From: Miklos Szeredi Add a new mount flag "nomnt", which denies submounts for the owner. This would be useful, if we want to support traditional /etc/fstab based user mounts. In this case mount(8) would still have to be suid-root, to check the mountpoint against the user/users flag in /etc/fstab, but /etc/mtab would no longer be mandatory for storing the actual owner of the mount. Signed-off-by: Miklos Szeredi Cc: Ram Pai Cc: Christoph Hellwig Signed-off-by: Andrew Morton --- fs/namespace.c | 8 +++++++- include/linux/fs.h | 1 + include/linux/mount.h | 1 + 3 files changed, 9 insertions(+), 1 deletion(-) diff -puN fs/namespace.c~unprivileged-mounts-add-no-submounts-flag fs/namespace.c --- a/fs/namespace.c~unprivileged-mounts-add-no-submounts-flag +++ a/fs/namespace.c @@ -435,6 +435,7 @@ static int show_vfsmnt(struct seq_file * { MNT_NOATIME, ",noatime" }, { MNT_NODIRATIME, ",nodiratime" }, { MNT_RELATIME, ",relatime" }, + { MNT_NOMNT, ",nomnt" }, { 0, NULL } }; struct proc_fs_info *fs_infop; @@ -781,6 +782,9 @@ static bool permit_mount(struct nameidat if (S_ISLNK(inode->i_mode)) return false; + if (nd->mnt->mnt_flags & MNT_NOMNT) + return false; + if (!is_mount_owner(nd->mnt, current->fsuid)) return false; @@ -1550,9 +1554,11 @@ long do_mount(char *dev_name, char *dir_ mnt_flags |= MNT_NODIRATIME; if (flags & MS_RELATIME) mnt_flags |= MNT_RELATIME; + if (flags & MS_NOMNT) + mnt_flags |= MNT_NOMNT; flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | - MS_NOATIME | MS_NODIRATIME | MS_RELATIME); + MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_NOMNT); /* ... and get the mountpoint */ retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd); diff -puN include/linux/fs.h~unprivileged-mounts-add-no-submounts-flag include/linux/fs.h --- a/include/linux/fs.h~unprivileged-mounts-add-no-submounts-flag +++ a/include/linux/fs.h @@ -129,6 +129,7 @@ extern int dir_notify_enable; #define MS_RELATIME (1<<21) /* Update atime relative to mtime/ctime. */ #define MS_NO_LEASES (1<<22) /* fs does not support leases */ #define MS_SETUSER (1<<23) /* set mnt_uid to current user */ +#define MS_NOMNT (1<<24) /* don't allow unprivileged submounts */ #define MS_ACTIVE (1<<30) #define MS_NOUSER (1<<31) diff -puN include/linux/mount.h~unprivileged-mounts-add-no-submounts-flag include/linux/mount.h --- a/include/linux/mount.h~unprivileged-mounts-add-no-submounts-flag +++ a/include/linux/mount.h @@ -28,6 +28,7 @@ struct mnt_namespace; #define MNT_NOATIME 0x08 #define MNT_NODIRATIME 0x10 #define MNT_RELATIME 0x20 +#define MNT_NOMNT 0x40 #define MNT_SHRINKABLE 0x100 #define MNT_USER 0x200 _