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(+) diff --git a/fs/namespace.c b/fs/namespace.c index a3035223d421..8505b5ece5de 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 d7029f4a191a..73005f9957ea 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 v1.2.3-58-ga151