linux-kernel - Re: [PATCH] tomoyo: Avoid potential null pointer access

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Message-ID: <01d29bbf-9d77-c787-b2c2-d88a6a5047f7@huawei.com>
Date:   Thu, 26 Nov 2020 14:33:55 +0800
From:   Zheng Zengkai <zhengzengkai@...wei.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
CC:     <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <jmorris@...ei.org>,
        <serge@...lyn.com>, <weiyongjun1@...wei.com>
Subject: Re: [PATCH] tomoyo: Avoid potential null pointer access

Hello, Tetsuo

Got it , Thank you for your explanation.

> Hello, Zheng.
>
> Thank you for a patch, but I won't apply this patch.
> Expected behavior is that tomoyo_warn_oom() is called
> if tomoyo_memory_ok() is called with entry == NULL.
>
> Adding __GFP_NOWARN might be OK, but returning without tomoyo_warn_oom() is NG.
>
> On 2020/11/25 21:10, Zheng Zengkai wrote:
>> Calls to kzalloc() should be null-checked in order to avoid
>> any potential failures or unnecessary code execution.
>> Fix this by adding null checks for _entry_ right after allocation.
>>
>> Fixes: 57c2590fb7fd ("TOMOYO: Update profile structure")
>> Reported-by: Hulk Robot <hulkci@...wei.com>
>> Signed-off-by: Zheng Zengkai <zhengzengkai@...wei.com>
> Nacked-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

As your say,  I found the function tomoyo_assign_namespace( )

in security/tomoyo/domain.c has the similar situation,

Can I add __GFP_NOWARN for both and remove the null check for _entry_ in 
tomoyo_assign_namespace( )?

diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index 4bee32bfe16d..bc54d3c8c70a 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -498,7 +498,7 @@ static struct tomoyo_profile *tomoyo_assign_profile
         ptr = ns->profile_ptr[profile];
         if (ptr)
                 return ptr;
-       entry = kzalloc(sizeof(*entry), GFP_NOFS);
+       entry = kzalloc(sizeof(*entry), GFP_NOFS | __GFP_NOWARN);
         if (mutex_lock_interruptible(&tomoyo_policy_lock))
                 goto out;
         ptr = ns->profile_ptr[profile];
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index dc4ecc0b2038..c6e5cc5cc7cd 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -473,9 +473,7 @@ struct tomoyo_policy_namespace 
*tomoyo_assign_namespace(const char *domainname)
                 return ptr;
         if (len >= TOMOYO_EXEC_TMPSIZE - 10 || 
!tomoyo_domain_def(domainname))
                 return NULL;
-       entry = kzalloc(sizeof(*entry) + len + 1, GFP_NOFS);
-       if (!entry)
-               return NULL;
+       entry = kzalloc(sizeof(*entry) + len + 1, GFP_NOFS | __GFP_NOWARN);
         if (mutex_lock_interruptible(&tomoyo_policy_lock))
                 goto out;
         ptr = tomoyo_find_namespace(domainname, len);

>> ---
>>   security/tomoyo/common.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
>> index 4bee32bfe16d..99b4fafcb100 100644
>> --- a/security/tomoyo/common.c
>> +++ b/security/tomoyo/common.c
>> @@ -499,6 +499,8 @@ static struct tomoyo_profile *tomoyo_assign_profile
>>   	if (ptr)
>>   		return ptr;
>>   	entry = kzalloc(sizeof(*entry), GFP_NOFS);
>> +	if (!entry)
>> +		return NULL;
>>   	if (mutex_lock_interruptible(&tomoyo_policy_lock))
>>   		goto out;
>>   	ptr = ns->profile_ptr[profile];
>>
> .
>