On Sat, Aug 17, 2019 at 12:13:50PM -0300, Rafael Neves wrote:
> Hi,
>
> Submitting to tech@ to broader audience.
>
> When using -P option in mfs with a directory or a block device that
> doen't exist, for example when the device roams, newfs(2) leaves
> leftovers of temporary mount points.
>
> With my /etc/fstab:
> ca7552589896b01e.b none swap sw
> ca7552589896b01e.a / ffs rw 1 1
> ca7552589896b01e.k /home ffs rw,nodev,nosuid 1 2
> #ca7552589896b01e.d /tmp ffs rw,nodev,nosuid 1 2
> swap /tmp mfs rw,nodev,nosuid,-s=300M 0 0
> ca7552589896b01e.f /usr ffs rw,nodev 1 2
> ca7552589896b01e.g /usr/X11R6 ffs rw,nodev 1 2
> ca7552589896b01e.h /usr/local ffs rw,nodev,wxallowed 1 2
> ca7552589896b01e.j /usr/build ffs rw,noperm,noauto 1 2
> swap /usr/obj mfs rw,nodev,nosuid,noauto,-s=4G,-P=/foo/bar 0 0
> ca7552589896b01e.i /usr/src ffs rw,nodev,nosuid 1 2
> ca7552589896b01e.e /var ffs rw,nodev,nosuid 1 2
>
> Result when trying to mount /usr/obj:
> root@orus [rneves]# mount /usr/obj
> mount_mfs: cannot stat /foo/bar: No such file or directory
> root@orus [rneves]# mount
> /dev/sd2a on / type ffs (local)
> /dev/sd2k on /home type ffs (local, nodev, nosuid)
> mfs:28249 on /tmp type mfs (asynchronous, local, nodev, nosuid,
> size=614400 512-blocks)
> /dev/sd2f on /usr type ffs (local, nodev)
> /dev/sd2g on /usr/X11R6 type ffs (local, nodev)
> /dev/sd2h on /usr/local type ffs (local, nodev, wxallowed)
> /dev/sd2i on /usr/src type ffs (local, nodev, nosuid)
> /dev/sd2e on /var type ffs (local, nodev, nosuid)
> mfs:44634 on /tmp/mntoMG6WmZTT7 type mfs (asynchronous, local, nodev,
> nosuid, size=8388608 512-blocks)
>
>
> Tracking down the issue I found that:
> + When -P is specified, pop != NULL.
> + After fork, waitformount() is called. It creates the temporary
> places to store the data.
> + copy() is called, and it it fails the following umount() and
> rmdir() is not called, leaving the temporary mounts.
>
> As copy() can fail in a couple of ways, I thought about the following change:
> + Make all errors a warning, but after then return to the first
> caller indicating an error. Getting the erro the clean up is
> done, and exit(1).
>
> + Make copy() return an int: -1 in fail, and 0 otherwise.
> + isdir(), gettmpmnt(): Convert errors to warnings + return(-1).
>
> There is a change of messages printing if you don't have a /tmp
> is read-only, first the error of cannot fstat, and after
> "Cannot create tmp mountpoint for -P".
>
> There still a chance to get a inconsistent state: if there is no
> /bin/pax, or errors in do_exec(). But erros in do_exec seem very
> critical, the same with a missing /bin/pax. So I didn't change them.
>
> Otto@ said that another alternative is using atexit(3), but we
> pointed out what it is very difficult to get it right, and almost
> always has race conditions. Given that and what manpage says I have no
> hope that I can get it right.
>
> What do you think?
>
> Note that the check in line 519 (newfs.c) was changed to add the new
> possible return value. Actually, currently it is not allowed -P with a
> read-only /tmp, because in this case gettmpmnt() returns 0, and by this
> early check newfs(2) throws an error. Actually, gettmpmnt() must changed
> to it work properly. The `created` if uses a <= by symmetry.
>
> But this is a differente issue, that I think could be changed in a
> separated diff.
>
> Regards,
> Rafael Neves
>
>
> Patch:
>
>
> Index: newfs.c
> ===================================================================
> RCS file: /cvs/src/sbin/newfs/newfs.c,v
> retrieving revision 1.112
> diff -u -p -r1.112 newfs.c
> --- newfs.c 28 Jun 2019 13:32:45 -0000 1.112
> +++ newfs.c 17 Aug 2019 14:27:46 -0000
> @@ -147,7 +147,7 @@ struct disklabel *getdisklabel(char *, i
> static void waitformount(char *, pid_t);
> static int do_exec(const char *, const char *, char *const[]);
> static int isdir(const char *);
> -static void copy(char *, char *);
> +static int copy(char *, char *);
> static int gettmpmnt(char *, size_t);
> #endif
>
> @@ -179,6 +179,7 @@ main(int argc, char *argv[])
> #ifdef MFS
> char mountfromname[BUFSIZ];
> char *pop = NULL, node[PATH_MAX];
> + int ret;
Please move this one inside the scope where it is used, see below
> pid_t pid;
> struct stat mountpoint;
> #endif
> @@ -516,7 +517,7 @@ havelabel:
> struct mfs_args args;
> char tmpnode[PATH_MAX];
here
>
> - if (pop != NULL && gettmpmnt(tmpnode, sizeof(tmpnode)) == 0)
> + if (pop != NULL && gettmpmnt(tmpnode, sizeof(tmpnode)) <= 0)
> errx(1, "Cannot create tmp mountpoint for -P");
> memset(&args, 0, sizeof(args));
> args.base = membase;
> @@ -537,9 +538,11 @@ havelabel:
> default:
> if (pop != NULL) {
> waitformount(tmpnode, pid);
> - copy(pop, tmpnode);
> + ret = copy(pop, tmpnode);
> unmount(tmpnode, 0);
> rmdir(tmpnode);
> + if (ret == -1)
> + exit(1);
> }
> waitformount(node, pid);
It might be an idea to undo the mount an return 1 if ret is != 0.
For that to work ret should be initialized to 0.
-Otto
> exit(0);
> @@ -740,14 +743,18 @@ isdir(const char *path)
> {
> struct stat st;
>
> - if (stat(path, &st) != 0)
> - err(1, "cannot stat %s", path);
> - if (!S_ISDIR(st.st_mode) && !S_ISBLK(st.st_mode))
> - errx(1, "%s: not a dir or a block device", path);
> + if (stat(path, &st) != 0) {
> + warn("cannot stat %s", path);
> + return (-1);
> + }
> + if (!S_ISDIR(st.st_mode) && !S_ISBLK(st.st_mode)) {
> + warn("%s: not a dir or a block device", path);
> + return (-1);
> + }
> return (S_ISDIR(st.st_mode));
> }
>
> -static void
> +static int
> copy(char *src, char *dst)
> {
> int ret, dir, created = 0;
> @@ -755,11 +762,16 @@ copy(char *src, char *dst)
> char mountpoint[MNAMELEN];
> char *const argv[] = { "pax", "-rw", "-pe", ".", dst, NULL } ;
>
> - dir = isdir(src);
> + if ((dir = isdir(src)) == -1)
> + return (-1);
> +
> if (dir)
> strlcpy(mountpoint, src, sizeof(mountpoint));
> else {
> created = gettmpmnt(mountpoint, sizeof(mountpoint));
> + if (created <= 0)
> + return (-1);
> +
> memset(&mount_args, 0, sizeof(mount_args));
> mount_args.fspec = src;
> ret = mount(MOUNT_FFS, mountpoint, MNT_RDONLY, &mount_args);
> @@ -769,7 +781,8 @@ copy(char *src, char *dst)
> warn("rmdir %s", mountpoint);
> if (unmount(dst, 0) != 0)
> warn("unmount %s", dst);
> - errc(1, saved_errno, "mount %s %s", src, mountpoint);
> + warnc(saved_errno, "mount %s %s", src, mountpoint);
> + return (-1);
> }
> }
> ret = do_exec(mountpoint, "/bin/pax", argv);
> @@ -780,8 +793,10 @@ copy(char *src, char *dst)
> if (ret != 0) {
> if (unmount(dst, 0) != 0)
> warn("unmount %s", dst);
> - errx(1, "copy %s to %s failed", mountpoint, dst);
> + warnx("copy %s to %s failed", mountpoint, dst);
> + return (-1);
> }
> + return (0);
> }
>
> static int
> @@ -792,27 +807,42 @@ gettmpmnt(char *mountpoint, size_t len)
> struct statfs fs;
> size_t n;
>
> - if (statfs(tmp, &fs) != 0)
> - err(1, "statfs %s", tmp);
> + if (statfs(tmp, &fs) != 0) {
> + warn("statfs %s", tmp);
> + return (-1);
> + }
> +
> if (fs.f_flags & MNT_RDONLY) {
> - if (statfs(mnt, &fs) != 0)
> - err(1, "statfs %s", mnt);
> - if (strcmp(fs.f_mntonname, "/") != 0)
> - errx(1, "tmp mountpoint %s busy", mnt);
> - if (strlcpy(mountpoint, mnt, len) >= len)
> - errx(1, "tmp mountpoint %s too long", mnt);
> + if (statfs(mnt, &fs) != 0) {
> + warn("statfs %s", mnt);
> + return (-1);
> + }
> + if (strcmp(fs.f_mntonname, "/") != 0) {
> + warnx("tmp mountpoint %s busy", mnt);
> + return (-1);
> + }
> + if (strlcpy(mountpoint, mnt, len) >= len) {
> + warnx("tmp mountpoint %s too long", mnt);
> + return (-1);
> + }
> return (0);
> }
> n = strlcpy(mountpoint, tmp, len);
> - if (n >= len)
> - errx(1, "tmp mount point too long");
> + if (n >= len) {
> + warnx("tmp mount point too long");
> + return (-1);
> + }
> if (mountpoint[n - 1] != '/')
> strlcat(mountpoint, "/", len);
> n = strlcat(mountpoint, "mntXXXXXXXXXX", len);
> - if (n >= len)
> - errx(1, "tmp mount point too long");
> - if (mkdtemp(mountpoint) == NULL)
> - err(1, "mkdtemp %s", mountpoint);
> + if (n >= len) {
> + warnx("tmp mount point too long");
> + return (-1);
> + }
> + if (mkdtemp(mountpoint) == NULL) {
> + warn("mkdtemp %s", mountpoint);
> + return (-1);
> + }
> return (1);
> }
>
>
