linux-kernel - Re: Are setuid shell scripts safe? (Implied by security_bprm_creds_for

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Message-ID: <20251204054915.GI1712166@ZenIV>
Date: Thu, 4 Dec 2025 05:49:15 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Bernd Edlinger <bernd.edlinger@...mail.de>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
	Roberto Sassu <roberto.sassu@...weicloud.com>,
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	apparmor <apparmor@...ts.ubuntu.com>
Subject: Re: Are setuid shell scripts safe? (Implied by
 security_bprm_creds_for_exec)

On Wed, Dec 03, 2025 at 02:16:29PM +0100, Bernd Edlinger wrote:

> Hmm, yes, that looks like an issue.
> 
> I would have expected the security engine to look at bprm->filenanme
> especially in the case, when bprm->interp != bprm->filename,
> and check that it is not a sym-link with write-access for the
> current user and of course also that the bprm->file is not a regular file
> which is writable by the current user, if that is the case I would have expected
> the secuity engine to enforce non-new-privs on a SUID executable somehow.

Check that _what_ is not a symlink?  And while we are at it, what do write
permissions to any symlinks have to do with anything whatsoever?