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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, syzbot+5ec223ccb83b24ef982f@syzkaller.appspotmail.com, shuvampandey1@gmail.com Subject: [PATCH net v2] atm: mpoa: keep mpc->dev referenced across mpoad restart Date: Sat, 11 Apr 2026 17:44:58 +0545 Message-ID: <20260411115958.64827-1-shuvampandey1@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit atm: mpoa: keep mpc->dev referenced across mpoad restart syzbot reported a netdevice refcount warning: refcount_t: decrement hit 0; leaking memory. WARNING: lib/refcount.c:31 at refcount_warn_saturate+0x70/0x110 ... dev_put include/linux/netdevice.h:4466 [inline] mpoad_close+0x1fc/0x3e0 net/atm/mpc.c:889 mpoad_close() drops the reference held in mpc->dev, but the mpoa_client itself stays alive and keeps the same device pointer. When mpoad is attached again, atm_mpoa_mpoad_attach() reuses the existing mpoa_client and its mpc->dev without reacquiring that reference, so the next close can hit the netdevice refcount warning. This reference is owned by the mpoa_client/LEC association rather than a single mpoad open/close cycle. It is acquired when the client gets its LEC device and is released later from mpoa_event_listener() on NETDEV_UNREGISTER. Fix the imbalance by removing the dev_put() from mpoad_close(). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+5ec223ccb83b24ef982f@syzkaller.appspotmail.com Link: https://groups.google.com/g/syzkaller-bugs/c/qhZ5MJfLBOE/m/UnotmgRdAQAJ Signed-off-by: Shuvam Pandey --- Changes in v2: - drop the atm_mpoa_cleanup() dev_put()/NULL hunk - add the syzbot warning excerpt - add a Fixes tag - clarify that the final dev_put() comes from the notifier path net/atm/mpc.c | 1 - 1 file changed, 1 deletion(-) diff --git a/net/atm/mpc.c b/net/atm/mpc.c index ce8e9780373b9..90ab8f2889734 100644 --- a/net/atm/mpc.c +++ b/net/atm/mpc.c @@ -886,7 +886,6 @@ static void mpoad_close(struct atm_vcc *vcc) struct lec_priv *priv = netdev_priv(mpc->dev); priv->lane2_ops->associate_indicator = NULL; stop_mpc(mpc); - dev_put(mpc->dev); } mpc->in_ops->destroy_cache(mpc);