* [PATCH net v4 1/2] s390/ctcm: Fix timer corruption in fsm_addtimer()
[not found] <20260930070234.569500-1-nagamani@linux.ibm.com>
@ 2026-09-30 7:02 ` Nagamani PV
2026-10-05 17:16 ` Simon Horman
2026-09-30 7:02 ` [PATCH net v4 2/2] s390/ctcm: Fix use-after-free in channel_remove() Nagamani PV
1 sibling, 1 reply; 4+ messages in thread
From: Nagamani PV @ 2026-09-30 7:02 UTC (permalink / raw)
To: andrew+netdev, davem, edumazet, kuba, pabeni
Cc: wintera, aswin, hca, gor, agordeev, borntraeger, svens, kees,
linux-s390, netdev, Nagamani PV, stable, Sashiko
fsm_addtimer() calls timer_setup() unconditionally before add_timer().
If called on an already-pending timer, timer_setup() re-initializes
the timer's list_head fields while the timer is still enqueued in the
wheel, corrupting the timer list.
The timer is already initialized once by fsm_settimer() which calls
timer_setup() correctly. Multiple callsites invoke fsm_addtimer()
without a preceding fsm_deltimer(), including ctcm_main.c
ctcmpc_send_sweep_req() and ctcm_mpc.c mpc_action_side_xid(), making the
redundant timer_setup() in fsm_addtimer() a real corruption risk.
Remove the redundant timer_setup() calls from fsm_addtimer() and
fsm_modtimer(), and replace add_timer() with mod_timer() which safely
handles both pending and non-pending timers atomically without
corrupting the timer wheel.
Fixes: e99e88a9d2b0 ("treewide: setup_timer() -> timer_setup()")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260803182736.2356374-1-nagamani@linux.ibm.com?part=1
Reviewed-by: Aswin Karuvally <aswin@linux.ibm.com>
Tested-by: Aswin Karuvally <aswin@linux.ibm.com>
Signed-off-by: Nagamani PV <nagamani@linux.ibm.com>
---
Changes in v4:
- No changes to this patch.
Changes in v3:
- No changes to this patch.
Changes in v2:
- Fix function name ctcm_send_sweep() -> ctcmpc_send_sweep_req()
in the commit message.
- Call mod_timer() then return 0 explicitly, preserving the
"Always returns 0" contract documented in fsm.h.
---
drivers/s390/net/fsm.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/drivers/s390/net/fsm.c b/drivers/s390/net/fsm.c
index 9b8622aef807..936ed0bc8401 100644
--- a/drivers/s390/net/fsm.c
+++ b/drivers/s390/net/fsm.c
@@ -171,11 +171,9 @@ fsm_addtimer(fsm_timer *this, int millisec, int event, void *arg)
this->fi->name, this, millisec);
#endif
- timer_setup(&this->tl, fsm_expire_timer, 0);
this->expire_event = event;
this->event_arg = arg;
- this->tl.expires = jiffies + (millisec * HZ) / 1000;
- add_timer(&this->tl);
+ mod_timer(&this->tl, jiffies + msecs_to_jiffies(millisec));
return 0;
}
@@ -189,12 +187,9 @@ fsm_modtimer(fsm_timer *this, int millisec, int event, void *arg)
this->fi->name, this, millisec);
#endif
- timer_delete(&this->tl);
- timer_setup(&this->tl, fsm_expire_timer, 0);
this->expire_event = event;
this->event_arg = arg;
- this->tl.expires = jiffies + (millisec * HZ) / 1000;
- add_timer(&this->tl);
+ mod_timer(&this->tl, jiffies + msecs_to_jiffies(millisec));
}
EXPORT_SYMBOL(init_fsm);
--
2.53.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH net v4 2/2] s390/ctcm: Fix use-after-free in channel_remove()
[not found] <20260930070234.569500-1-nagamani@linux.ibm.com>
2026-09-30 7:02 ` [PATCH net v4 1/2] s390/ctcm: Fix timer corruption in fsm_addtimer() Nagamani PV
@ 2026-09-30 7:02 ` Nagamani PV
2026-10-05 17:16 ` Simon Horman
1 sibling, 1 reply; 4+ messages in thread
From: Nagamani PV @ 2026-09-30 7:02 UTC (permalink / raw)
To: andrew+netdev, davem, edumazet, kuba, pabeni
Cc: wintera, aswin, hca, gor, agordeev, borntraeger, svens, kees,
linux-s390, netdev, Nagamani PV, stable, Sashiko
channel_remove() uses fsm_deltimer() which calls timer_delete(),
returning immediately even if the timer callback is running on
another CPU. This leaves a window where fsm_expire_timer() accesses
ch->fsm after kfree_fsm().
For MPC channels the teardown has a circular dependency:
ch->timer callback -> ctcm_chx_txretry() -> mpc_action_go_inop()
-> tasklet_hi_schedule(&ch->ch_disc_tasklet)
ch_tasklet -> ctcmpc_send_sweep_resp() -> fsm_addtimer(&ch->sweep_timer)
sweep_timer callback -> fsm_addtimer(&ch->timer)
Use timer_shutdown_sync() for both timers: it waits for any running
callback and permanently prevents rearming. Shut down sweep_timer
first (its callback rearms ch->timer at ctcm_fsms.c), then
ch->timer. Only then call tasklet_kill() -- catching any tasklet
scheduled by an in-flight callback before shutdown.
kfree(ch->discontact_th) follows tasklet_kill(ch_disc_tasklet) since
ch->ccw[15].cda points to discontact_th and
mpc_action_send_discontact() starts I/O through ch->ccw[15].
timer_shutdown_sync() is also used for non-MPC ch->timer:
ctcm_chx_txretry() (CTC_STATE_TX + CTC_EVENT_TIMER) calls
fsm_addtimer(&ch->timer) on both paths.
Depends on "s390/ctcm: Fix timer corruption in fsm_addtimer()" which
replaces add_timer() with mod_timer(). mod_timer() on a shut-down
timer is discarded; without it fsm_addtimer() calls timer_setup()
defeating timer_shutdown_sync(). Backporting without that
prerequisite is unsafe.
Fixes: 293d984f0e36 ("ctcm: infrastructure for replaced ctc driver")
Cc: stable@vger.kernel.org # depends on: s390/ctcm: Fix timer corruption in fsm_addtimer()
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260922101913.239103-1-nagamani@linux.ibm.com?part=2
Signed-off-by: Nagamani PV <nagamani@linux.ibm.com>
---
Changes in v4:
- Shut down timers before tasklet_kill() rather than after,
shutting down sweep_timer before ch->timer.
- Use timer_shutdown_sync() for ch->timer on both MPC and non-MPC paths.
- Name prerequisite by commit title and add structured stable tag
dependency (Jakub Kicinski).
- Code changed; Reviewed-by and Tested-by dropped.
Changes in v3:
- Kill ch_tasklet and ch_disc_tasklet before stopping the timers and
freeing ch->fsm: closes freed ch->fsm access from tasklet context and
eliminates tasklet-driven sweep_timer re-arm.
- Shut down sweep_timer with timer_shutdown_sync() before deleting
ch->timer to prevent sweep_timer callback from re-arming ch->timer.
- Move kfree(ch->discontact_th) after tasklet_kill(ch_disc_tasklet).
- Drop Reviewed-by and Tested-by; please re-review and re-test the
new teardown order.
Changes in v2:
- Add Fixes: and Cc: stable@vger.kernel.org tags.
---
drivers/s390/net/ctcm_main.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/drivers/s390/net/ctcm_main.c b/drivers/s390/net/ctcm_main.c
index 8b0d76a47d9f..27a22dbc9280 100644
--- a/drivers/s390/net/ctcm_main.c
+++ b/drivers/s390/net/ctcm_main.c
@@ -211,9 +211,14 @@ static void channel_remove(struct channel *ch)
while (*c) {
if (*c == ch) {
*c = ch->next;
- fsm_deltimer(&ch->timer);
if (IS_MPC(ch))
- fsm_deltimer(&ch->sweep_timer);
+ timer_shutdown_sync(&ch->sweep_timer.tl);
+ timer_shutdown_sync(&ch->timer.tl);
+ if (IS_MPC(ch)) {
+ tasklet_kill(&ch->ch_tasklet);
+ tasklet_kill(&ch->ch_disc_tasklet);
+ kfree(ch->discontact_th);
+ }
kfree_fsm(ch->fsm);
clear_normalized_cda(&ch->ccw[4]);
@@ -221,11 +226,6 @@ static void channel_remove(struct channel *ch)
clear_normalized_cda(&ch->ccw[1]);
dev_kfree_skb_any(ch->trans_skb);
}
- if (IS_MPC(ch)) {
- tasklet_kill(&ch->ch_tasklet);
- tasklet_kill(&ch->ch_disc_tasklet);
- kfree(ch->discontact_th);
- }
kfree(ch->ccw);
kfree(ch->irb);
kfree(ch);
--
2.53.0
^ permalink raw reply related [flat|nested] 4+ messages in thread