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mnt: Refactor fs_fully_visible into mount_too_revealing

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Replace the call of fs_fully_visible in do_new_mount from before the
new superblock is allocated with a call of mount_too_revealing after
the superblock is allocated.   This winds up being a much better location
for maintainability of the code.

The first change this enables is the replacement of FS_USERNS_VISIBLE
with SB_I_USERNS_VISIBLE.  Moving the flag from struct filesystem_type
to sb_iflags on the superblock.

Unfortunately mount_too_revealing fundamentally needs to touch
mnt_flags adding several MNT_LOCKED_XXX flags at the appropriate
times.  If the mnt_flags did not need to be touched the code
could be easily moved into the filesystem specific mount code.

Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman
2016-06-09 16:06:06 -05:00
parent 695e9df010
commit 8654df4e2a
5 changed files with 32 additions and 17 deletions
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38
fs/namespace.c
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@@ -2375,7 +2375,7 @@ unlock:
return err;
}
static bool fs_fully_visible(struct file_system_type *fs_type, int *new_mnt_flags);
static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
/*
* create a new mount for userspace and request it to be added into the
@@ -2408,12 +2408,6 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
flags |= MS_NODEV;
mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
}
if (type->fs_flags & FS_USERNS_VISIBLE) {
if (!fs_fully_visible(type, &mnt_flags)) {
put_filesystem(type);
return -EPERM;
}
}
}
mnt = vfs_kern_mount(type, flags, name, data);
@@ -2425,6 +2419,11 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
if (IS_ERR(mnt))
return PTR_ERR(mnt);
if (mount_too_revealing(mnt, &mnt_flags)) {
mntput(mnt);
return -EPERM;
}
err = do_add_mount(real_mount(mnt), path, mnt_flags);
if (err)
mntput(mnt);
@@ -3216,22 +3215,19 @@ bool current_chrooted(void)
return chrooted;
}
static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
int *new_mnt_flags)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
int new_flags = *new_mnt_flags;
struct mount *mnt;
bool visible = false;
if (unlikely(!ns))
return false;
down_read(&namespace_sem);
list_for_each_entry(mnt, &ns->list, mnt_list) {
struct mount *child;
int mnt_flags;
if (mnt->mnt.mnt_sb->s_type != type)
if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)
continue;
/* This mount is not fully visible if it's root directory
@@ -3298,6 +3294,22 @@ found:
return visible;
}
static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
unsigned long s_iflags;
if (ns->user_ns == &init_user_ns)
return false;
/* Can this filesystem be too revealing? */
s_iflags = mnt->mnt_sb->s_iflags;
if (!(s_iflags & SB_I_USERNS_VISIBLE))
return false;
return !mnt_already_visible(ns, mnt, new_mnt_flags);
}
static struct ns_common *mntns_get(struct task_struct *task)
{
struct ns_common *ns = NULL;