On 3/18/2021 10:29 PM, Uladzislau Rezki wrote:
> On Thu, Mar 18, 2021 at 03:38:25PM +0530, vji...@codeaurora.org wrote:
>> From: Vijayanand Jitta <vji...@codeaurora.org>
>>
>> A potential use after free can occur in _vm_unmap_aliases
>> where an already freed vmap_area could be accessed, Consider
>> the following scenario:
>>
>> Process 1 Process 2
>>
>> __vm_unmap_aliases __vm_unmap_aliases
>> purge_fragmented_blocks_allcpus rcu_read_lock()
>> rcu_read_lock()
>> list_del_rcu(&vb->free_list)
>>
>> list_for_each_entry_rcu(vb .. )
>> __purge_vmap_area_lazy
>> kmem_cache_free(va)
>>
>> va_start = vb->va->va_start
> Or maybe we should switch to kfree_rcu() instead of kmem_cache_free()?
>
> --
> Vlad Rezki
>
Thanks for suggestion.
I see free_vmap_area_lock (spinlock) is taken in __purge_vmap_area_lazy
while it loops through list and calls kmem_cache_free on va's. So, looks
like we can't replace it with kfree_rcu as it might cause scheduling
within atomic context.
Thanks,
Vijay
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