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
there).
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index 55605c5..edac42c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1237,6 +1237,14 @@
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 @@
if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
return -EINVAL;
+ if (!may_mount())
+ return -EPERM;
+
if (!(flags & UMOUNT_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
@@ -1268,10 +1279,6 @@
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);
dput_and_out:
/* we mustn't call path_put() as that would clear mnt_expiry_mark */
@@ -1295,7 +1302,7 @@
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 @@
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 @@
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 @@
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 @@
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);