Commit 9b40bc90 authored by Al Viro's avatar Al Viro

get rid of unprotected dereferencing of mnt->mnt_ns

It's safe only under namespace_sem or vfsmount_lock; all places
in fs/namespace.c that want mnt->mnt_ns->user_ns actually want to use
current->nsproxy->mnt_ns->user_ns (note the calls of check_mnt() in

Signed-off-by: default avatarAl Viro <>
parent 3a142ed9
......@@ -1237,6 +1237,14 @@ static int do_umount(struct mount *mnt, int flags)
return retval;
* Is the caller allowed to modify his namespace?
static inline bool may_mount(void)
return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
* Now umount can handle mount points as well as block devices.
* This is important for filesystems which use unnamed block devices.
......@@ -1255,6 +1263,9 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
return -EINVAL;
if (!may_mount())
return -EPERM;
if (!(flags & UMOUNT_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
......@@ -1268,10 +1279,6 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
if (!check_mnt(mnt))
goto dput_and_out;
retval = -EPERM;
if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))
goto dput_and_out;
retval = do_umount(mnt, flags);
/* we mustn't call path_put() as that would clear mnt_expiry_mark */
......@@ -1295,7 +1302,7 @@ SYSCALL_DEFINE1(oldumount, char __user *, name)
static int mount_is_safe(struct path *path)
if (ns_capable(real_mount(path->mnt)->mnt_ns->user_ns, CAP_SYS_ADMIN))
if (may_mount())
return 0;
return -EPERM;
#ifdef notyet
......@@ -1633,7 +1640,7 @@ static int do_change_type(struct path *path, int flag)
int type;
int err = 0;
if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))
if (!may_mount())
return -EPERM;
if (path->dentry != path->mnt->mnt_root)
......@@ -1797,7 +1804,7 @@ static int do_move_mount(struct path *path, const char *old_name)
struct mount *p;
struct mount *old;
int err = 0;
if (!ns_capable(real_mount(path->mnt)->mnt_ns->user_ns, CAP_SYS_ADMIN))
if (!may_mount())
return -EPERM;
if (!old_name || !*old_name)
return -EINVAL;
......@@ -1933,16 +1940,14 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
int mnt_flags, const char *name, void *data)
struct file_system_type *type;
struct user_namespace *user_ns;
struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
struct vfsmount *mnt;
int err;
if (!fstype)
return -EINVAL;
/* we need capabilities... */
user_ns = real_mount(path->mnt)->mnt_ns->user_ns;
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
if (!may_mount())
return -EPERM;
type = get_fs_type(fstype);
......@@ -2567,7 +2572,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
struct mount *new_mnt, *root_mnt;
int error;
if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
if (!may_mount())
return -EPERM;
error = user_path_dir(new_root, &new);
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