[PATCH] Tools: hv: correct payload size in netlink_send

[PATCH] Tools: hv: correct payload size in netlink_send

[Olaf Hering]

netlink_send is supposed to send just the cn_msg+hv_kvp_msg via netlink.
Currently it sets an incorrect iovec size, as reported by valgrind.

In the case of registering with the kernel the allocated buffer is large
enough to hold nlmsghdr+cn_msg+hv_kvp_msg, no overrun happens. In the
case of responding to the kernel the cn_msg is located in the middle of
recv_buffer, after the nlmsghdr. Currently the code in netlink_send adds
also the size of nlmsghdr to the payload. But nlmsghdr is a separate
iovec. This leads to an (harmless) out-of-bounds access when the kernel
processes the iovec. Correct the iovec size of the cn_msg to be just
cn_msg + its payload.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 tools/hv/hv_kvp_daemon.c | 2 +-
 tools/hv/hv_vss_daemon.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/hv/hv_kvp_daemon.c b/tools/hv/hv_kvp_daemon.c
index d3bcb84..1bd1ad1 100644
--- a/tools/hv/hv_kvp_daemon.c
+++ b/tools/hv/hv_kvp_daemon.c
@@ -1399,7 +1399,7 @@ netlink_send(int fd, struct cn_msg *msg)
 	char buffer[64];
 	struct iovec iov[2];
 
-	size = NLMSG_SPACE(sizeof(struct cn_msg) + msg->len);
+	size = sizeof(struct cn_msg) + msg->len;
 
 	nlh = (struct nlmsghdr *)buffer;
 	nlh->nlmsg_seq = 0;
diff --git a/tools/hv/hv_vss_daemon.c b/tools/hv/hv_vss_daemon.c
index 6b4f2fa..2f1f53f 100644
--- a/tools/hv/hv_vss_daemon.c
+++ b/tools/hv/hv_vss_daemon.c
@@ -111,7 +111,7 @@ static int netlink_send(int fd, struct cn_msg *msg)
 	char buffer[64];
 	struct iovec iov[2];
 
-	size = NLMSG_SPACE(sizeof(struct cn_msg) + msg->len);
+	size = sizeof(struct cn_msg) + msg->len;
 
 	nlh = (struct nlmsghdr *)buffer;
 	nlh->nlmsg_seq = 0;

RE: [PATCH] Tools: hv: correct payload size in netlink_send

[KY Srinivasan]

> -----Original Message-----
> From: Olaf Hering [mailto:olaf@aepfle.de]
> Sent: Wednesday, August 07, 2013 9:07 AM
> To: KY Srinivasan; gregkh@linuxfoundation.org
> Cc: linux-kernel@vger.kernel.org; Olaf Hering
> Subject: [PATCH] Tools: hv: correct payload size in netlink_send
> 
> netlink_send is supposed to send just the cn_msg+hv_kvp_msg via netlink.
> Currently it sets an incorrect iovec size, as reported by valgrind.
> 
> In the case of registering with the kernel the allocated buffer is large
> enough to hold nlmsghdr+cn_msg+hv_kvp_msg, no overrun happens. In the
> case of responding to the kernel the cn_msg is located in the middle of
> recv_buffer, after the nlmsghdr. Currently the code in netlink_send adds
> also the size of nlmsghdr to the payload. But nlmsghdr is a separate
> iovec. This leads to an (harmless) out-of-bounds access when the kernel
> processes the iovec. Correct the iovec size of the cn_msg to be just
> cn_msg + its payload.

Thanks Olaf.

> 
> Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>

> ---
>  tools/hv/hv_kvp_daemon.c | 2 +-
>  tools/hv/hv_vss_daemon.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/hv/hv_kvp_daemon.c b/tools/hv/hv_kvp_daemon.c
> index d3bcb84..1bd1ad1 100644
> --- a/tools/hv/hv_kvp_daemon.c
> +++ b/tools/hv/hv_kvp_daemon.c
> @@ -1399,7 +1399,7 @@ netlink_send(int fd, struct cn_msg *msg)
>  	char buffer[64];
>  	struct iovec iov[2];
> 
> -	size = NLMSG_SPACE(sizeof(struct cn_msg) + msg->len);
> +	size = sizeof(struct cn_msg) + msg->len;
> 
>  	nlh = (struct nlmsghdr *)buffer;
>  	nlh->nlmsg_seq = 0;
> diff --git a/tools/hv/hv_vss_daemon.c b/tools/hv/hv_vss_daemon.c
> index 6b4f2fa..2f1f53f 100644
> --- a/tools/hv/hv_vss_daemon.c
> +++ b/tools/hv/hv_vss_daemon.c
> @@ -111,7 +111,7 @@ static int netlink_send(int fd, struct cn_msg *msg)
>  	char buffer[64];
>  	struct iovec iov[2];
> 
> -	size = NLMSG_SPACE(sizeof(struct cn_msg) + msg->len);
> +	size = sizeof(struct cn_msg) + msg->len;
> 
>  	nlh = (struct nlmsghdr *)buffer;
>  	nlh->nlmsg_seq = 0;