I sent out a new patch according to your last suggestion. Please take
a look. Thanks!


On Fri, May 31, 2019 at 1:33 PM Kees Cook [off-list ref] wrote:

On Fri, May 31, 2019 at 11:03:17AM -0700, Ke Wu wrote:

quoted

I think Coverity is correct. Note that it's the size of
kernel_read_file_str (rather than exclude_read_files) doesn't equal to
ignore_read_file_id.

This is because READING_MAX_ID is also an element in
kernel_read_file_str, which makes the size of kernel_read_file_str to
be READING_MAX_ID+1. I will send a new patch to fix the issue. Thanks
for the  analysis!

Ah! Yes, I see now. I was looking at the wrong things. It should be
possible to just do:

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209                for (j = 0; j < ARRAY_SIZE(kernel_read_file_str); j++) {

for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++)

and add a

BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) < ARRAY_SIZE(ignore_read_file_id))

for future robustness checking.

Thanks for looking at this more closely!

-Kees

quoted

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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

--
Ke Wu | Software Engineer | mikewu@google.com | Google Inc.

--
Kees Cook

-- 
Ke Wu | Software Engineer | mikewu@google.com | Google Inc.