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SubjectRe: [RFC][PATCH 4/3] vfs: Allow rmdir to remove mounts in all but the current mount namespace
Quoting Eric W. Biederman (ebiederm@xmission.com):
>
> Programs have been known to test for empty directories by attempting
> to remove them. To keep from violating the principle of least
> surprise don't let directories the caller can see with someting
> mounted on them be deleted.

Do you think we should do the same thing for over-mounted file at
vfs_unlink()?

> With a little luck this may prevent commands stupid commands
> like rm -rf from eating your system.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> fs/namei.c | 21 +++++++++++++++++++++
> 1 files changed, 21 insertions(+), 0 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index b18b017c946b..b9cae480ac27 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3547,6 +3547,20 @@ void dentry_unhash(struct dentry *dentry)
> spin_unlock(&dentry->d_lock);
> }
>
> +static bool covered(struct vfsmount *mnt, struct dentry *dentry)
> +{
> + /* test to see if a dentry is covered with a mount in
> + * the current mount namespace.
> + */
> + bool is_covered;
> +
> + rcu_read_lock();
> + is_covered = d_mountpoint(dentry) && __lookup_mnt(mnt, dentry, 1);
> + rcu_read_unlock();
> +
> + return is_covered;
> +}
> +
> int vfs_rmdir(struct inode *dir, struct dentry *dentry)
> {
> int error = may_delete(dir, dentry, 1);
> @@ -3619,6 +3633,9 @@ retry:
> error = -ENOENT;
> goto exit3;
> }
> + error = -EBUSY;
> + if (covered(nd.path.mnt, dentry))
> + goto exit3;
> error = security_path_rmdir(&nd.path, dentry);
> if (error)
> goto exit3;
> @@ -4155,6 +4172,10 @@ retry:
> error = -ENOTEMPTY;
> if (new_dentry == trap)
> goto exit5;
> + error = -EBUSY;
> + if (new_dentry->d_inode && S_ISDIR(new_dentry->d_inode->i_mode) &&
> + covered(newnd.path.mnt, new_dentry))
> + goto exit5;
>
> error = security_path_rename(&oldnd.path, old_dentry,
> &newnd.path, new_dentry);
> --
> 1.7.5.4


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