linux-kernel - Re: [PATCH] samples/landlock: fix path

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Message-ID: <fb03aba8-8556-804f-72b8-c7cbf7155226@digikod.net>
Date:   Wed, 28 Apr 2021 20:04:57 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Tom Rix <trix@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        linux-security-module@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        James Morris <jmorris@...ei.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] samples/landlock: fix path_list memory leak


On 28/04/2021 17:36, Tom Rix wrote:
> 
> On 4/28/21 2:58 AM, Mickaël Salaün wrote:
>> On 27/04/2021 21:13, Nick Desaulniers wrote:
>>> On Tue, Apr 27, 2021 at 11:38 AM <trix@...hat.com> wrote:
>>>> From: Tom Rix <trix@...hat.com>
>>>>
>>>> Clang static analysis reports this error
>>>>
>>>> sandboxer.c:134:8: warning: Potential leak of memory
>>>>    pointed to by 'path_list'
>>>>          ret = 0;
>>>>                ^
>>>> path_list is allocated in parse_path() but never freed.
>>>>
>>>> Signed-off-by: Tom Rix <trix@...hat.com>
>>>> ---
>>>>   samples/landlock/sandboxer.c | 2 ++
>>>>   1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/samples/landlock/sandboxer.c
>>>> b/samples/landlock/sandboxer.c
>>>> index 7a15910d2171..4629d011ed61 100644
>>>> --- a/samples/landlock/sandboxer.c
>>>> +++ b/samples/landlock/sandboxer.c
>>>> @@ -134,6 +134,8 @@ static int populate_ruleset(
>>>>          ret = 0;
>>>>
>>>>   out_free_name:
>>>> +       if (path_list)
>>>> +               free(path_list);
>>> I don't think the conditional is even necessary? By our first `goto
>>> out_free_name;`, `parse_path` has already been called/memory for
>>> `path_list` has already been allocated. `parse_path` doesn't check
>>> whether `malloc` has failed.
>> Indeed, no need for the path_list check. In practice, this memory leak
>> doesn't stay long because of the execve, but I missed this free anyway.
>> Thanks!
> 
> Ok, the general problem of not checking if malloc and friends succeeds
> is a different problem.
> 
> So remove the check and keep the free ?

Yes please.

> 
> Tom
> 
>> Reviewed-by: Mickaël Salaün <mic@...ux.microsoft.com>
>>
>>>>          free(env_path_name);
>>>>          return ret;
>>>>   }
>>>> -- 
>>>> 2.26.3
>>>>
>>>
>