Hi Dean,
* Dean Jenkins <djenkins@xxxxxxxxxx> [2012-08-11 19:47:10 +0100]:
> A race condition exists between near simultaneous asynchronous
> DLC data channel disconnection requests from the host and remote device.
> This causes the socket layer to request a socket shutdown at the same time
> the rfcomm core is processing the disconnect request from the remote
> device.
>
> The socket layer retains a copy of a struct rfcomm_dlc d pointer.
> The d pointer refers to a copy of a struct rfcomm_session.
> When the socket layer thread performs a socket shutdown, the thread
> may wait on a rfcomm lock in rfcomm_dlc_close(). This means that
> whilst the thread waits, the rfcomm_session and/or rfcomm_dlc structures
> pointed to by d maybe freed due to rfcomm core handling. Consequently,
> when the rfcomm lock becomes available and the thread runs, a
> malfunction could occur as a freed rfcomm_session pointer and/or a
> freed d pointer will be erroneously reused.
>
> Therefore, after the rfcomm lock is acquired, check that the struct
> rfcomm_session is still valid by searching the rfcomm session list.
> If the session is valid then validate the d pointer by searching the
> rfcomm session list of active DLCs for the rfcomm_dlc structure
> pointed by d.
>
> If active DLCs exist when the rfcomm session is terminating,
> avoid a memory leak of rfcomm_dlc structures by ensuring that
> rfcomm_session_close() is used instead of rfcomm_session_del().
>
> Signed-off-by: Dean Jenkins <djenkins@xxxxxxxxxx>
> ---
> net/bluetooth/rfcomm/core.c | 29 ++++++++++++++++++++++++++---
> 1 file changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
> index c7921fd..1a7db34 100644
> --- a/net/bluetooth/rfcomm/core.c
> +++ b/net/bluetooth/rfcomm/core.c
> @@ -496,11 +496,34 @@ static int __rfcomm_dlc_close(struct rfcomm_dlc *d, int err)
>
> int rfcomm_dlc_close(struct rfcomm_dlc *d, int err)
> {
> - int r;
> + int r = 0;
> + struct rfcomm_dlc *d_list;
> + struct rfcomm_session *s, *s_list;
> + struct list_head *p, *n, *p2, *n2;
>
> rfcomm_lock();
>
> - r = __rfcomm_dlc_close(d, err);
> + s = d->session;
> + if (s) {
Please invert the check here, and add a goto unlock;. There too many
indentation levels here.
> + /* check the session still exists after waiting on the mutex */
> + list_for_each_safe(p, n, &session_list) {
> + s_list = list_entry(p, struct rfcomm_session, list);
please use list_for_each_entry(), the _safe version seems to not be needed.
> + if (s == s_list) {
> + /* check the dlc still exists */
> + /* after waiting on the mutex */
> + list_for_each_safe(p2, n2, &s->dlcs) {
> + d_list = list_entry(p2,
> + struct rfcomm_dlc,
> + list);
and here you can use rfcomm_dlc_get()
Gustavo
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