linux-kernel - Re: [GIT PULL] execve updates for v6.13-rc1

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Message-ID: <20241121024112.GN3387508@ZenIV>
Date: Thu, 21 Nov 2024 02:41:12 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <kees@...nel.org>, linux-kernel@...r.kernel.org,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Nir Lichtman <nir@...htman.org>,
	syzbot+03e1af5c332f7e0eb84b@...kaller.appspotmail.com,
	Tycho Andersen <tandersen@...flix.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>
Subject: Re: [GIT PULL] execve updates for v6.13-rc1

On Thu, Nov 21, 2024 at 02:36:19AM +0000, Al Viro wrote:
> On Wed, Nov 20, 2024 at 02:50:39PM -0800, Linus Torvalds wrote:
> > So you probably want to do something like
> > 
> >         const char *name = smp_load_acquire(&dentry->d_name.name);
> > 
> > under the RCU read lock before then copying it with strscpy(). It
> > should always be NULL-terminated.
> > 
> > If you want to be extra careful, you might surround it with a
> > 
> >         read_seqbegin_or_lock(&rename_lock, &seq);
> 
> What for?
> 
> 	char name[something];
> 
> 	sprintf(name, "%*pD", sizeof(name) - 1, file);
> 
> and be done with that...

... or

	struct name_snapshot n;

	take_dentry_name_snapshot(&n, file->f_path.dentry);

	do_something(n.name.name);

	release_dentry_name_snapshot(&n);