Re: KASAN: use-after-free in __mutex_lock

Luiz Augusto von Dentz
2022-09-30T17:46:58Z

Hi Kim,

On Fri, Sep 30, 2022 at 9:09 AM Sungwoo Kim <iam@sung-woo.kim> wrote:
>
> Hi Dentz,
> How about to use l2cap_get_chan_by_scid because it looks resposible to
> handle ref_cnt.
>
> Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
> ---
> net/bluetooth/l2cap_core.c | 24 +++++++-----------------
> 1 file changed, 7 insertions(+), 17 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 2c9de67da..d3a074cbc 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -4291,26 +4291,18 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
> BT_DBG("dcid 0x%4.4x scid 0x%4.4x result 0x%2.2x status 0x%2.2x",
> dcid, scid, result, status);
>
> - mutex_lock(&conn->chan_lock);
> -
> if (scid) {
> - chan = __l2cap_get_chan_by_scid(conn, scid);
> - if (!chan) {
> - err = -EBADSLT;
> - goto unlock;
> - }
> + chan = l2cap_get_chan_by_scid(conn, scid);
> + if (!chan)
> + return -EBADSLT;
> } else {
> - chan = __l2cap_get_chan_by_ident(conn, cmd->ident);
> - if (!chan) {
> - err = -EBADSLT;
> - goto unlock;
> - }
> + chan = l2cap_get_chan_by_ident(conn, cmd->ident);
> + if (!chan)
> + return -EBADSLT;
> }
>
> err = 0;
>
> - l2cap_chan_lock(chan);
> -
> switch (result) {
> case L2CAP_CR_SUCCESS:
> l2cap_state_change(chan, BT_CONFIG);
> @@ -4336,9 +4328,7 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
> }
>
> l2cap_chan_unlock(chan);
> -
> -unlock:
> - mutex_unlock(&conn->chan_lock);
> + l2cap_chan_put(chan);
>
> return err;
> }
> --
> 2.25.1

Ive sent a fix yesterday:

https://patchwork.kernel.org/project/bluetooth/patch/20220929203241.4140795-1-luiz.dentz@gmail.com/

Both are sorta similar but the one above end up causing less code
changes which might be easier to backport.

--
Luiz Augusto von Dentz