Re: [PATCH] ata: pata_parport: Fix use-after-free in new_device_store

[Pei Xiao]

在 2026/7/30 07:42, Damien Le Moal 写道:
> On 7/29/26 21:27, Pei Xiao wrote:
>> The function new_device_store() calls driver_find() without any
>> protection against concurrent driver unregistration. This can lead
>> to a use-after-free (UAF) when a driver is unloaded (via rmmod)
>> in parallel with a new device addition via sysfs.
>>
>> The race window exists because driver_find() returns a pointer to
>> the driver's private data, but does not increase its reference
>> count. The caller is responsible for ensuring the driver remains
>> valid, but new_device_store() did not hold any lock or reference
>> during the lookup and subsequent use.
>>
>> Concurrently, pata_parport_unregister_driver() releases the
>> pi_mutex before calling driver_unregister(), allowing new_device_store
>> to proceed with a stale pointer after the driver has been freed.
>>
>> Fix this by expanding the critical section protected by pi_mutex
>> in both functions:
>>
>> - In new_device_store(): acquire pi_mutex before calling driver_find(),
>>   and keep it held until all uses of the found driver pointer are
>>   completed.
>> - In pata_parport_unregister_driver(): hold pi_mutex throughout the
>>   entire unregistration process, including the driver_unregister()
>>   call, so that no concurrent lookup can see a partially removed
>>   driver.
>>
>> Thread A (new_device_store)       | Thread B (pata_parport_unregister_driver)
>>   driver_find("aten")             |
>>                                   |   mutex_lock(&pi_mutex)
>>                                   |   idr_remove(&protocols, id)
>>                                   |   mutex_unlock(&pi_mutex)
>>                                   |   driver_unregister(&pr->driver)
>>                                   |   (frees driver_private)
>>   /* continues using stale driv */|
>>   -> UAF!                         |
>>
>> Logs:
>> BUG: KASAN: slab-use-after-free in driver_find+0xd0/0xd4
>> Read of size 8 at addr ffffff9f970dc690 by task sh/4737
>> Call trace:
>>  show_stack+0x14/0x1c (C)
>>  dump_stack_lvl+0x70/0x84
>>  print_report+0xf4/0x5a4
>>  kasan_report+0xa0/0xe4
>>  __asan_report_load8_noabort+0x18/0x20
>>  driver_find+0xd0/0xd4
>>  new_device_store+0x140/0x30c [pata_parport]
>>  bus_attr_store+0x5c/0x94
>>  sysfs_kf_write+0x1c4/0x25c
>>  ...
>>
>> Allocated by task 4734:
>>  kasan_save_stack+0x28/0x4c
>>  kasan_save_track+0x1c/0x34
>>  kasan_save_alloc_info+0x3c/0x4c
>>  __kasan_kmalloc+0x98/0xac
>>  __kmalloc_cache_noprof+0x158/0x3cc
>>  bus_add_driver+0x70/0x4d8
>>  driver_register+0xf0/0x3b0
>>  pata_parport_register_driver+0xb8/0x1c4 [pata_parport]
>>  0xffffffc07f5ce014
>>  do_one_initcall+0xb8/0x36c
>>  do_init_module+0x230/0x6d4
>>  ...
>>
>> Freed by task 4737:
>>  kasan_save_stack+0x28/0x4c
>>  kasan_save_track+0x1c/0x34
>>  kasan_save_free_info+0x48/0x8c
>>  __kasan_slab_free+0x5c/0x84
>>  kfree+0x174/0x3e0
>>  driver_release+0x1c/0x7c
>>  kobject_put+0x178/0x47c
>>  driver_find+0x78/0xd4
>>  new_device_store+0x140/0x30c [pata_parport]
>>  bus_attr_store+0x5c/0x94
>>  sysfs_kf_write+0x1c4/0x25c
>>  ...
>>
>> Fixes: 72f2b0b21850 ("drivers/block: Move PARIDE protocol modules to drivers/ata/pata_parport")
>> Reported-by: Shuangpeng Bai <shuangpeng.kernel@xxxxxxxxx>
>> Closes: https://lore.kernel.org/lkml/20260728024015.2014674-1-shuangpeng.kernel@xxxxxxxxx/
>> Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
>> ---
>>  drivers/ata/pata_parport/pata_parport.c | 9 ++++-----
>>  1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/ata/pata_parport/pata_parport.c b/drivers/ata/pata_parport/pata_parport.c
>> index 40baeac594a9..34f09192a419 100644
>> --- a/drivers/ata/pata_parport/pata_parport.c
>> +++ b/drivers/ata/pata_parport/pata_parport.c
>> @@ -3,6 +3,7 @@
>>   * Copyright 2023 Ondrej Zary
>>   * based on paride.c by Grant R. Guenther <grant@xxxxxxxxxx>
>>   */
>> +#include <linux/cleanup.h>
>>  #include <linux/kernel.h>
>>  #include <linux/module.h>
>>  #include <linux/parport.h>
>> @@ -618,8 +619,9 @@ void pata_parport_unregister_driver(struct pi_protocol *pr)
>>  			break;
>>  	}
>>  	idr_remove(&protocols, id);
>> -	mutex_unlock(&pi_mutex);
>>  	driver_unregister(&pr->driver);
>> +	mutex_unlock(&pi_mutex);
> 
> Sashiko had a comment about this that I think is very valid: if rmmod is
> executed with devices attached, what happens here?
> This entire driver seems to be lacking reference counting on the
> modules/drivers, so this all seems very fragile.
Ok, I will check this issue then.
> 
>> +
>>  }
>>  EXPORT_SYMBOL_GPL(pata_parport_unregister_driver);
>>  
>> @@ -646,6 +648,7 @@ static ssize_t new_device_store(const struct bus_type *bus, const char *buf, siz
>>  		port_wanted = -1;
>>  	}
>>  
>> +	guard(mutex)(&pi_mutex);
> 
> Please no. We do not use these annotations anywhere in libata and I personally
> consider anything that hides code a *bad* idea. So just move the mutex_lock()
> call here and add the missing mutex_unlock() in the !drv case below.
Ok.

Thanks!
Pei.
> 
>>  	drv = driver_find(protocol, &pata_parport_bus_type);
>>  	if (!drv) {
>>  		if (strcmp(protocol, "auto")) {
>> @@ -656,15 +659,12 @@ static ssize_t new_device_store(const struct bus_type *bus, const char *buf, siz
>>  	} else {
>>  		pr_wanted = container_of(drv, struct pi_protocol, driver);
>>  	}
>> -
>> -	mutex_lock(&pi_mutex);
>>  	/* walk all parports */
>>  	idr_for_each_entry(&parport_list, parport, port_num) {
>>  		if (port_num == port_wanted || port_wanted == -1) {
>>  			parport = parport_find_number(port_num);
>>  			if (!parport) {
>>  				pr_err("no such port %s\n", port);
>> -				mutex_unlock(&pi_mutex);
>>  				return -ENODEV;
>>  			}
>>  			/* walk all protocols */
>> @@ -677,7 +677,6 @@ static ssize_t new_device_store(const struct bus_type *bus, const char *buf, siz
>>  			parport_put_port(parport);
>>  		}
>>  	}
>> -	mutex_unlock(&pi_mutex);
>>  	if (!ok)
>>  		return -ENODEV;
>>  
> 
>