp->rq_arg before calling the upper layer's
dispatcher.
The server-side still uses the svc_getnl() macros to decode the
RPC call header. These macros reduce the length of the head iov
but do not update the total length of the message in the buffer
(buf->len).
A proper fix for this would be to replace the use of svc_getnl() and
friends in the RPC header decoder, but that would be a large and
invasive change that would be difficult to backport.
Fixes: 5191955d6fc6 ("SUNRPC: Prepare for xdr_stream-style decoding on the server-side")
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
include/linux/sunrpc/svc.h | 14 +++++++++++---
include/linux/sunrpc/xdr.h | 12 ++++++++++++
2 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index daecb009c05b..494375313a6f 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -544,16 +544,24 @@ static inline void svc_reserve_auth(struct svc_rqst *rqstp, int space)
}
/**
- * svcxdr_init_decode - Prepare an xdr_stream for svc Call decoding
+ * svcxdr_init_decode - Prepare an xdr_stream for Call decoding
* @rqstp: controlling server RPC transaction context
*
+ * This function currently assumes the RPC header in rq_arg has
+ * already been decoded. Upon return, xdr->p points to the
+ * location of the upper layer header.
*/
static inline void svcxdr_init_decode(struct svc_rqst *rqstp)
{
struct xdr_stream *xdr = &rqstp->rq_arg_stream;
- struct kvec *argv = rqstp->rq_arg.head;
+ struct xdr_buf *buf = &rqstp->rq_arg;
+ struct kvec *argv = buf->head;
- xdr_init_decode(xdr, &rqstp->rq_arg, argv->iov_base, NULL);
+ /* Reset the argument buffer's length, now that the RPC header
+ * has been decoded. */
+ buf->len = xdr_buf_length(buf);
+
+ xdr_init_decode(xdr, buf, argv->iov_base, NULL);
xdr_set_scratch_page(xdr, rqstp->rq_scratch_page);
}
diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index 69175029abbb..f6bb215d4029 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -83,6 +83,18 @@ xdr_buf_init(struct xdr_buf *buf, void *start, size_t len)
buf->buflen = len;
}
+/**
+ * xdr_buf_length - Return the summed length of @buf's sub-buffers
+ * @buf: an instantiated xdr_buf
+ *
+ * Returns the sum of the lengths of the head kvec, the tail kvec,
+ * and the page array.
+ */
+static inline unsigned int xdr_buf_length(const struct xdr_buf *buf)
+{
+ return buf->head->iov_len + buf->page_len + buf->tail->iov_len;
+}
+
/*
* pre-xdr'ed macros.
*/
