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From: Vijayanand Jitta <>
To: Uladzislau Rezki <>
Subject: Re: [PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases
Date: Wed, 24 Mar 2021 08:59:37 +0530	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210318165907.GA10448@pc638.lan>

On 3/18/2021 10:29 PM, Uladzislau Rezki wrote:
> On Thu, Mar 18, 2021 at 03:38:25PM +0530, wrote:
>> From: Vijayanand Jitta <>
>> 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.

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  reply	other threads:[~2021-03-24  3:29 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-18 10:08 [PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases vjitta
2021-03-18 16:59 ` Uladzislau Rezki
2021-03-24  3:29   ` Vijayanand Jitta [this message]
2021-03-24 13:32     ` Uladzislau Rezki

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