From 3151527ee007b73a0ebd296010f1c0454a919c7d Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 15 Mar 2013 01:45:51 -0700 Subject: userns: Don't allow creation if the user is chrooted Guarantee that the policy of which files may be access that is established by setting the root directory will not be violated by user namespaces by verifying that the root directory points to the root of the mount namespace at the time of user namespace creation. Changing the root is a privileged operation, and as a matter of policy it serves to limit unprivileged processes to files below the current root directory. For reasons of simplicity and comprehensibility the privilege to change the root directory is gated solely on the CAP_SYS_CHROOT capability in the user namespace. Therefore when creating a user namespace we must ensure that the policy of which files may be access can not be violated by changing the root directory. Anyone who runs a processes in a chroot and would like to use user namespace can setup the same view of filesystems with a mount namespace instead. With this result that this is not a practical limitation for using user namespaces. Cc: stable@vger.kernel.org Acked-by: Serge Hallyn Reported-by: Andy Lutomirski Signed-off-by: "Eric W. Biederman" --- fs/namespace.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'fs') diff --git a/fs/namespace.c b/fs/namespace.c index 50ca17d3cb4..a3035223d42 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2732,6 +2732,30 @@ bool our_mnt(struct vfsmount *mnt) return check_mnt(real_mount(mnt)); } +bool current_chrooted(void) +{ + /* Does the current process have a non-standard root */ + struct path ns_root; + struct path fs_root; + bool chrooted; + + /* Find the namespace root */ + ns_root.mnt = ¤t->nsproxy->mnt_ns->root->mnt; + ns_root.dentry = ns_root.mnt->mnt_root; + path_get(&ns_root); + while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root)) + ; + + get_fs_root(current->fs, &fs_root); + + chrooted = !path_equal(&fs_root, &ns_root); + + path_put(&fs_root); + path_put(&ns_root); + + return chrooted; +} + static void *mntns_get(struct task_struct *task) { struct mnt_namespace *ns = NULL; -- cgit v1.2.3-70-g09d2 From 90563b198e4c6674c63672fae1923da467215f45 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 22 Mar 2013 03:10:15 -0700 Subject: vfs: Add a mount flag to lock read only bind mounts When a read-only bind mount is copied from mount namespace in a higher privileged user namespace to a mount namespace in a lesser privileged user namespace, it should not be possible to remove the the read-only restriction. Add a MNT_LOCK_READONLY mount flag to indicate that a mount must remain read-only. CC: stable@vger.kernel.org Acked-by: Serge Hallyn Signed-off-by: "Eric W. Biederman" --- fs/namespace.c | 3 +++ include/linux/mount.h | 2 ++ 2 files changed, 5 insertions(+) (limited to 'fs') diff --git a/fs/namespace.c b/fs/namespace.c index a3035223d42..8505b5ece5d 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1713,6 +1713,9 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags) if (readonly_request == __mnt_is_readonly(mnt)) return 0; + if (mnt->mnt_flags & MNT_LOCK_READONLY) + return -EPERM; + if (readonly_request) error = mnt_make_readonly(real_mount(mnt)); else diff --git a/include/linux/mount.h b/include/linux/mount.h index d7029f4a191..73005f9957e 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -47,6 +47,8 @@ struct mnt_namespace; #define MNT_INTERNAL 0x4000 +#define MNT_LOCK_READONLY 0x400000 + struct vfsmount { struct dentry *mnt_root; /* root of the mounted tree */ struct super_block *mnt_sb; /* pointer to superblock */ -- cgit v1.2.3-70-g09d2 From 132c94e31b8bca8ea921f9f96a57d684fa4ae0a9 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 22 Mar 2013 04:08:05 -0700 Subject: 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 Reported-by: Andy Lutomirski Signed-off-by: "Eric W. Biederman" --- fs/namespace.c | 6 +++++- fs/pnode.c | 6 ++++++ fs/pnode.h | 1 + 3 files changed, 12 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/namespace.c b/fs/namespace.c index 8505b5ece5d..968d4c5eae0 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); diff --git a/fs/pnode.c b/fs/pnode.c index 3e000a51ac0..8b29d2164da 100644 --- a/fs/pnode.c +++ b/fs/pnode.c @@ -9,6 +9,7 @@ #include #include #include +#include #include "internal.h" #include "pnode.h" @@ -220,6 +221,7 @@ static struct mount *get_source(struct mount *dest, int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry, struct mount *source_mnt, struct list_head *tree_list) { + struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns; struct mount *m, *child; int ret = 0; struct mount *prev_dest_mnt = dest_mnt; @@ -237,6 +239,10 @@ int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry, source = get_source(m, prev_dest_mnt, prev_src_mnt, &type); + /* Notice when we are propagating across user namespaces */ + if (m->mnt_ns->user_ns != user_ns) + type |= CL_UNPRIVILEGED; + child = copy_tree(source, source->mnt.mnt_root, type); if (IS_ERR(child)) { ret = PTR_ERR(child); diff --git a/fs/pnode.h b/fs/pnode.h index 19b853a3445..a0493d5ebfb 100644 --- a/fs/pnode.h +++ b/fs/pnode.h @@ -23,6 +23,7 @@ #define CL_MAKE_SHARED 0x08 #define CL_PRIVATE 0x10 #define CL_SHARED_TO_SLAVE 0x20 +#define CL_UNPRIVILEGED 0x40 static inline void set_mnt_shared(struct mount *mnt) { -- cgit v1.2.3-70-g09d2 From 87a8ebd637dafc255070f503909a053cf0d98d3f Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sun, 24 Mar 2013 14:28:27 -0700 Subject: userns: Restrict when proc and sysfs can be mounted Only allow unprivileged mounts of proc and sysfs if they are already mounted when the user namespace is created. proc and sysfs are interesting because they have content that is per namespace, and so fresh mounts are needed when new namespaces are created while at the same time proc and sysfs have content that is shared between every instance. Respect the policy of who may see the shared content of proc and sysfs by only allowing new mounts if there was an existing mount at the time the user namespace was created. In practice there are only two interesting cases: proc and sysfs are mounted at their usual places, proc and sysfs are not mounted at all (some form of mount namespace jail). Cc: stable@vger.kernel.org Acked-by: Serge Hallyn Signed-off-by: "Eric W. Biederman" --- fs/namespace.c | 21 +++++++++++++++++++++ fs/proc/root.c | 4 ++++ fs/sysfs/mount.c | 4 ++++ include/linux/user_namespace.h | 4 ++++ kernel/user.c | 2 ++ kernel/user_namespace.c | 2 ++ 6 files changed, 37 insertions(+) (limited to 'fs') diff --git a/fs/namespace.c b/fs/namespace.c index 968d4c5eae0..d581e45c0a9 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2763,6 +2763,27 @@ bool current_chrooted(void) return chrooted; } +void update_mnt_policy(struct user_namespace *userns) +{ + struct mnt_namespace *ns = current->nsproxy->mnt_ns; + struct mount *mnt; + + down_read(&namespace_sem); + list_for_each_entry(mnt, &ns->list, mnt_list) { + switch (mnt->mnt.mnt_sb->s_magic) { + case SYSFS_MAGIC: + userns->may_mount_sysfs = true; + break; + case PROC_SUPER_MAGIC: + userns->may_mount_proc = true; + break; + } + if (userns->may_mount_sysfs && userns->may_mount_proc) + break; + } + up_read(&namespace_sem); +} + static void *mntns_get(struct task_struct *task) { struct mnt_namespace *ns = NULL; diff --git a/fs/proc/root.c b/fs/proc/root.c index c6e9fac26ba..9c7fab1d23f 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -108,6 +109,9 @@ static struct dentry *proc_mount(struct file_system_type *fs_type, } else { ns = task_active_pid_ns(current); options = data; + + if (!current_user_ns()->may_mount_proc) + return ERR_PTR(-EPERM); } sb = sget(fs_type, proc_test_super, proc_set_super, flags, ns); diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c index 8d924b5ec73..afd83273e6c 100644 --- a/fs/sysfs/mount.c +++ b/fs/sysfs/mount.c @@ -19,6 +19,7 @@ #include #include #include +#include #include "sysfs.h" @@ -111,6 +112,9 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type, struct super_block *sb; int error; + if (!(flags & MS_KERNMOUNT) && !current_user_ns()->may_mount_sysfs) + return ERR_PTR(-EPERM); + info = kzalloc(sizeof(*info), GFP_KERNEL); if (!info) return ERR_PTR(-ENOMEM); diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 4ce00932493..b6b215f13b4 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -26,6 +26,8 @@ struct user_namespace { kuid_t owner; kgid_t group; unsigned int proc_inum; + bool may_mount_sysfs; + bool may_mount_proc; }; extern struct user_namespace init_user_ns; @@ -82,4 +84,6 @@ static inline void put_user_ns(struct user_namespace *ns) #endif +void update_mnt_policy(struct user_namespace *userns); + #endif /* _LINUX_USER_H */ diff --git a/kernel/user.c b/kernel/user.c index e81978e8c03..8e635a18ab5 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -51,6 +51,8 @@ struct user_namespace init_user_ns = { .owner = GLOBAL_ROOT_UID, .group = GLOBAL_ROOT_GID, .proc_inum = PROC_USER_INIT_INO, + .may_mount_sysfs = true, + .may_mount_proc = true, }; EXPORT_SYMBOL_GPL(init_user_ns); diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 0f1e4288457..a54f26f82eb 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -96,6 +96,8 @@ int create_user_ns(struct cred *new) set_cred_user_ns(new, ns); + update_mnt_policy(ns); + return 0; } -- cgit v1.2.3-70-g09d2