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Subject: Re: security/loadpin: Allow to exclude specific file types
To:     Kees Cook <keescook@chromium.org>
Cc:     Ke Wu <mikewu@google.com>,
        James Morris <jamorris@linux.microsoft.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        linux-security-module@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <73fac64c-fe49-4738-49a4-0afe668eed94@canonical.com>
 <201905310740.522B3A7C1@keescook>
From:   Colin Ian King <colin.king@canonical.com>
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Message-ID: <c80362bd-1dec-3e4f-c3e8-1c58d3a33070@canonical.com>
Date:   Fri, 31 May 2019 15:49:17 +0100
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On 31/05/2019 15:44, Kees Cook wrote:
> On Fri, May 31, 2019 at 11:46:29AM +0100, Colin Ian King wrote:
>> Hi,
>>
>> Static analysis with Coverity on linux-next has found a potential issue
>> with the following commit:
>>
>> commit 1633a4f04cc171fc638deb5c95af96032d3c591b
>> Author: Ke Wu <mikewu@google.com>
>> Date:   Thu May 30 12:22:08 2019 -0700
>>
>>     security/loadpin: Allow to exclude specific file types
>>
>>
>> 209                for (j = 0; j < ARRAY_SIZE(kernel_read_file_str); j++) {
>> 210                        if (strcmp(cur, kernel_read_file_str[j]) == 0) {
>> 211                                pr_info("excluding: %s\n",
>> 212                                        kernel_read_file_str[j]);
>>
>> CID 81977 (#1 of 1): Out-of-bounds write
>> overrun-local: Overrunning array ignore_read_file_id of 8 4-byte
>> elements at element index 8 (byte offset 35) using index j (which
>> evaluates to 8).
>>
>> 213                                ignore_read_file_id[j] = 1;
>>
>> According to Coverity ignore_read_file_id is an array of 8 integers.
>> However, ARRAY_SIZE(kernel_read_file_str) is 9, so we have an out of
>> bounds write on ignore_read_file[j] when j is 8.
> 
> What am I missing? This doesn't fail the build:
> 
> +       BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
> +                    ARRAY_SIZE(ignore_read_file_id));
> 
> They have the same number of elements.
> 

Yep, that's very true. I'll discuss this with Coverity as this seems
like a weird false positive.

Apologies for the noise.

Colin