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    Subject[PATCH 4.14 03/91] tipc: fix uninit skb->data in tipc_nl_compat_dumpit()
    Date
    From: Cong Wang <xiyou.wangcong@gmail.com>

    [ Upstream commit 47733f9daf4fe4f7e0eb9e273f21ad3a19130487 ]

    __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+0e7181deafa7e0b79923@syzkaller.appspotmail.com
    Fixes: d0796d1ef63d ("tipc: convert legacy nl bearer dump to nl compat")
    Cc: Jon Maloy <jmaloy@redhat.com>
    Cc: Ying Xue <ying.xue@windriver.com>
    Cc: Richard Alpe <richard.alpe@ericsson.com>
    Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
    Acked-by: Ying Xue <ying.xue@windriver.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/tipc/netlink_compat.c | 12 +++++++++++-
    1 file changed, 11 insertions(+), 1 deletion(-)

    --- a/net/tipc/netlink_compat.c
    +++ b/net/tipc/netlink_compat.c
    @@ -250,8 +250,9 @@ err_out:
    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)))
    @@ -280,6 +281,15 @@ static int tipc_nl_compat_dumpit(struct
    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);

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