2021-02-05 01:06:09

by Daniel Latypov

Subject: [PATCH v2 3/3] kunit: tool: fix unintentional statefulness in run_kernel()

This is a bug that has been present since the first version of this
code.
Using [] as a default parameter is dangerous, since it's mutable.

Example using the REPL:
>>> def bad(param = []):
... param.append(len(param))
... print(param)
...
>>> bad()
[0]
>>> bad()
[0, 1]

This wasn't a concern in the past since it would just keep appending the
same values to it.

E.g. before, `args` would just grow in size like:
[mem=1G', 'console=tty']
[mem=1G', 'console=tty', mem=1G', 'console=tty']

But with now filter_glob, this is more dangerous, e.g.
run_kernel(filter_glob='my-test*') # default modified here
run_kernel() # filter_glob still applies here!
That earlier `filter_glob` will affect all subsequent calls that don't
specify `args`.

Note: currently the kunit tool only calls run_kernel() at most once, so
it's not possible to trigger any negative side-effects right now.

Fixes: 6ebf5866f2e8 ("kunit: tool: add Python wrappers for running KUnit tests")
Signed-off-by: Daniel Latypov <[email protected]>
---
tools/testing/kunit/kunit_kernel.py | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/kunit/kunit_kernel.py b/tools/testing/kunit/kunit_kernel.py
index 71b1942f5ccd..6dd3cf6e8efa 100644
--- a/tools/testing/kunit/kunit_kernel.py
+++ b/tools/testing/kunit/kunit_kernel.py
@@ -199,7 +199,9 @@ class LinuxSourceTree(object):
return False
return self.validate_config(build_dir)

- def run_kernel(self, args=[], build_dir='', filter_glob='', timeout=None) -> Iterator[str]:
+ def run_kernel(self, args=None, build_dir='', filter_glob='', timeout=None) -> Iterator[str]:
+ if not args:
+ args = []
args.extend(['mem=1G', 'console=tty'])
if filter_glob:
args.append('kunit.filter_glob='+filter_glob)
--
2.30.0.365.g02bc693789-goog

2021-02-05 01:45:19

by Brendan Higgins

Subject: Re: [PATCH v2 3/3] kunit: tool: fix unintentional statefulness in run_kernel()

On Thu, Feb 4, 2021 at 9:31 AM Daniel Latypov <[email protected]> wrote:
>
> This is a bug that has been present since the first version of this
> code.
> Using [] as a default parameter is dangerous, since it's mutable.
>
> Example using the REPL:
> >>> def bad(param = []):
> ... param.append(len(param))
> ... print(param)
> ...
> >>> bad()
> [0]
> >>> bad()
> [0, 1]
>
> This wasn't a concern in the past since it would just keep appending the
> same values to it.
>
> E.g. before, `args` would just grow in size like:
> [mem=1G', 'console=tty']
> [mem=1G', 'console=tty', mem=1G', 'console=tty']
>
> But with now filter_glob, this is more dangerous, e.g.
> run_kernel(filter_glob='my-test*') # default modified here
> run_kernel() # filter_glob still applies here!
> That earlier `filter_glob` will affect all subsequent calls that don't
> specify `args`.
>
> Note: currently the kunit tool only calls run_kernel() at most once, so
> it's not possible to trigger any negative side-effects right now.
>
> Fixes: 6ebf5866f2e8 ("kunit: tool: add Python wrappers for running KUnit tests")
> Signed-off-by: Daniel Latypov <[email protected]>

Whoah, nice catch! I didn't even know that was a thing!

Reviewed-by: Brendan Higgins <[email protected]>