linux-kernel - Re: [PATCH v21 6/6] samples/check-exec: Add an enlighten "inc" interpreter and 28 tests

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Message-ID: <623f89b4de41ac14e0e48e106b846abc9e9d70cf.camel@linux.ibm.com>
Date: Tue, 26 Nov 2024 12:41:45 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: Al Viro <viro@...iv.linux.org.uk>, Christian Brauner
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Subject: Re: [PATCH v21 6/6] samples/check-exec: Add an enlighten "inc"
 interpreter and 28 tests

On Fri, 2024-11-22 at 15:50 +0100, Mickaël Salaün wrote:
> On Thu, Nov 21, 2024 at 03:34:47PM -0500, Mimi Zohar wrote:
> > Hi Mickaël,
> > 
> > On Tue, 2024-11-12 at 20:18 +0100, Mickaël Salaün wrote:
> > > 
> > > +
> > > +/* Returns 1 on error, 0 otherwise. */
> > > +static int interpret_stream(FILE *script, char *const script_name,
> > > +			    char *const *const envp, const bool restrict_stream)
> > > +{
> > > +	int err;
> > > +	char *const script_argv[] = { script_name, NULL };
> > > +	char buf[128] = {};
> > > +	size_t buf_size = sizeof(buf);
> > > +
> > > +	/*
> > > +	 * We pass a valid argv and envp to the kernel to emulate a native
> > > +	 * script execution.  We must use the script file descriptor instead of
> > > +	 * the script path name to avoid race conditions.
> > > +	 */
> > > +	err = execveat(fileno(script), "", script_argv, envp,
> > > +		       AT_EMPTY_PATH | AT_EXECVE_CHECK);
> > 
> > At least with v20, the AT_CHECK always was being set, independent of whether
> > set-exec.c set it.  I'll re-test with v21.
> 
> AT_EXECVE_CEHCK should always be set, only the interpretation of the
> result should be relative to securebits.  This is highlighted in the
> documentation.

Sure, that sounds correct.  With an IMA-appraisal policy, any unsigned script
with the is_check flag set now emits an "cause=IMA-signature-required" audit
message.  However since IMA-appraisal isn't enforcing file signatures, this
sounds wrong.

New audit messages like "IMA-signature-required-by-interpreter" and "IMA-
signature-not-required-by-interpreter" would need to be defined based on the
SECBIT_EXEC_RESTRICT_FILE.


> > 
> > > +	if (err && restrict_stream) {
> > > +		perror("ERROR: Script execution check");
> > > +		return 1;
> > > +	}
> > > +
> > > +	/* Reads script. */
> > > +	buf_size = fread(buf, 1, buf_size - 1, script);
> > > +	return interpret_buffer(buf, buf_size);
> > > +}
> > > +
> > 
> > 
>