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authorEric W. Biederman <ebiederm@xmission.com>2013-03-22 04:08:05 -0700
committerEric W. Biederman <ebiederm@xmission.com>2013-03-27 07:50:05 -0700
commit132c94e31b8bca8ea921f9f96a57d684fa4ae0a9 (patch)
tree52db12073a31f62301367416b2a3afec185975ef /fs/namespace.c
parent90563b198e4c6674c63672fae1923da467215f45 (diff)
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vfs: Carefully propogate mounts across user namespaces
As a matter of policy MNT_READONLY should not be changable if the original mounter had more privileges than creator of the mount namespace. Add the flag CL_UNPRIVILEGED to note when we are copying a mount from a mount namespace that requires more privileges to a mount namespace that requires fewer privileges. When the CL_UNPRIVILEGED flag is set cause clone_mnt to set MNT_NO_REMOUNT if any of the mnt flags that should never be changed are set. This protects both mount propagation and the initial creation of a less privileged mount namespace. Cc: stable@vger.kernel.org Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'fs/namespace.c')
-rw-r--r--fs/namespace.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 8505b5e..968d4c5 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -798,6 +798,10 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
}
mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~MNT_WRITE_HOLD;
+ /* Don't allow unprivileged users to change mount flags */
+ if ((flag & CL_UNPRIVILEGED) && (mnt->mnt.mnt_flags & MNT_READONLY))
+ mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
+
atomic_inc(&sb->s_active);
mnt->mnt.mnt_sb = sb;
mnt->mnt.mnt_root = dget(root);
@@ -2342,7 +2346,7 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
/* First pass: copy the tree topology */
copy_flags = CL_COPY_ALL | CL_EXPIRE;
if (user_ns != mnt_ns->user_ns)
- copy_flags |= CL_SHARED_TO_SLAVE;
+ copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
new = copy_tree(old, old->mnt.mnt_root, copy_flags);
if (IS_ERR(new)) {
up_write(&namespace_sem);