On Tue, Nov 27, 2018 at 10:25:51AM +0100, Jan Kara wrote:
> On Sun 25-11-18 08:15:23, Pan Bian wrote:
> > After calling dput(new_dentry), new_dentry is passed to fsnotify_move.
> > This may result in a use-after-free bug. This patch moves the put
> > operation late.
> >
> > Fixes: da1ce0670c14("vfs: add cross-rename")
> > Signed-off-by: Pan Bian <bianpan2...@163.com>
>
> The code is actually fine AFAICT. One new_dentry reference is passed into
> vfs_rename() and another one is acquired directly inside vfs_rename(). That
> is the one dropped early but there's still the original reference passed in
> protecting new_dentry from freeing. Am I missing something?
I am not quite sure about the actual execution logic. But I guess new_dentry
reference may be dropped outside vfs_rename in cocurrent executions.
Otherwise, there is no need to acquire & drop new_dentry reference as it
is always alive along vfs_rename.
Best regards,
Pan
>
> Honza
>
> > ---
> > V2: correct the fixes commit information
> > ---
> > fs/namei.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/namei.c b/fs/namei.c
> > index 0cab649..8b104d9 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -4498,7 +4498,6 @@ int vfs_rename(struct inode *old_dir, struct dentry
> > *old_dentry,
> > unlock_two_nondirectories(source, target);
> > else if (target)
> > inode_unlock(target);
> > - dput(new_dentry);
> > if (!error) {
> > fsnotify_move(old_dir, new_dir, old_name.name, is_dir,
> > !(flags & RENAME_EXCHANGE) ? target : NULL,
> > old_dentry);
> > @@ -4507,6 +4506,7 @@ int vfs_rename(struct inode *old_dir, struct dentry
> > *old_dentry,
> > new_is_dir, NULL, new_dentry);
> > }
> > }
> > + dput(new_dentry);
> > release_dentry_name_snapshot(&old_name);
> >
> > return error;
> > --
> > 2.7.4
> >
> >
> --
> Jan Kara <j...@suse.com>
> SUSE Labs, CR
