linux-kernel - Re: [PATCH RFC namespace] Fix uninitialized uflags in SYSCALL_DEFINE5(move

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Message-ID: <d8c20a28-2dc4-4b9d-bea0-0800aea0de30@paulmck-laptop>
Date: Thu, 27 Feb 2025 09:29:12 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Christian Brauner <brauner@...nel.org>
Cc: viro@...iv.linux.org.uk, jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, sfr@...b.auug.org.au,
	linux-next@...r.kernel.org
Subject: Re: [PATCH RFC namespace] Fix uninitialized uflags in
 SYSCALL_DEFINE5(move_mount)

On Thu, Feb 27, 2025 at 09:13:10AM +0100, Christian Brauner wrote:
> On Wed, Feb 26, 2025 at 11:18:49AM -0800, Paul E. McKenney wrote:
> > The next-20250226 release gets an uninitialized-variable warning from the
> > move_mount syscall in builds with clang 19.1.5.  This variable is in fact
> > assigned only if the MOVE_MOUNT_F_EMPTY_PATH flag is set, but is then
> > unconditionally passed to getname_maybe_null(), which unconditionally
> > references it.
> > 
> > This patch simply sets uflags to zero in the same manner as is done
> > for lflags, which makes rcutorture happy, but might or might not be a
> > proper patch.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Alexander Viro <viro@...iv.linux.org.uk>
> > Cc: Christian Brauner <brauner@...nel.org>
> > Cc: Jan Kara <jack@...e.cz>
> > Cc: <linux-fsdevel@...r.kernel.org>
> > Cc: <linux-kernel@...r.kernel.org>
> > ---
> 
> Hey Paul! Thank you for the patch. The fix is correct but I've already
> taken a patch from Arnd yesterday. So hopefully you'll forgive me for
> not taking yours. :)

Thank you, and looking forward to seeing -next being fixed.  I guess I
just need to be faster.  ;-)

							Thanx, Paul

> >  namespace.c |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/fs/namespace.c b/fs/namespace.c
> > index 663bacefddfa6..80505d533cd23 100644
> > --- a/fs/namespace.c
> > +++ b/fs/namespace.c
> > @@ -4617,6 +4617,7 @@ SYSCALL_DEFINE5(move_mount,
> >  	if (flags & MOVE_MOUNT_BENEATH)		mflags |= MNT_TREE_BENEATH;
> >  
> >  	lflags = 0;
> > +	uflags = 0;
> >  	if (flags & MOVE_MOUNT_F_SYMLINKS)	lflags |= LOOKUP_FOLLOW;
> >  	if (flags & MOVE_MOUNT_F_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;
> >  	if (flags & MOVE_MOUNT_F_EMPTY_PATH)	uflags = AT_EMPTY_PATH;
> > @@ -4625,6 +4626,7 @@ SYSCALL_DEFINE5(move_mount,
> >  		return PTR_ERR(from_name);
> >  
> >  	lflags = 0;
> > +	uflags = 0;
> >  	if (flags & MOVE_MOUNT_T_SYMLINKS)	lflags |= LOOKUP_FOLLOW;
> >  	if (flags & MOVE_MOUNT_T_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;
> >  	if (flags & MOVE_MOUNT_T_EMPTY_PATH)	uflags = AT_EMPTY_PATH;