Re: [PATCH v3] Bluetooth: ISO: fix use-after-free of listener socket in iso_conn_ready

Hi Hang,

On Tue, Aug 18, 2026 at 7:33 AM Hang Nan <[email protected]> wrote:
>
> iso_conn_ready() looks up the BIS listener socket with iso_get_sock(),
> which takes a reference, and then, without re-checking its state,
> creates a child socket from it:
>
>     parent = iso_get_sock(hdev, ...);
>     if (!parent)
>         return;
>
>     lock_sock(parent);
>     sk = iso_sock_alloc(sock_net(parent), NULL, BTPROTO_ISO, ...);
>     ...
>     iso_chan_add(conn, sk, parent);
>     ...
>     release_sock(parent);
>     sock_put(parent);
>
> If the listener socket is closed concurrently, between iso_get_sock()
> and lock_sock(), the reference taken by iso_get_sock() may be the last
> one: the close path drops the link-list reference, and once
> iso_conn_ready() drops its own reference at the end of the function the
> socket is freed.  The child socket, however, is already linked to the
> freed parent, and a later disconnect of the child runs iso_chan_del()
> -> bt_accept_unlink(), which dereferences the dangling parent pointer
> into the freed accept queue (a use-after-free).  The same dangling
> pointer is also dereferenced through parent->***() in
> iso_chan_del().
>
> Fix it the same way the connected (non-BIS) path was fixed in commit
> 0d255e63fcf3 ("Bluetooth: ISO: hold sk properly in iso_conn_ready"):
> after taking the socket lock, re-check that the parent is still a
> listening, alive socket, and bail out otherwise.
>
> Fixes: ccf74f2390d60 ("Bluetooth: Add BTPROTO_ISO socket type")
> Cc: [email protected]
> Signed-off-by: Hang Nan <[email protected]>
> ---
> Changes in v3:
> - Move the changelog below the "---" separator so it is not part
>   of the commit message
> - Shorten the comment in iso_conn_ready()
>
> Changes in v2:
> - Fix GitLint B3: replace hard tabs with spaces in the commit
>   message code snippet (no functional change)
>
>  net/bluetooth/iso.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
> index aa2ce78f56a2..069fc87a4e18 100644
> --- a/net/bluetooth/iso.c
> +++ b/net/bluetooth/iso.c
> @@ -2277,6 +2277,14 @@ static void iso_conn_ready(struct iso_conn *conn)
>
>                 lock_sock(parent);
>
> +               /* The listener may have been closed concurrently. */
> +               if (parent->sk_state != BT_LISTEN ||
> +                   (parent, SOCK_ZAPPED)) {
> +                       release_sock_flagsock(parent);
> +                       sock_put(parent);
> +                       return;
> +               }

Looks like there is a typo and this should have been release_sock
rather than release_sock_flagsock (or there is a new function called
that introduced via some other tree?)

>                 sk = iso_sock_alloc(sock_net(parent), NULL,
>                                     BTPROTO_ISO, GFP_ATOMIC, 0);
>                 if (!sk) {
>


-- 
Luiz Augusto von Dentz