[PATCH 6.18 711/752] atm: fore200e: fix use-after-free in tasklets during device removal

Sasha Levin
2026-02-28T17:58:49Z

From: Duoming Zhou <duoming@zju.edu.cn>

[ Upstream commit 8930878101cd40063888a68af73b1b0f8b6c79bc ]

When the PCA-200E or SBA-200E adapter is being detached, the fore200e
is deallocated. However, the tx_tasklet or rx_tasklet may still be running
or pending, leading to use-after-free bug when the already freed fore200e
is accessed again in fore200e_tx_tasklet() or fore200e_rx_tasklet().

One of the race conditions can occur as follows:

CPU 0 (cleanup) | CPU 1 (tasklet)
fore200e_pca_remove_one() | fore200e_interrupt()
fore200e_shutdown() | tasklet_schedule()
kfree(fore200e) | fore200e_tx_tasklet()
| fore200e-> // UAF

Fix this by ensuring tx_tasklet or rx_tasklet is properly canceled before
the fore200e is released. Add tasklet_kill() in fore200e_shutdown() to
synchronize with any pending or running tasklets. Moreover, since
fore200e_reset() could prevent further interrupts or data transfers,
the tasklet_kill() should be placed after fore200e_reset() to prevent
the tasklet from being rescheduled in fore200e_interrupt(). Finally,
it only needs to do tasklet_kill() when the fore200e state is greater
than or equal to FORE200E_STATE_IRQ, since tasklets are uninitialized
in earlier states. In a word, the tasklet_kill() should be placed in
the FORE200E_STATE_IRQ branch within the switch...case structure.

This bug was identified through static analysis.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@kernel.org
Suggested-by: Jijie Shao <shaojijie@huawei.com>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Jijie Shao <shaojijie@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260210094537.9767-1-duoming@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/atm/fore200e.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/atm/fore200e.c b/drivers/atm/fore200e.c
index f62e385714403..fec081db36dc4 100644
--- a/drivers/atm/fore200e.c
+++ b/drivers/atm/fore200e.c
@@ -373,6 +373,10 @@ fore200e_shutdown(struct fore200e* fore200e)
fallthrough;
case FORE200E_STATE_IRQ:
free_irq(fore200e->irq, fore200e->atm_dev);
+#ifdef FORE200E_USE_TASKLET
+ tasklet_kill(&fore200e->tx_tasklet);
+ tasklet_kill(&fore200e->rx_tasklet);
+#endif

fallthrough;
case FORE200E_STATE_ALLOC_BUF:
--
2.51.0