linux-kernel - Re: security/loadpin: Allow to exclude specific file types

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Message-ID: <201905310740.522B3A7C1@keescook>
Date:   Fri, 31 May 2019 07:44:17 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     Ke Wu <mikewu@...gle.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: security/loadpin: Allow to exclude specific file types

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@...gle.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.

-- 
Kees Cook