Fix uninitialized uflags in SYSCALL_DEFINE5(move_mount)

[PATCH RFC namespace] Fix uninitialized uflags in SYSCALL_DEFINE5(move_mount)

Posted by Paul E. McKenney 11 months, 2 weeks ago

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@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: <linux-fsdevel@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
---
 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;

Re: [PATCH RFC namespace] Fix uninitialized uflags in SYSCALL_DEFINE5(move_mount)

Posted by Christian Brauner 11 months, 2 weeks ago

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@kernel.org>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Jan Kara <jack@suse.cz>
> Cc: <linux-fsdevel@vger.kernel.org>
> Cc: <linux-kernel@vger.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. :)

>  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;

Re: [PATCH RFC namespace] Fix uninitialized uflags in SYSCALL_DEFINE5(move_mount)

Posted by Paul E. McKenney 11 months, 2 weeks ago

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@kernel.org>
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: Christian Brauner <brauner@kernel.org>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: <linux-fsdevel@vger.kernel.org>
> > Cc: <linux-kernel@vger.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;