[ 079/150] get rid of unprotected dereferencing of mnt->mnt_ns

Greg Kroah-Hartman
2013-02-27T01:00:51Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit 9b40bc90abd126bcc5da5658059b8e72e285e559 upstream.

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).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/namespace.c | 29 +++++++++++++++++------------
1 file changed, 17 insertions(+), 12 deletions(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1237,6 +1237,14 @@ static int do_umount(struct mount *mnt,
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 *, n
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 @@ SYSCALL_DEFINE2(umount, char __user *, n
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 @@ SYSCALL_DEFINE1(oldumount, char __user *

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 *p
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 *pa
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 *pat
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 _
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);