On 8/16/20 7:29 AM, Cong Wang wrote:
> __tipc_nl_compat_dumpit() has two callers, and it expects them to
> pass a valid nlmsghdr via arg->data. This header is artificial and
> crafted just for __tipc_nl_compat_dumpit().
>
> tipc_nl_compat_publ_dump() does so by putting a genlmsghdr as well
> as some nested attribute, TIPC_NLA_SOCK. But the other caller
> tipc_nl_compat_dumpit() does not, this leaves arg->data uninitialized
> on this call path.
>
> Fix this by just adding a similar nlmsghdr without any payload in
> tipc_nl_compat_dumpit().
>
> This bug exists since day 1, but the recent commit 6ea67769ff33
> ("net: tipc: prepare attrs in __tipc_nl_compat_dumpit()") makes it
> easier to appear.
>
> Reported-and-tested-by: syzbot+0e7181deafa7e0b79...@syzkaller.appspotmail.com
> Fixes: d0796d1ef63d ("tipc: convert legacy nl bearer dump to nl compat")
> Cc: Jon Maloy <jma...@redhat.com>
> Cc: Ying Xue <ying....@windriver.com>
> Cc: Richard Alpe <richard.a...@ericsson.com>
> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
Good finding and thanks to fix it!
Acked-by: Ying Xue <ying....@windriver.com>
> ---
> net/tipc/netlink_compat.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/net/tipc/netlink_compat.c b/net/tipc/netlink_compat.c
> index 217516357ef2..90e3c70a91ad 100644
> --- a/net/tipc/netlink_compat.c
> +++ b/net/tipc/netlink_compat.c
> @@ -275,8 +275,9 @@ static int __tipc_nl_compat_dumpit(struct
> tipc_nl_compat_cmd_dump *cmd,
> static int tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
> struct tipc_nl_compat_msg *msg)
> {
> - int err;
> + struct nlmsghdr *nlh;
> struct sk_buff *arg;
> + int err;
>
> if (msg->req_type && (!msg->req_size ||
> !TLV_CHECK_TYPE(msg->req, msg->req_type)))
> @@ -305,6 +306,15 @@ static int tipc_nl_compat_dumpit(struct
> tipc_nl_compat_cmd_dump *cmd,
> return -ENOMEM;
> }
>
> + nlh = nlmsg_put(arg, 0, 0, tipc_genl_family.id, 0, NLM_F_MULTI);
> + if (!nlh) {
> + kfree_skb(arg);
> + kfree_skb(msg->rep);
> + msg->rep = NULL;
> + return -EMSGSIZE;
> + }
> + nlmsg_end(arg, nlh);
> +
> err = __tipc_nl_compat_dumpit(cmd, msg, arg);
> if (err) {
> kfree_skb(msg->rep);
>
