linux-kernel - Re: [PATCH v2 1/1] selinux: fix another double free

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Message-ID: <d8cee44a-316f-d1be-9893-428598ada2d8@redhat.com>
Date:   Thu, 11 Jun 2020 15:41:11 -0700
From:   Tom Rix <trix@...hat.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Ondrej Mosnacek <omosnace@...hat.com>, weiyongjun1@...wei.com,
        selinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] selinux: fix another double free


On 6/11/20 3:30 PM, Paul Moore wrote:
> On Thu, Jun 11, 2020 at 4:48 PM <trix@...hat.com> wrote:
>> From: Tom Rix <trix@...hat.com>
>>
>> Clang static analysis reports this double free error
>>
>> security/selinux/ss/conditional.c:139:2: warning: Attempt to free released memory [unix.Malloc]
>>         kfree(node->expr.nodes);
>>         ^~~~~~~~~~~~~~~~~~~~~~~
>>
>> When cond_read_node fails, it calls cond_node_destroy which frees the
>> node but does not poison the entry in the node list.  So when it
>> returns to its caller cond_read_list, cond_read_list deletes the
>> partial list.  The latest entry in the list will be deleted twice.
>>
>> So instead of freeing the node in cond_read_node, let list freeing in
>> code_read_list handle the freeing the problem node along with all of the
>> earlier nodes.
>>
>> Because cond_read_node no longer does any error handling, the goto's
>> the error case are redundant.  Instead just return the error code.
>>
>> Fixes a problem was introduced by commit
>>
>>   selinux: convert cond_list to array
>>
>> Signed-off-by: Tom Rix <trix@...hat.com>
>> ---
>>  security/selinux/ss/conditional.c | 11 +++--------
>>  1 file changed, 3 insertions(+), 8 deletions(-)
> Hi Tom,
>
> Thanks for the patch!  A few more notes, in no particular order:
>
> * There is no need to send a cover letter for just a single patch.
> Typically cover letters are reserved for large patchsets that require
> some additional explanation and/or instructions beyond the individual
> commit descriptions.

I was doing this to carry the repo name and tag info.

So how do folks know which repo and commit the change applies to ?

> * Thank you for including a changelog with your patch updates, but it
> would be helpful if you included them in the patch by using a "---"
> delimiter in the commit description after your signoff but before the
> diffstat.  Here is a recent example:
> -> https://lore.kernel.org/selinux/20200611135303.19538-3-cgzones@googlemail.com
Ok got it.
>
> * When referencing a patch which you are "fixing", the proper syntax
> is 'Fixes: <12char_commitID> ("<subject_line")'.  Look at commit
> 46619b44e431 in Linus' tree to see an example.

Ok

> If you have any questions, let us know.