From c78a4e41ab5ead6193ad8a2dd92e8906bae659fa Mon Sep 17 00:00:00 2001 From: Fan Wu Date: Wed, 17 Jun 2026 02:05:18 +0000 Subject: [PATCH] hdlc_ppp: sync per-proto timers before freeing hdlc state Each PPP control protocol (LCP/IPCP/IPV6CP) embedded in struct ppp registers a timer via timer_setup(). That struct ppp is the hdlc->state allocation, which detach_hdlc_protocol() frees with kfree() in both teardown paths: unregister_hdlc_device() and the re-attach inside attach_hdlc_protocol(). The ppp proto never registered a .detach callback, so detach_hdlc_protocol() performs no timer synchronization before the kfree(). The only cancel, timer_delete(&proto->timer) in ppp_cp_event(), is partial (it does not wait for a running callback) and only runs on the ->CLOSED transition; ppp_stop()/ppp_close() do not sync either. A ppp_timer callback already executing (blocked on ppp->lock) survives the kfree and then dereferences proto->state / ppp->lock in freed memory, leading to a use-after-free. Fix this by adding a .detach helper that calls timer_shutdown_sync() on every per-proto timer. detach_hdlc_protocol() invokes proto->detach(dev) before kfree(hdlc->state), so timer_shutdown_sync() now runs on both free paths. timer_shutdown_sync() is used instead of timer_delete_sync() because the keepalive path re-arms the timer through add_timer()/mod_timer() and shutdown blocks any re-activation during teardown. Initialize the per-protocol timers in ppp_ioctl() when the protocol is attached, and remove the now-redundant timer_setup() from ppp_start(), so that the timers are initialized exactly once at attach time and ppp_timer_release() never operates on uninitialized timer_list structures. attach_hdlc_protocol() uses kmalloc() (not kzalloc), so struct ppp's protos[i].timer is uninitialized garbage until the first timer_setup(); without this init-at-attach, attaching the PPP protocol without ever bringing the device up would leave timer_shutdown_sync() operating on uninitialized memory in .detach. Moving the init out of ppp_start() (which only runs on NETDEV_UP) into the attach path makes the initialization unconditional and avoids initializing the same timer_list twice. This bug was found by static analysis. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Fan Wu Link: https://patch.msgid.link/20260617020518.116319-1-fanwu01@zju.edu.cn Signed-off-by: Jakub Kicinski --- drivers/net/wan/hdlc_ppp.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/net/wan/hdlc_ppp.c b/drivers/net/wan/hdlc_ppp.c index 159295c4bd6d8..302ed27944e7c 100644 --- a/drivers/net/wan/hdlc_ppp.c +++ b/drivers/net/wan/hdlc_ppp.c @@ -619,7 +619,6 @@ static void ppp_start(struct net_device *dev) struct proto *proto = &ppp->protos[i]; proto->dev = dev; - timer_setup(&proto->timer, ppp_timer, 0); proto->state = CLOSED; } ppp->protos[IDX_LCP].pid = PID_LCP; @@ -639,6 +638,15 @@ static void ppp_close(struct net_device *dev) ppp_tx_flush(); } +static void ppp_timer_release(struct net_device *dev) +{ + struct ppp *ppp = get_ppp(dev); + int i; + + for (i = 0; i < IDX_COUNT; i++) + timer_shutdown_sync(&ppp->protos[i].timer); +} + static struct hdlc_proto proto = { .start = ppp_start, .stop = ppp_stop, @@ -647,6 +655,7 @@ static struct hdlc_proto proto = { .ioctl = ppp_ioctl, .netif_rx = ppp_rx, .module = THIS_MODULE, + .detach = ppp_timer_release, }; static const struct header_ops ppp_header_ops = { @@ -657,7 +666,7 @@ static int ppp_ioctl(struct net_device *dev, struct if_settings *ifs) { hdlc_device *hdlc = dev_to_hdlc(dev); struct ppp *ppp; - int result; + int i, result; switch (ifs->type) { case IF_GET_PROTO: @@ -685,6 +694,8 @@ static int ppp_ioctl(struct net_device *dev, struct if_settings *ifs) return result; ppp = get_ppp(dev); + for (i = 0; i < IDX_COUNT; i++) + timer_setup(&ppp->protos[i].timer, ppp_timer, 0); spin_lock_init(&ppp->lock); ppp->req_timeout = 2; ppp->cr_retries = 10; -- 2.47.3