[PATCH 4.14 63/88] unfuck sysfs_mount()

From: Sasha Levin
Date: Mon Jun 28 2021 - 11:13:15 EST

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

commit 7b745a4e4051e1bbce40e0b1c2cf636c70583aa4 upstream.

new_sb is left uninitialized in case of early failures in kernfs_mount_ns(),
and while IS_ERR(root) is true in all such cases, using IS_ERR(root) || !new_sb
is not a solution - IS_ERR(root) is true in some cases when new_sb is true.

Make sure new_sb is initialized (and matches the reality) in all cases and
fix the condition for dropping kobj reference - we want it done precisely
in those situations where the reference has not been transferred into a new
super_block instance.

Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
fs/sysfs/mount.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 20b8f82e115b..2bbe84d9c0a8 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -28,7 +28,7 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
struct dentry *root;
void *ns;
- bool new_sb;
+ bool new_sb = false;

if (!(flags & MS_KERNMOUNT)) {
if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
@@ -38,9 +38,9 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
root = kernfs_mount_ns(fs_type, flags, sysfs_root,
SYSFS_MAGIC, &new_sb, ns);
- if (IS_ERR(root) || !new_sb)
+ if (!new_sb)
kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
- else if (new_sb)
+ else if (!IS_ERR(root))
root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;

return root;