[PATCH net] net: wan: farsync: Fix use-after-free bugs caused by unfinished tasklets

[PATCH net] net: wan: farsync: Fix use-after-free bugs caused by unfinished tasklets

[Duoming Zhou]

When the FarSync T-series card is being detached, the fst_card_info is
deallocated in fst_remove_one(). However, the fst_tx_task or fst_int_task
may still be running or pending, leading to use-after-free bugs when the
already freed fst_card_info is accessed in fst_process_tx_work_q() or
fst_process_int_work_q().

A typical race condition is depicted below:

CPU 0 (cleanup)           | CPU 1 (tasklet)
                          | fst_start_xmit()
fst_remove_one()          |   tasklet_schedule()
  unregister_hdlc_device()|
                          | fst_process_tx_work_q() //handler
  kfree(card) //free      |   do_bottom_half_tx()
                          |     card-> //use

The following KASAN trace was captured:

==================================================================
 BUG: KASAN: slab-use-after-free in do_bottom_half_tx+0xb88/0xd00
 Read of size 4 at addr ffff88800aad101c by task ksoftirqd/3/32
 ...
 Call Trace:
  <IRQ>
  dump_stack_lvl+0x55/0x70
  print_report+0xcb/0x5d0
  ? do_bottom_half_tx+0xb88/0xd00
  kasan_report+0xb8/0xf0
  ? do_bottom_half_tx+0xb88/0xd00
  do_bottom_half_tx+0xb88/0xd00
  ? _raw_spin_lock_irqsave+0x85/0xe0
  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
  ? __pfx___hrtimer_run_queues+0x10/0x10
  fst_process_tx_work_q+0x67/0x90
  tasklet_action_common+0x1fa/0x720
  ? hrtimer_interrupt+0x31f/0x780
  handle_softirqs+0x176/0x530
  __irq_exit_rcu+0xab/0xe0
  sysvec_apic_timer_interrupt+0x70/0x80
 ...

 Allocated by task 41 on cpu 3 at 72.330843s:
  kasan_save_stack+0x24/0x50
  kasan_save_track+0x17/0x60
  __kasan_kmalloc+0x7f/0x90
  fst_add_one+0x1a5/0x1cd0
  local_pci_probe+0xdd/0x190
  pci_device_probe+0x341/0x480
  really_probe+0x1c6/0x6a0
  __driver_probe_device+0x248/0x310
  driver_probe_device+0x48/0x210
  __device_attach_driver+0x160/0x320
  bus_for_each_drv+0x101/0x190
  __device_attach+0x198/0x3a0
  device_initial_probe+0x78/0xa0
  pci_bus_add_device+0x81/0xc0
  pci_bus_add_devices+0x7e/0x190
  enable_slot+0x9b9/0x1130
  acpiphp_check_bridge.part.0+0x2e1/0x460
  acpiphp_hotplug_notify+0x36c/0x3c0
  acpi_device_hotplug+0x203/0xb10
  acpi_hotplug_work_fn+0x59/0x80
 ...

 Freed by task 41 on cpu 1 at 75.138639s:
  kasan_save_stack+0x24/0x50
  kasan_save_track+0x17/0x60
  kasan_save_free_info+0x3b/0x60
  __kasan_slab_free+0x43/0x70
  kfree+0x135/0x410
  fst_remove_one+0x2ca/0x540
  pci_device_remove+0xa6/0x1d0
  device_release_driver_internal+0x364/0x530
  pci_stop_bus_device+0x105/0x150
  pci_stop_and_remove_bus_device+0xd/0x20
  disable_slot+0x116/0x260
  acpiphp_disable_and_eject_slot+0x4b/0x190
  acpiphp_hotplug_notify+0x230/0x3c0
  acpi_device_hotplug+0x203/0xb10
  acpi_hotplug_work_fn+0x59/0x80
 ...

 The buggy address belongs to the object at ffff88800aad1000
  which belongs to the cache kmalloc-1k of size 1024
 The buggy address is located 28 bytes inside of
  freed 1024-byte region
 The buggy address belongs to the physical page:
 page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xaad0
 head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
 flags: 0x100000000000040(head|node=0|zone=1)
 page_type: f5(slab)
 raw: 0100000000000040 ffff888007042dc0 dead000000000122 0000000000000000
 raw: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
 head: 0100000000000040 ffff888007042dc0 dead000000000122 0000000000000000
 head: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
 head: 0100000000000003 ffffea00002ab401 00000000ffffffff 00000000ffffffff
 head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffff88800aad0f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff88800aad0f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 >ffff88800aad1000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                             ^
  ffff88800aad1080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff88800aad1100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ==================================================================

Fix this by ensuring that both fst_tx_task and fst_int_task are properly
canceled before the fst_card_info is released. Add tasklet_kill() in
fst_remove_one() to synchronize with any pending or running tasklets.
Since unregister_hdlc_device() stops data transmission and reception,
and fst_disable_intr() prevents further interrupts, it is appropriate
to place tasklet_kill() after these calls.

The bugs were identified through static analysis. To reproduce the issue
and validate the fix, a FarSync T-series card was simulated in QEMU and
delays(e.g., mdelay()) were introduced within the tasklet handler to
increase the likelihood of triggering the race condition.

Fixes: 2f623aaf9f31 ("net: farsync: Fix kmemleak when rmmods farsync")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
 drivers/net/wan/farsync.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/wan/farsync.c b/drivers/net/wan/farsync.c
index 5b01642ca44..6b2d1e63855 100644
--- a/drivers/net/wan/farsync.c
+++ b/drivers/net/wan/farsync.c
@@ -2550,6 +2550,8 @@ fst_remove_one(struct pci_dev *pdev)
 
 	fst_disable_intr(card);
 	free_irq(card->irq, card);
+	tasklet_kill(&fst_tx_task);
+	tasklet_kill(&fst_int_task);
 
 	iounmap(card->ctlmem);
 	iounmap(card->mem);
-- 
2.34.1

Re: [PATCH net] net: wan: farsync: Fix use-after-free bugs caused by unfinished tasklets

[Jijie Shao]

on 2026/2/19 20:46, Duoming Zhou wrote:
> When the FarSync T-series card is being detached, the fst_card_info is
> deallocated in fst_remove_one(). However, the fst_tx_task or fst_int_task
> may still be running or pending, leading to use-after-free bugs when the
> already freed fst_card_info is accessed in fst_process_tx_work_q() or
> fst_process_int_work_q().
>
> A typical race condition is depicted below:
>
> CPU 0 (cleanup)           | CPU 1 (tasklet)
>                            | fst_start_xmit()
> fst_remove_one()          |   tasklet_schedule()
>    unregister_hdlc_device()|
>                            | fst_process_tx_work_q() //handler
>    kfree(card) //free      |   do_bottom_half_tx()
>                            |     card-> //use
>
> The following KASAN trace was captured:
>
> ==================================================================
>   BUG: KASAN: slab-use-after-free in do_bottom_half_tx+0xb88/0xd00
>   Read of size 4 at addr ffff88800aad101c by task ksoftirqd/3/32
>   ...
>   Call Trace:
>    <IRQ>
>    dump_stack_lvl+0x55/0x70
>    print_report+0xcb/0x5d0
>    ? do_bottom_half_tx+0xb88/0xd00
>    kasan_report+0xb8/0xf0
>    ? do_bottom_half_tx+0xb88/0xd00
>    do_bottom_half_tx+0xb88/0xd00
>    ? _raw_spin_lock_irqsave+0x85/0xe0
>    ? __pfx__raw_spin_lock_irqsave+0x10/0x10
>    ? __pfx___hrtimer_run_queues+0x10/0x10
>    fst_process_tx_work_q+0x67/0x90
>    tasklet_action_common+0x1fa/0x720
>    ? hrtimer_interrupt+0x31f/0x780
>    handle_softirqs+0x176/0x530
>    __irq_exit_rcu+0xab/0xe0
>    sysvec_apic_timer_interrupt+0x70/0x80
>   ...
>
>   Allocated by task 41 on cpu 3 at 72.330843s:
>    kasan_save_stack+0x24/0x50
>    kasan_save_track+0x17/0x60
>    __kasan_kmalloc+0x7f/0x90
>    fst_add_one+0x1a5/0x1cd0
>    local_pci_probe+0xdd/0x190
>    pci_device_probe+0x341/0x480
>    really_probe+0x1c6/0x6a0
>    __driver_probe_device+0x248/0x310
>    driver_probe_device+0x48/0x210
>    __device_attach_driver+0x160/0x320
>    bus_for_each_drv+0x101/0x190
>    __device_attach+0x198/0x3a0
>    device_initial_probe+0x78/0xa0
>    pci_bus_add_device+0x81/0xc0
>    pci_bus_add_devices+0x7e/0x190
>    enable_slot+0x9b9/0x1130
>    acpiphp_check_bridge.part.0+0x2e1/0x460
>    acpiphp_hotplug_notify+0x36c/0x3c0
>    acpi_device_hotplug+0x203/0xb10
>    acpi_hotplug_work_fn+0x59/0x80
>   ...
>
>   Freed by task 41 on cpu 1 at 75.138639s:
>    kasan_save_stack+0x24/0x50
>    kasan_save_track+0x17/0x60
>    kasan_save_free_info+0x3b/0x60
>    __kasan_slab_free+0x43/0x70
>    kfree+0x135/0x410
>    fst_remove_one+0x2ca/0x540
>    pci_device_remove+0xa6/0x1d0
>    device_release_driver_internal+0x364/0x530
>    pci_stop_bus_device+0x105/0x150
>    pci_stop_and_remove_bus_device+0xd/0x20
>    disable_slot+0x116/0x260
>    acpiphp_disable_and_eject_slot+0x4b/0x190
>    acpiphp_hotplug_notify+0x230/0x3c0
>    acpi_device_hotplug+0x203/0xb10
>    acpi_hotplug_work_fn+0x59/0x80
>   ...
>
>   The buggy address belongs to the object at ffff88800aad1000
>    which belongs to the cache kmalloc-1k of size 1024
>   The buggy address is located 28 bytes inside of
>    freed 1024-byte region
>   The buggy address belongs to the physical page:
>   page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xaad0
>   head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
>   flags: 0x100000000000040(head|node=0|zone=1)
>   page_type: f5(slab)
>   raw: 0100000000000040 ffff888007042dc0 dead000000000122 0000000000000000
>   raw: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
>   head: 0100000000000040 ffff888007042dc0 dead000000000122 0000000000000000
>   head: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
>   head: 0100000000000003 ffffea00002ab401 00000000ffffffff 00000000ffffffff
>   head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
>   page dumped because: kasan: bad access detected
>
>   Memory state around the buggy address:
>    ffff88800aad0f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>    ffff88800aad0f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   >ffff88800aad1000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                               ^
>    ffff88800aad1080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>    ffff88800aad1100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ==================================================================
>
> Fix this by ensuring that both fst_tx_task and fst_int_task are properly
> canceled before the fst_card_info is released. Add tasklet_kill() in
> fst_remove_one() to synchronize with any pending or running tasklets.
> Since unregister_hdlc_device() stops data transmission and reception,
> and fst_disable_intr() prevents further interrupts, it is appropriate
> to place tasklet_kill() after these calls.
>
> The bugs were identified through static analysis. To reproduce the issue
> and validate the fix, a FarSync T-series card was simulated in QEMU and
> delays(e.g., mdelay()) were introduced within the tasklet handler to
> increase the likelihood of triggering the race condition.
>
> Fixes: 2f623aaf9f31 ("net: farsync: Fix kmemleak when rmmods farsync")
> Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>

Reviewed-by: Jijie Shao <shaojijie@huawei.com>

> ---
>   drivers/net/wan/farsync.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/wan/farsync.c b/drivers/net/wan/farsync.c
> index 5b01642ca44..6b2d1e63855 100644
> --- a/drivers/net/wan/farsync.c
> +++ b/drivers/net/wan/farsync.c
> @@ -2550,6 +2550,8 @@ fst_remove_one(struct pci_dev *pdev)
>   
>   	fst_disable_intr(card);
>   	free_irq(card->irq, card);
> +	tasklet_kill(&fst_tx_task);
> +	tasklet_kill(&fst_int_task);
>   
>   	iounmap(card->ctlmem);
>   	iounmap(card->mem);

Re: [PATCH net] net: wan: farsync: Fix use-after-free bugs caused by unfinished tasklets

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Thu, 19 Feb 2026 20:46:37 +0800 you wrote:
> When the FarSync T-series card is being detached, the fst_card_info is
> deallocated in fst_remove_one(). However, the fst_tx_task or fst_int_task
> may still be running or pending, leading to use-after-free bugs when the
> already freed fst_card_info is accessed in fst_process_tx_work_q() or
> fst_process_int_work_q().
> 
> A typical race condition is depicted below:
> 
> [...]

Here is the summary with links:
  - [net] net: wan: farsync: Fix use-after-free bugs caused by unfinished tasklets
    https://git.kernel.org/netdev/net/c/bae8a5d2e759

You are awesome, thank you!
-- 
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