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Message-ID: <20241127.Ob8DaeR9xaul@digikod.net>
Date: Wed, 27 Nov 2024 13:10:01 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Mimi Zohar <zohar@...ux.ibm.com>
Cc: Al Viro <viro@...iv.linux.org.uk>,
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linux-security-module@...r.kernel.org
Subject: Re: [PATCH v21 6/6] samples/check-exec: Add an enlighten "inc"
interpreter and 28 tests
On Tue, Nov 26, 2024 at 12:41:45PM -0500, Mimi Zohar wrote:
> 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.
It makes sense. Could you please send a patch for these
IMA-*-interpreter changes? I'll include it in the next series.
>
>
> > >
> > > > + 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);
> > > > +}
> > > > +
> > >
> > >
> >
>
>
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