[PATCH 5.19 195/717] SUNRPC: Fix svcxdr_init_decodes end-of-buffer calculation

Greg Kroah-Hartman
2022-10-22T07:56:55Z

From: Chuck Lever <chuck.lever@oracle.com>

[ Upstream commit 90bfc37b5ab91c1a6165e3e5cfc49bf04571b762 ]

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")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/sunrpc/svc.h | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index daecb009c05b..5a830b66f059 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -544,16 +544,27 @@ 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);
+ /*
+ * svc_getnl() and friends do not keep the xdr_buf's ::len
+ * field up to date. Refresh that field before initializing
+ * the argument decoding stream.
+ */
+ buf->len = buf->head->iov_len + buf->page_len + buf->tail->iov_len;
+
+ xdr_init_decode(xdr, buf, argv->iov_base, NULL);
xdr_set_scratch_page(xdr, rqstp->rq_scratch_page);
}

--
2.35.1