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 <bianpan2016@xxxxxxx>
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?
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 <jack@xxxxxxxx>
SUSE Labs, CR
