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Subject: Re: [PATCH] Use an IDR to allocate apparmor secids
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-kernel@vger.kernel.org
References: <20180522093259.GA30182@bombadil.infradead.org>
 <20180528170108.GA5448@bombadil.infradead.org>
From:   John Johansen <john.johansen@canonical.com>
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Organization: Canonical
Message-ID: <862d03b6-ba2f-3ec0-d45e-d8fcf16f9edf@canonical.com>
Date:   Mon, 4 Jun 2018 18:27:09 -0700
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On 05/28/2018 10:01 AM, Matthew Wilcox wrote:
> 
> ping?
> 
> I have this queued up in my XArray tree.  If I don't hear from you before
> -rc1, I'll be submitting it as part of the XArray conversion.
> 
hey Mathew,

I've pulled this into apparmor-next and done the retuning of
AA_SECID_INVALID a follow on patch. The reworking of the api to
return the specific error type can wait for another cycle.


> On Tue, May 22, 2018 at 02:32:59AM -0700, Matthew Wilcox wrote:
>> Replace the custom usage of the radix tree to store a list of free IDs
>> with the IDR.
>>
>> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
>>
>>  security/apparmor/secid.c |  114 ++++------------------------------------------
>>  1 file changed, 11 insertions(+), 103 deletions(-)
>>
>> diff --git a/security/apparmor/secid.c b/security/apparmor/secid.c
>> index c2f0c1571156..3ad94b2ffbb2 100644
>> --- a/security/apparmor/secid.c
>> +++ b/security/apparmor/secid.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/errno.h>
>>  #include <linux/err.h>
>>  #include <linux/gfp.h>
>> +#include <linux/idr.h>
>>  #include <linux/slab.h>
>>  #include <linux/spinlock.h>
>>  
>> @@ -30,18 +31,10 @@
>>  /*
>>   * secids - do not pin labels with a refcount. They rely on the label
>>   * properly updating/freeing them
>> - *
>> - * A singly linked free list is used to track secids that have been
>> - * freed and reuse them before allocating new ones
>>   */
>>  
>> -#define FREE_LIST_HEAD 1
>> -
>> -static RADIX_TREE(aa_secids_map, GFP_ATOMIC);
>> +static DEFINE_IDR(aa_secids);
>>  static DEFINE_SPINLOCK(secid_lock);
>> -static u32 alloced_secid = FREE_LIST_HEAD;
>> -static u32 free_list = FREE_LIST_HEAD;
>> -static unsigned long free_count;
>>  
>>  /*
>>   * TODO: allow policy to reserve a secid range?
>> @@ -49,65 +42,6 @@ static unsigned long free_count;
>>   * TODO: use secid_update in label replace
>>   */
>>  
>> -#define SECID_MAX U32_MAX
>> -
>> -/* TODO: mark free list as exceptional */
>> -static void *to_ptr(u32 secid)
>> -{
>> -	return (void *)
>> -		((((unsigned long) secid) << RADIX_TREE_EXCEPTIONAL_SHIFT));
>> -}
>> -
>> -static u32 to_secid(void *ptr)
>> -{
>> -	return (u32) (((unsigned long) ptr) >> RADIX_TREE_EXCEPTIONAL_SHIFT);
>> -}
>> -
>> -
>> -/* TODO: tag free_list entries to mark them as different */
>> -static u32 __pop(struct aa_label *label)
>> -{
>> -	u32 secid = free_list;
>> -	void __rcu **slot;
>> -	void *entry;
>> -
>> -	if (free_list == FREE_LIST_HEAD)
>> -		return AA_SECID_INVALID;
>> -
>> -	slot = radix_tree_lookup_slot(&aa_secids_map, secid);
>> -	AA_BUG(!slot);
>> -	entry = radix_tree_deref_slot_protected(slot, &secid_lock);
>> -	free_list = to_secid(entry);
>> -	radix_tree_replace_slot(&aa_secids_map, slot, label);
>> -	free_count--;
>> -
>> -	return secid;
>> -}
>> -
>> -static void __push(u32 secid)
>> -{
>> -	void __rcu **slot;
>> -
>> -	slot = radix_tree_lookup_slot(&aa_secids_map, secid);
>> -	AA_BUG(!slot);
>> -	radix_tree_replace_slot(&aa_secids_map, slot, to_ptr(free_list));
>> -	free_list = secid;
>> -	free_count++;
>> -}
>> -
>> -static struct aa_label * __secid_update(u32 secid, struct aa_label *label)
>> -{
>> -	struct aa_label *old;
>> -	void __rcu **slot;
>> -
>> -	slot = radix_tree_lookup_slot(&aa_secids_map, secid);
>> -	AA_BUG(!slot);
>> -	old = radix_tree_deref_slot_protected(slot, &secid_lock);
>> -	radix_tree_replace_slot(&aa_secids_map, slot, label);
>> -
>> -	return old;
>> -}
>> -
>>  /**
>>   * aa_secid_update - update a secid mapping to a new label
>>   * @secid: secid to update
>> @@ -115,11 +49,10 @@ static struct aa_label * __secid_update(u32 secid, struct aa_label *label)
>>   */
>>  void aa_secid_update(u32 secid, struct aa_label *label)
>>  {
>> -	struct aa_label *old;
>>  	unsigned long flags;
>>  
>>  	spin_lock_irqsave(&secid_lock, flags);
>> -	old = __secid_update(secid, label);
>> +	idr_replace(&aa_secids, label, secid);
>>  	spin_unlock_irqrestore(&secid_lock, flags);
>>  }
>>  
>> @@ -132,7 +65,7 @@ struct aa_label *aa_secid_to_label(u32 secid)
>>  	struct aa_label *label;
>>  
>>  	rcu_read_lock();
>> -	label = radix_tree_lookup(&aa_secids_map, secid);
>> +	label = idr_find(&aa_secids, secid);
>>  	rcu_read_unlock();
>>  
>>  	return label;
>> @@ -167,7 +100,6 @@ int apparmor_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
>>  	return 0;
>>  }
>>  
>> -
>>  int apparmor_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
>>  {
>>  	struct aa_label *label;
>> @@ -186,7 +118,6 @@ void apparmor_release_secctx(char *secdata, u32 seclen)
>>  	kfree(secdata);
>>  }
>>  
>> -
>>  /**
>>   * aa_alloc_secid - allocate a new secid for a profile
>>   */
>> @@ -195,35 +126,12 @@ u32 aa_alloc_secid(struct aa_label *label, gfp_t gfp)
>>  	unsigned long flags;
>>  	u32 secid;
>>  
>> -	/* racey, but at worst causes new allocation instead of reuse */
>> -	if (free_list == FREE_LIST_HEAD) {
>> -		bool preload = 0;
>> -		int res;
>> -
>> -retry:
>> -		if (gfpflags_allow_blocking(gfp) && !radix_tree_preload(gfp))
>> -			preload = 1;
>> -		spin_lock_irqsave(&secid_lock, flags);
>> -		if (alloced_secid != SECID_MAX) {
>> -			secid = ++alloced_secid;
>> -			res = radix_tree_insert(&aa_secids_map, secid, label);
>> -			AA_BUG(res == -EEXIST);
>> -		} else {
>> -			secid = AA_SECID_INVALID;
>> -		}
>> -		spin_unlock_irqrestore(&secid_lock, flags);
>> -		if (preload)
>> -			radix_tree_preload_end();
>> -	} else {
>> -		spin_lock_irqsave(&secid_lock, flags);
>> -		/* remove entry from free list */
>> -		secid = __pop(label);
>> -		if (secid == AA_SECID_INVALID) {
>> -			spin_unlock_irqrestore(&secid_lock, flags);
>> -			goto retry;
>> -		}
>> -		spin_unlock_irqrestore(&secid_lock, flags);
>> -	}
>> +	idr_preload(gfp);
>> +	spin_lock_irqsave(&secid_lock, flags);
>> +	secid = idr_alloc(&aa_secids, label, 0, 0, GFP_ATOMIC);
>> +	/* XXX: Can return -ENOMEM */
>> +	spin_unlock_irqrestore(&secid_lock, flags);
>> +	idr_preload_end();
>>  
>>  	return secid;
>>  }
>> @@ -237,6 +145,6 @@ void aa_free_secid(u32 secid)
>>  	unsigned long flags;
>>  
>>  	spin_lock_irqsave(&secid_lock, flags);
>> -	__push(secid);
>> +	idr_remove(&aa_secids, secid);
>>  	spin_unlock_irqrestore(&secid_lock, flags);
>>  }
>>