From: Miklos Szeredi Allow bind mounts to unprivileged users if the following conditions are met: - mountpoint is not a symlink - parent mount is owned by the user - the number of user mounts is below the maximum Unprivileged mounts imply MS_SETUSER, and will also have the "nosuid" and "nodev" mount flags set. In particular, if mounting process doesn't have CAP_SETUID capability, then the "nosuid" flag will be added, and if it doesn't have CAP_MKNOD capability, then the "nodev" flag will be added. Signed-off-by: Miklos Szeredi Acked-by: Serge Hallyn --- Index: linux/fs/namespace.c =================================================================== --- linux.orig/fs/namespace.c 2008-02-04 23:47:58.000000000 +0100 +++ linux/fs/namespace.c 2008-02-04 23:48:00.000000000 +0100 @@ -545,6 +545,11 @@ static void __set_mnt_user(struct vfsmou WARN_ON(mnt->mnt_flags & MNT_USER); mnt->mnt_uid = current->fsuid; mnt->mnt_flags |= MNT_USER; + + if (!capable(CAP_SETUID)) + mnt->mnt_flags |= MNT_NOSUID; + if (!capable(CAP_MKNOD)) + mnt->mnt_flags |= MNT_NODEV; } static void set_mnt_user(struct vfsmount *mnt) @@ -1160,22 +1165,26 @@ asmlinkage long sys_oldumount(char __use #endif -static int mount_is_safe(struct nameidata *nd) +/* + * Conditions for unprivileged mounts are: + * - mountpoint is not a symlink + * - mountpoint is in a mount owned by the user + */ +static bool permit_mount(struct nameidata *nd, int *flags) { + struct inode *inode = nd->path.dentry->d_inode; + if (capable(CAP_SYS_ADMIN)) - return 0; - return -EPERM; -#ifdef notyet - if (S_ISLNK(nd->path.dentry->d_inode->i_mode)) - return -EPERM; - if (nd->path.dentry->d_inode->i_mode & S_ISVTX) { - if (current->uid != nd->path.dentry->d_inode->i_uid) - return -EPERM; - } - if (vfs_permission(nd, MAY_WRITE)) - return -EPERM; - return 0; -#endif + return true; + + if (S_ISLNK(inode->i_mode)) + return false; + + if (!is_mount_owner(nd->path.mnt, current->fsuid)) + return false; + + *flags |= MS_SETUSER; + return true; } static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry) @@ -1419,9 +1428,10 @@ static int do_loopback(struct nameidata int clone_fl; struct nameidata old_nd; struct vfsmount *mnt = NULL; - int err = mount_is_safe(nd); - if (err) - return err; + int err; + + if (!permit_mount(nd, &flags)) + return -EPERM; if (!old_name || !*old_name) return -EINVAL; err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd); -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/