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() {
struct request request;
DECLARE_COMPLETION(done)
request->done = done;
padata = &request.padata;
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 <[email protected]>
Acked-by: Daniel Jordan <[email protected]>
---
V3:
Include Daniel's ack
V2: https://lore.kernel.org/all/ZRTLHY5A+VqIKhA2@fedora/
To satisfy Sparse, use rcu_dereference_protected.
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
V1: https://lore.kernel.org/all/ZRE4XvOOhz4HSOgR@fedora/
kernel/padata.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/padata.c b/kernel/padata.c
index 222d60195de6..79d04a97ded6 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -1102,12 +1102,16 @@ EXPORT_SYMBOL(padata_alloc_shell);
*/
void padata_free_shell(struct padata_shell *ps)
{
+ struct parallel_data *pd;
+
if (!ps)
return;
mutex_lock(&ps->pinst->lock);
list_del(&ps->list);
- padata_free_pd(rcu_dereference_protected(ps->pd, 1));
+ pd = rcu_dereference_protected(ps->pd, 1);
+ if (refcount_dec_and_test(&pd->refcnt))
+ padata_free_pd(rcu_dereference_protected(ps->pd, 1));
mutex_unlock(&ps->pinst->lock);
kfree(ps);
--
2.40.0
Wang Jinchao <[email protected]> wrote:
>
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 222d60195de6..79d04a97ded6 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -1102,12 +1102,16 @@ EXPORT_SYMBOL(padata_alloc_shell);
> */
> void padata_free_shell(struct padata_shell *ps)
> {
> + struct parallel_data *pd;
> +
> if (!ps)
> return;
>
> mutex_lock(&ps->pinst->lock);
> list_del(&ps->list);
> - padata_free_pd(rcu_dereference_protected(ps->pd, 1));
> + pd = rcu_dereference_protected(ps->pd, 1);
> + if (refcount_dec_and_test(&pd->refcnt))
> + padata_free_pd(rcu_dereference_protected(ps->pd, 1));
Why is this dereferencing ps->pd again after the refcount_dec_and_test?
If this is necessary please explain it in the code because it is not
at all obvious.
Thanks,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
Hi,
On Sat, Oct 07, 2023 at 11:52:33AM +0800, Wang Jinchao wrote:
> Signed-off-by: Wang Jinchao <[email protected]>
The Fixes: tag should be near your Signed-off-by:, and the subject of
the patch should be something descriptive like
padata: Fix refcnt handling in padata_free_shell()
Here's some documentation about this:
https://docs.kernel.org/process/5.Posting.html#patch-formatting-and-changelogs
> Acked-by: Daniel Jordan <[email protected]>
> ---
> V3:
> Include Daniel's ack
>
> V2: https://lore.kernel.org/all/ZRTLHY5A+VqIKhA2@fedora/
> To satisfy Sparse, use rcu_dereference_protected.
> Reported-by: kernel test robot <[email protected]>
> Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
These two tags can also go near your SoB.
> V1: https://lore.kernel.org/all/ZRE4XvOOhz4HSOgR@fedora/
>
> kernel/padata.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 222d60195de6..79d04a97ded6 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -1102,12 +1102,16 @@ EXPORT_SYMBOL(padata_alloc_shell);
> */
> void padata_free_shell(struct padata_shell *ps)
> {
> + struct parallel_data *pd;
> +
> if (!ps)
> return;
>
> mutex_lock(&ps->pinst->lock);
> list_del(&ps->list);
> - padata_free_pd(rcu_dereference_protected(ps->pd, 1));
> + pd = rcu_dereference_protected(ps->pd, 1);
> + if (refcount_dec_and_test(&pd->refcnt))
> + padata_free_pd(rcu_dereference_protected(ps->pd, 1));
As Herbert points out, this version changes the code by
rcu-dereferencing pd twice. Usually previous acks are dropped when
introducing new changes, but you can have it back by only
rcu-dereferencing once and addressing the other comments above.
> mutex_unlock(&ps->pinst->lock);
>
> kfree(ps);
> --
> 2.40.0
>