2023-09-25 07:52:17

by Wang Jinchao

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

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 <[email protected]>
---
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


2023-09-27 07:39:31

by kernel test robot

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

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/[email protected]/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/[email protected]/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 <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

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