[PATCH] padata: Fix the UAF issue related to parallel_data

[PATCH] padata: Fix the UAF issue related to parallel_data

[Wang Jinchao]

In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead to
system UAF (Use-After-Free) issues. Due to the lengthy analysis of the
pcrypt_aead01 function call, I'll describe the problem scenario using a
simplified model:

Suppose there's a user of padata named `user_function` that adheres to
the padata requirement of calling `padata_free_shell` after `serial()`
has been invoked, as demonstrated in the following code:

```c
struct request {
    struct padata_priv padata;
    struct completion *done;
};

void parallel(struct padata_priv *padata) {
    do_something();
}

void serial(struct padata_priv *padata) {
    struct request *request = container_of(padata, struct request, padata);
    complete(request->done);
}

void user_function() {
    DECLARE_COMPLETION(done)
    padata->parallel = parallel()
    padata_do_parallel();
    wait_for_completion(&done);
    padata_free_shell();
}
```

In the corresponding padata.c file, there's the following code:

```c
static void padata_serial_worker(struct work_struct *serial_work) {
    ...
    cnt = 0;

    while (!list_empty(&local_list)) {
        ...
        padata->serial(padata);
        cnt++;
    }

    local_bh_enable();

    if (refcount_sub_and_test(cnt, &pd->refcnt))
        padata_free_pd(pd);
}
```

Because of the high system load and the accumulation of unexecuted
softirq at this moment, `local_bh_enable()` in padata takes longer
to execute than usual. Subsequently, when accessing `pd->refcnt`,
`pd` has already been released by `padata_free_shell()`, resulting
in a UAF issue with `pd->refcnt`.

The fix is straightforward: add `refcount_dec_and_test` before calling
`padata_free_pd` in `padata_free_shell`.

Signed-off-by: Wang Jinchao <wangjinchao@xfusion.com>
---
 kernel/padata.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 222d60195de6..15dbcf7ce623 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -1107,7 +1107,8 @@ void padata_free_shell(struct padata_shell *ps)
 
 	mutex_lock(&ps->pinst->lock);
 	list_del(&ps->list);
-	padata_free_pd(rcu_dereference_protected(ps->pd, 1));
+	if (refcount_dec_and_test(&ps->pd->refcnt))
+		padata_free_pd(rcu_dereference_protected(ps->pd, 1));
 	mutex_unlock(&ps->pinst->lock);
 
 	kfree(ps);
-- 
2.40.0

Re: [PATCH] padata: Fix the UAF issue related to parallel_data

[kernel test robot]

Hi Wang,

kernel test robot noticed the following build warnings:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.6-rc3 next-20230926]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Wang-Jinchao/padata-Fix-the-UAF-issue-related-to-parallel_data/20230925-153852
base:   linus/master
patch link:    https://lore.kernel.org/r/ZRE4XvOOhz4HSOgR%40fedora
patch subject: [PATCH] padata: Fix the UAF issue related to parallel_data
config: i386-randconfig-062-20230925 (https://download.01.org/0day-ci/archive/20230927/202309270829.xHgTOMKw-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-12) 11.3.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230927/202309270829.xHgTOMKw-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309270829.xHgTOMKw-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> kernel/padata.c:1110:38: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct refcount_struct [usertype] *r @@     got struct refcount_struct [noderef] __rcu * @@
   kernel/padata.c:1110:38: sparse:     expected struct refcount_struct [usertype] *r
   kernel/padata.c:1110:38: sparse:     got struct refcount_struct [noderef] __rcu *

vim +1110 kernel/padata.c

  1097	
  1098	/**
  1099	 * padata_free_shell - free a padata shell
  1100	 *
  1101	 * @ps: padata shell to free
  1102	 */
  1103	void padata_free_shell(struct padata_shell *ps)
  1104	{
  1105		if (!ps)
  1106			return;
  1107	
  1108		mutex_lock(&ps->pinst->lock);
  1109		list_del(&ps->list);
> 1110		if (refcount_dec_and_test(&ps->pd->refcnt))
  1111			padata_free_pd(rcu_dereference_protected(ps->pd, 1));
  1112		mutex_unlock(&ps->pinst->lock);
  1113	
  1114		kfree(ps);
  1115	}
  1116	EXPORT_SYMBOL(padata_free_shell);
  1117	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki