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    Subject[PATCH 4.14 63/88] unfuck sysfs_mount()
    Date
    From: Al Viro <viro@zeniv.linux.org.uk>

    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@zeniv.linux.org.uk>
    Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    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;
    --
    2.30.2
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