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mnt: Refactor the logic for mounting sysfs and proc in a user namespace

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Fresh mounts of proc and sysfs are a very special case that works very
much like a bind mount.  Unfortunately the current structure can not
preserve the MNT_LOCK... mount flags.  Therefore refactor the logic
into a form that can be modified to preserve those lock bits.

Add a new filesystem flag FS_USERNS_VISIBLE that requires some mount
of the filesystem be fully visible in the current mount namespace,
before the filesystem may be mounted.

Move the logic for calling fs_fully_visible from proc and sysfs into
fs/namespace.c where it has greater access to mount namespace state.

Cc: [email protected]
Signed-off-by: "Eric W. Biederman" <[email protected]>
This commit is contained in:
Eric W. Biederman 2015-05-08 23:22:29 -05:00
commit 1b852bceb0
4 changed files with 10 additions and 10 deletions
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8
fs/namespace.c
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@ -2332,6 +2332,8 @@ unlock:
return err;
}
static bool fs_fully_visible(struct file_system_type *fs_type);
/*
* create a new mount for userspace and request it to be added into the
* namespace's tree
@ -2363,6 +2365,10 @@ 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))
return -EPERM;
}
}
mnt = vfs_kern_mount(type, flags, name, data);
@ -3164,7 +3170,7 @@ bool current_chrooted(void)
return chrooted;
}
bool fs_fully_visible(struct file_system_type *type)
static bool fs_fully_visible(struct file_system_type *type)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
struct mount *mnt;