[Bug 1813001] Re: test_095_kernel_symbols_missing_proc_self_stack failed on P-LTS

Final reminder: We are at the end of the SRU Cycle and request that you
please provide verification the kernel in proposed resolves the problem
for which this bug was submitted. -Thank you!

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https://bugs.launchpad.net/bugs/1813001

Title:
test_095_kernel_symbols_missing_proc_self_stack failed on P-LTS

Status in ubuntu-kernel-tests:
In Progress
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Trusty:
Fix Committed

Bug description:
[Impact]

The testcase test_095_kernel_symbols_missing_proc_self_stack from
ubuntu_qrt_kernel_security testsuite started to fail with Trusty
kernel (3.13) after the fix for CVE-2018-17972 ("proc: restrict kernel
stack dumps to root"), which prevents a regular user to read from
/proc/self/stack.

Kernel: 3.13.0-165.215~precise1
The test failed with:
    AssertionError: cat: /proc/self/stack: Permission denied

FAIL: test_095_kernel_symbols_missing_proc_self_stack (__main__.KernelSecurityTest)
kernel addresses in /proc/self/stack are zeroed out
----------------------------------------------------------------------
Traceback (most recent call last):
File "./test-kernel-security.py", line 1364, in test_095_kernel_symbols_missing_proc_self_stack
self._check_pK_files(self._095_kernel_symbols_missing_proc_self_stack, expected=expected)
File "./test-kernel-security.py", line 1209, in _check_pK_files
test_function(expected_restricted)
File "./test-kernel-security.py", line 1320, in _095_kernel_symbols_missing_proc_self_stack
expected, retry=True)
File "./test-kernel-security.py", line 1146, in _read_twice
self.assertEqual(rc, 0, regular)
AssertionError: cat: /proc/self/stack: Permission denied

The testcase checks the file permission before trying to read it, and
for kernel 3.13 the permissions became inconsistent with what the user
can actually do:

$ cat /proc/self/stack
cat: /proc/self/stack: Permission denied
$ ls -l /proc/self/stack
-r--r--r-- 1 ubuntu ubuntu 0 Jan 24 04:06 /proc/self/stack

[Test Case]
Run 'cat' and 'ls' on the file as stated above, or run the ubuntu_qrt_kernel_security testsuite and check for the results of the test_095_kernel_symbols_missing_proc_self_stack testcase.

[Fix]
Upstream commit 35a35046e4f9 ("procfs: make /proc/*/{stack,syscall,personality} 0400") applied for v3.15-rc1 fixes the issue.

[Regression Potential]
The upstream fix changes the permissions of the files /proc/*/{stack,syscall,personality}, so userspace which relies on reading these files as regular users might fail. However, this fixes a security issue and is already applied on our later series.

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