Messages in this thread Patch in this message | | | Date | Thu, 28 Sep 2023 08:38:53 +0800 | From | Wang Jinchao <> | Subject | [PATCH v2] padata: Fix the UAF issue related to parallel_data |
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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->serial = serial; 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> --- V2: To satisfy Sparse, use rcu_dereference_protected. Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202309270829.xHgTOMKw-lkp@intel.com/
V1: https://lore.kernel.org/all/ZRE4XvOOhz4HSOgR@fedora/
kernel/padata.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/padata.c b/kernel/padata.c index 222d60195de6..acef1e703a8b 100644 --- a/kernel/padata.c +++ b/kernel/padata.c @@ -1107,7 +1107,9 @@ 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)); + struct parallel_data *pd = rcu_dereference_protected(ps->pd, 1); + if (refcount_dec_and_test(&pd->refcnt)) + padata_free_pd(pd); mutex_unlock(&ps->pinst->lock); kfree(ps); -- 2.40.0
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