linux-kernel - Re: [Test Failure Report] exec: Test failures in execveat

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Date: Tue, 5 Mar 2024 13:00:58 -0800
From: Kees Cook <keescook@...omium.org>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: Eric Biederman <ebiederm@...ssion.com>, Shuah Khan <shuah@...nel.org>,
	Mark Brown <broonie@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	"kernel@...labora.com" <kernel@...labora.com>
Subject: Re: [Test Failure Report] exec: Test failures in execveat

On Tue, Mar 05, 2024 at 07:20:27PM +0500, Muhammad Usama Anjum wrote:
> Hello,
> 
> I've been running execveat (execveat.c) locally on v6.1 and next-20240228.
> It has flaky test case. There are some test cases which fail consistently.
> The comment (not very clear) on top of failing cases is as following:
> 
> /*
>  * Execute as a long pathname relative to "/".  If this is a script,
>  * the interpreter will launch but fail to open the script because its
>  * name ("/dev/fd/5/xxx....") is bigger than PATH_MAX.
>  *
>  * The failure code is usually 127 (POSIX: "If a command is not found,
>  * the exit status shall be 127."), but some systems give 126 (POSIX:
>  * "If the command name is found, but it is not an executable utility,
>  * the exit status shall be 126."), so allow either.
>  */
> The file name is just less than PATH_MAX (4096) and we are expecting the
> execveat() to fail with particular 99 or 127/128 error code. But kernel is
> returning 1 error code. Snippet from full output:
> 
> # child 3493092 exited with 1 not 99 nor 99
> # child 3493094 exited with 1 not 127 nor 126
> 
> I'm not sure if test is wrong or the kernel has changed the return error codes.

The error code is actually coming from the script interpreter (in this
case, "/bin/sh"). On my system, /bin/sh is /bin/dash, and I see the
failure. If I manually change "script" to use "#!/bin/bash", the test
passes for me.

Since lots of other selftests appears to depend on /bin/bash, I think
the right fix is simply:


diff --git a/tools/testing/selftests/exec/execveat.c b/tools/testing/selftests/exec/execveat.c
index bf79d664c8e6..0546ca24f2b2 100644
--- a/tools/testing/selftests/exec/execveat.c
+++ b/tools/testing/selftests/exec/execveat.c
@@ -393,7 +393,7 @@ static int run_tests(void)
 static void prerequisites(void)
 {
 	int fd;
-	const char *script = "#!/bin/sh\nexit $*\n";
+	const char *script = "#!/bin/bash\nexit $*\n";
 
 	/* Create ephemeral copies of files */
 	exe_cp("execveat", "execveat.ephemeral");


Can you test this and let me know if this fixes it for you?

Thanks for the report!

-Kees

-- 
Kees Cook