On 10/14/2014 07:25 AM, Seth Forshee wrote:
> Unprivileged users are normally restricted from mounting with the
> allow_other option by system policy, but this could be bypassed
> for a mount done with user namespace root permissions. In such
> cases allow_other should not allow users outside the user
> namespace to access the mount as doing so would give the
> unprivileged user the ability to manipulate processes it would
> otherwise be unable to manipulate.
What threat is this intended to protect against? I think that, if this
is needed, tasks outside the userns or its descendents should be
blocked, even if the user ids match. That is, I think you should check
the namespace, not the uid and gid.
--Andy
>
> Cc: Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@xxxxxxxxxxxxxxxx>
> Cc: Serge H. Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@xxxxxxxxxxxxxxxx>
> Signed-off-by: Seth Forshee <seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@xxxxxxxxxxxxxxxx>
> ---
> fs/fuse/dir.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index 123db1e06c78..e3123bfbc711 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -1089,12 +1089,20 @@ int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid,
> */
> int fuse_allow_current_process(struct fuse_conn *fc)
> {
> - const struct cred *cred;
> + const struct cred *cred = current_cred();
>
> - if (fc->flags & FUSE_ALLOW_OTHER)
> - return 1;
> + if (fc->flags & FUSE_ALLOW_OTHER) {
> + if (kuid_has_mapping(fc->user_ns, cred->euid) &&
> + kuid_has_mapping(fc->user_ns, cred->suid) &&
> + kuid_has_mapping(fc->user_ns, cred->uid) &&
> + kgid_has_mapping(fc->user_ns, cred->egid) &&
> + kgid_has_mapping(fc->user_ns, cred->sgid) &&
> + kgid_has_mapping(fc->user_ns, cred->gid))
> + return 1;
> +
> + return 0;
> + }
>
> - cred = current_cred();
> if (uid_eq(cred->euid, fc->user_id) &&
> uid_eq(cred->suid, fc->user_id) &&
> uid_eq(cred->uid, fc->user_id) &&
>
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