Take advantage of the use of file system IDs to simplify umount(8)

and make it work more reliably in a number of cases that have
traditionally been troublesome. The new behaviour is:
 1) If the filesystem can be determined by the fsid or device,
    or uniquely identified by the mountpoint, then just go ahead
    and call unmount(2) using the file system ID.
 2) Otherwise use fstatfs(2) to resolve the path into a file system
    ID (checking with stat(2) that it is a filesystem root directory).

Case 2 can potentially block if an NFS server is down, but it can
always be avoided by using an unambiguous specification. It handles
all the hard cases such as symlinks and mismatches between the mount
list and reality. For example, if a filesystem was mounted as /mnt
inside a chroot, it will show up in the mount list as /mnt, but now
you can unmount it from outside the chroot with "umount /chroot_path/mnt".

1 files changed, 144 insertions, 298 deletions

diff --git a/sbin/umount/umount.c b/sbin/umount/umount.c
index 209808c..18c920c 100644
--- a/sbin/umount/umount.c
+++ b/sbin/umount/umount.c
@@ -48,6 +48,7 @@ static const char rcsid[] =
 #include <sys/param.h>
 #include <sys/mount.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 
 #include <netdb.h>
 #include <rpc/rpc.h>
@@ -64,11 +65,7 @@ static const char rcsid[] =
 
 #include "mounttab.h"
 
-#define ISDOT(x)	((x)[0] == '.' && (x)[1] == '\0')
-#define ISDOTDOT(x)	((x)[0] == '.' && (x)[1] == '.' && (x)[2] == '\0')
-
-typedef enum { MNTON, MNTFROM, MNTFSID, NOTHING } mntwhat;
-typedef enum { MARK, UNMARK, NAME, COUNT, FREE } dowhat;
+typedef enum { FIND, REMOVE, CHECKUNIQUE } dowhat;
 
 struct  addrinfo *nfshost_ai = NULL;
 int	fflag, vflag;
@@ -76,15 +73,16 @@ char   *nfshost;
 
 struct statfs *checkmntlist(char *);
 int	 checkvfsname (const char *, char **);
-struct statfs *getmntentry(const char *, const char *, mntwhat, dowhat);
-char 	*getrealname(char *, char *resolved_path);
+struct statfs *getmntentry(const char *fromname, const char *onname,
+	     fsid_t *fsid, dowhat what);
 char   **makevfslist (const char *);
 size_t	 mntinfo (struct statfs **);
 int	 namematch (struct addrinfo *);
+int	 parsehexfsid(const char *hex, fsid_t *fsid);
 int	 sacmp (struct sockaddr *, struct sockaddr *);
 int	 umountall (char **);
 int	 checkname (char *, char **);
-int	 umountfs (char *, char *, fsid_t *, char *);
+int	 umountfs(struct statfs *sfs);
 void	 usage (void);
 int	 xdr_dir (XDR *, char *);
 
@@ -159,8 +157,7 @@ main(int argc, char *argv[])
 			sfs = &mntbuf[mntsize];
 			if (checkvfsname(sfs->f_fstypename, typelist))
 				continue;
-			if (umountfs(sfs->f_mntfromname, sfs->f_mntonname,
-			    &sfs->f_fsid, sfs->f_fstypename) != 0)
+			if (umountfs(sfs) != 0)
 				errs = 1;
 		}
 		free(mntbuf);
@@ -176,7 +173,6 @@ main(int argc, char *argv[])
 				errs = 1;
 		break;
 	}
-	(void)getmntentry(NULL, NULL, NOTHING, FREE);
 	exit(errs);
 }
 
@@ -230,21 +226,18 @@ umountall(char **typelist)
 }
 
 /*
- * Do magic checks on mountpoint and device or hand over
- * it to unmount(2) if everything fails.
+ * Do magic checks on mountpoint/device/fsid, and then call unmount(2).
  */
 int
 checkname(char *name, char **typelist)
 {
-	size_t len;
-	int speclen;
-	char *resolved, realname[MAXPATHLEN];
-	char *hostp, *delimp, *origname;
+	char buf[MAXPATHLEN];
+	struct statfs sfsbuf;
+	struct stat sb;
 	struct statfs *sfs;
-
-	len = 0;
-	delimp = hostp = NULL;
-	sfs = NULL;
+	char *delimp;
+	dev_t dev;
+	int len;
 
 	/*
 	 * 1. Check if the name exists in the mounttable.
@@ -255,108 +248,67 @@ checkname(char *name, char **typelist)
 	 * we look up the name in the mounttable again.
 	 */
 	if (sfs == NULL) {
-		speclen = strlen(name);
-		for (speclen = strlen(name); 
-		    speclen > 1 && name[speclen - 1] == '/';
-		    speclen--)
-			name[speclen - 1] = '\0';
+		len = strlen(name);
+		while (len > 0 && name[len - 1] == '/')
+			name[--len] = '\0';
 		sfs = checkmntlist(name);
-		resolved = name;
-		/* Save off original name in origname */
-		if ((origname = strdup(name)) == NULL)
-			err(1, "strdup");
-		/*
-		 * 3. Check if the deprecated nfs-syntax with an '@'
-		 * has been used and translate it to the ':' syntax.
-		 * Look up the name in the mounttable again.
-		 */
-		if (sfs == NULL) {
-			if ((delimp = strrchr(name, '@')) != NULL) {
-				hostp = delimp + 1;
-				if (*hostp != '\0') {
-					/*
-					 * Make both '@' and ':'
-					 * notations equal 
-					 */
-					char *host = strdup(hostp);
-					len = strlen(hostp);
-					if (host == NULL)
-						err(1, "strdup");
-					memmove(name + len + 1, name,
-					    (size_t)(delimp - name));
-					name[len] = ':';
-					memmove(name, host, len);
-					free(host);
-				}
-				for (speclen = strlen(name); 
-				    speclen > 1 && name[speclen - 1] == '/';
-				    speclen--)
-					name[speclen - 1] = '\0';
-				name[len + speclen + 1] = '\0';
-				sfs = checkmntlist(name);
-				resolved = name;
-			}
-			/*
-			 * 4. Check if a relative mountpoint has been
-			 * specified. This should happen as last check,
-			 * the order is important. To prevent possible
-			 * nfs-hangs, we just call realpath(3) on the
-			 * basedir of mountpoint and add the dirname again.
-			 * Check the name in mounttable one last time.
-			 */
-			if (sfs == NULL) {
-				(void)strcpy(name, origname);
-				if ((getrealname(name, realname)) != NULL) {
-					sfs = checkmntlist(realname);
-					resolved = realname;
-				}
-				/*
-				 * 5. All tests failed, just hand over the
-				 * mountpoint to the kernel, maybe the statfs
-				 * structure has been truncated or is not
-				 * useful anymore because of a chroot(2).
-				 * Please note that nfs will not be able to
-				 * notify the nfs-server about unmounting.
-				 * These things can change in future when the 
-				 * fstat structure get's more reliable,
-				 * but at the moment we cannot thrust it.
-				 */
-				if (sfs == NULL) {
-					(void)strcpy(name, origname);
-					if (umountfs(NULL, origname, NULL,
-					    "none") == 0) {;
-						warnx("%s not found in "
-						    "mount table, "
-						    "unmounted it anyway",
-						    origname);
-						free(origname);
-						return (0);
-					} else
-						free(origname);
-						return (1);
-				}
-			}
+	}
+	/*
+	 * 3. Check if the deprecated NFS syntax with an '@' has been used
+	 * and translate it to the ':' syntax. Look up the name in the
+	 * mount table again.
+	 */
+	if (sfs == NULL && (delimp = strrchr(name, '@')) != NULL) {
+		snprintf(buf, sizeof(buf), "%s:%.*s", delimp + 1, delimp - name,
+		    name);
+		len = strlen(buf);
+		while (len > 0 && buf[len - 1] == '/')
+			buf[--len] = '\0';
+		sfs = checkmntlist(buf);
+	}
+	/*
+	 * 4. Resort to a statfs(2) call. This is the last check so that
+	 * hung NFS filesystems for example can be unmounted without
+	 * potentially blocking forever in statfs() as long as the
+	 * filesystem is specified unambiguously. This covers all the
+	 * hard cases such as symlinks and mismatches between the
+	 * mount list and reality.
+	 * We also do this if an ambiguous mount point was specified.
+	 */
+	if (sfs == NULL || (getmntentry(NULL, name, NULL, FIND) != NULL &&
+	    getmntentry(NULL, name, NULL, CHECKUNIQUE) == NULL)) {
+		if (statfs(name, &sfsbuf) != 0) {
+			warn("%s: statfs", name);
+		} else if (stat(name, &sb) != 0) {
+			warn("%s: stat", name);
+		} else if (S_ISDIR(sb.st_mode)) {
+			/* Check that `name' is the root directory. */
+			dev = sb.st_dev;
+			snprintf(buf, sizeof(buf), "%s/..", name);
+			if (stat(buf, &sb) != 0) {
+				warn("%s: stat", buf);
+			} else if (sb.st_dev == dev) {
+				warnx("%s: not a file system root directory",
+				    name);
+				return (1);
+			} else
+				sfs = &sfsbuf;
 		}
-		free(origname);
-	} else
-		resolved = name;
-
+	}
+	if (sfs == NULL) {
+		warnx("%s: unknown file system", name);
+		return (1);
+	}
 	if (checkvfsname(sfs->f_fstypename, typelist))
 		return (1);
-
-	/*
-	 * Mark the uppermost mount as unmounted.
-	 */
-	(void)getmntentry(sfs->f_mntfromname, sfs->f_mntonname, NOTHING, MARK);
-	return (umountfs(sfs->f_mntfromname, sfs->f_mntonname, &sfs->f_fsid,
-	    sfs->f_fstypename));
+	return (umountfs(sfs));
 }
 
 /*
  * NFS stuff and unmount(2) call
  */
 int
-umountfs(char *mntfromname, char *mntonname, fsid_t *fsid, char *type)
+umountfs(struct statfs *sfs)
 {
 	char fsidbuf[64];
 	enum clnt_stat clnt_stat;
@@ -373,8 +325,8 @@ umountfs(char *mntfromname, char *mntonname, fsid_t *fsid, char *type)
 	nfsdirname = delimp = orignfsdirname = NULL;
 	memset(&hints, 0, sizeof hints);
 
-	if (strcmp(type, "nfs") == 0) {
-		if ((nfsdirname = strdup(mntfromname)) == NULL)
+	if (strcmp(sfs->f_fstypename, "nfs") == 0) {
+		if ((nfsdirname = strdup(sfs->f_mntfromname)) == NULL)
 			err(1, "strdup");
 		orignfsdirname = nfsdirname;
 		if ((delimp = strrchr(nfsdirname, ':')) != NULL) {
@@ -396,31 +348,32 @@ umountfs(char *mntfromname, char *mntonname, fsid_t *fsid, char *type)
 		 * A non-NULL return means that this is the last
 		 * mount from mntfromname that is still mounted.
 		 */
-		if (getmntentry(mntfromname, NULL, NOTHING, COUNT) != NULL)
+		if (getmntentry(sfs->f_mntfromname, NULL, NULL,
+		    CHECKUNIQUE) != NULL)
 			do_rpc = 1;
 	}
 
 	if (!namematch(ai))
 		return (1);
-	/* First try to unmount using the specified file system ID. */
-	if (fsid != NULL) {
-		snprintf(fsidbuf, sizeof(fsidbuf), "FSID:%d:%d", fsid->val[0],
-		    fsid->val[1]);
-		if (unmount(fsidbuf, fflag | MNT_BYFSID) != 0) {
-			warn("unmount of %s failed", mntonname);
-			if (errno != ENOENT)
-				return (1);
-			/* Compatability for old kernels. */
-			warnx("retrying using path instead of file system ID");
-			fsid = NULL;
+	/* First try to unmount using the file system ID. */
+	snprintf(fsidbuf, sizeof(fsidbuf), "FSID:%d:%d", sfs->f_fsid.val[0],
+	    sfs->f_fsid.val[1]);
+	if (unmount(fsidbuf, fflag | MNT_BYFSID) != 0) {
+		warn("unmount of %s failed", sfs->f_mntonname);
+		if (errno != ENOENT)
+			return (1);
+		/* Compatability for old kernels. */
+		warnx("retrying using path instead of file system ID");
+		if (unmount(sfs->f_mntonname, fflag) != 0) {
+			warn("unmount of %s failed", sfs->f_mntonname);
+			return (1);
 		}
 	}
-	if (fsid == NULL && unmount(mntonname, fflag) != 0) {
-		warn("unmount of %s failed", mntonname);
-		return (1);
-	}
+	/* Mark this this file system as unmounted. */
+	getmntentry(NULL, NULL, &sfs->f_fsid, REMOVE);
 	if (vflag)
-		(void)printf("%s: unmount from %s\n", mntfromname, mntonname);
+		(void)printf("%s: unmount from %s\n", sfs->f_mntfromname,
+		    sfs->f_mntonname);
 	/*
 	 * Report to mountd-server which nfsname
 	 * has been unmounted.
@@ -460,14 +413,12 @@ umountfs(char *mntfromname, char *mntonname, fsid_t *fsid, char *type)
 }
 
 struct statfs *
-getmntentry(const char *fromname, const char *onname, mntwhat what, dowhat mark)
+getmntentry(const char *fromname, const char *onname, fsid_t *fsid, dowhat what)
 {
 	static struct statfs *mntbuf;
 	static size_t mntsize = 0;
 	static char *mntcheck = NULL;
-	static char *mntcount = NULL;
-	fsid_t fsid;
-	char hexbuf[3];
+	struct statfs *sfs, *foundsfs;
 	int i, count;
 
 	if (mntsize <= 0) {
@@ -475,116 +426,46 @@ getmntentry(const char *fromname, const char *onname, mntwhat what, dowhat mark)
 			return (NULL);
 	}
 	if (mntcheck == NULL) {
-		if ((mntcheck = calloc(mntsize + 1, sizeof(int))) == NULL ||
-		    (mntcount = calloc(mntsize + 1, sizeof(int))) == NULL)
+		if ((mntcheck = calloc(mntsize + 1, sizeof(int))) == NULL)
 			err(1, "calloc");
 	}
 	/*
 	 * We want to get the file systems in the reverse order
-	 * that they were mounted. Mounted and unmounted file systems
-	 * are marked or unmarked in a table called 'mntcheck'.
-	 * Unmount(const char *dir, int flags) does only take the
-	 * mountpoint as argument, not the destination. If we don't pay
-	 * attention to the order, it can happen that an overlaying
-	 * file system gets unmounted instead of the one the user
-	 * has choosen.
+	 * that they were mounted. Unmounted file systems are marked
+	 * in a table called 'mntcheck'.
 	 */
-	switch (mark) {
-	case NAME:
-		/* Return only the specific name */
-		if (fromname == NULL)
-			return (NULL);
-		if (what == MNTFSID) {
-			/* Convert the hex filesystem ID to a fsid_t. */
-			if (strlen(fromname) != sizeof(fsid) * 2)
-				return (NULL);
-			hexbuf[2] = '\0';
-			for (i = 0; i < sizeof(fsid); i++) {
-				hexbuf[0] = fromname[i * 2];
-				hexbuf[1] = fromname[i * 2 + 1];
-				if (!isxdigit(hexbuf[0]) ||
-				    !isxdigit(hexbuf[1]))
-					return (NULL);
-				((u_char *)&fsid)[i] = strtol(hexbuf, NULL, 16);
-			}
-		}
-		for (i = mntsize - 1; i >= 0; i--) {
-			switch (what) {
-			case MNTON:
-				if (strcmp(mntbuf[i].f_mntonname,
-				    fromname) != 0)
-					continue;
-				break;
-			case MNTFROM:
-				if (strcmp(mntbuf[i].f_mntfromname,
-				    fromname) != 0)
-					continue;
-			case MNTFSID:
-				if (bcmp(&mntbuf[i].f_fsid, &fsid,
-				    sizeof(fsid)) != 0)
-				continue;
-			case NOTHING: /* silence compiler warning */
-				break;
-			}
-			if (mntcheck[i] != 1)
-				return (&mntbuf[i]);
-		}
+	count = 0;
+	foundsfs = NULL;
+	for (i = mntsize - 1; i >= 0; i--) {
+		if (mntcheck[i])
+			continue;
+		sfs = &mntbuf[i];
+		if (fromname != NULL && strcmp(sfs->f_mntfromname,
+		    fromname) != 0)
+			continue;
+		if (onname != NULL && strcmp(sfs->f_mntonname, onname) != 0)
+			continue;
+		if (fsid != NULL && bcmp(&sfs->f_fsid, fsid,
+		    sizeof(*fsid)) != 0)
+			continue;
 
-		return (NULL);
-	case MARK:
-		/* Mark current mount with '1' and return name */
-		for (i = mntsize - 1; i >= 0; i--) {
-			if (mntcheck[i] == 0 &&
-			    (strcmp(mntbuf[i].f_mntonname, onname) == 0) &&
-			    (strcmp(mntbuf[i].f_mntfromname, fromname) == 0)) {
-				mntcheck[i] = 1;
-				return (&mntbuf[i]);
-			}
-		}
-		return (NULL);
-	case UNMARK:
-		/* Unmark current mount with '0' and return name */
-		for (i = 0; i < mntsize; i++) {
-			if (mntcheck[i] == 1 &&
-			    (strcmp(mntbuf[i].f_mntonname, onname) == 0) &&
-			    (strcmp(mntbuf[i].f_mntfromname, fromname) == 0)) {
-				mntcheck[i] = 0;
-				return (&mntbuf[i]);
-			}
-		}
-		return (NULL);
-	case COUNT:
-		/* Count the equal mntfromnames */
-		count = 0;
-		for (i = mntsize - 1; i >= 0; i--) {
-			if (strcmp(mntbuf[i].f_mntfromname, fromname) == 0)
-				count++;
-		}
-		/* Mark the already unmounted mounts and return
-		 * mntfromname if count <= 1. Else return NULL.
-		 */
-		for (i = mntsize - 1; i >= 0; i--) {
-			if (strcmp(mntbuf[i].f_mntfromname, fromname) == 0) {
-				if (mntcount[i] == 1)
-					count--;
-				else {
-					mntcount[i] = 1;
-					break;
-				}
-			}
+		switch (what) {
+		case CHECKUNIQUE:
+			foundsfs = sfs;
+			count++;
+			continue;
+		case REMOVE:
+			mntcheck[i] = 1;
+			break;
+		default:
+			break;
 		}
-		if (count <= 1)
-			return (&mntbuf[i]);
-		else
-			return (NULL);
-	case FREE:
-		free(mntbuf);
-		free(mntcheck);
-		free(mntcount);
-		return (NULL);
-	default:
-		return (NULL);
+		return (sfs);
 	}
+
+	if (what == CHECKUNIQUE && count == 1)
+		return (foundsfs);
+	return (NULL);
 }
 
 int
@@ -642,12 +523,15 @@ struct statfs *
 checkmntlist(char *name)
 {
 	struct statfs *sfs;
+	fsid_t fsid;
 
-	sfs = getmntentry(name, NULL, MNTFSID, NAME);
+	sfs = NULL;
+	if (parsehexfsid(name, &fsid) == 0)
+		sfs = getmntentry(NULL, NULL, &fsid, FIND);
 	if (sfs == NULL)
-		sfs = getmntentry(name, NULL, MNTON, NAME);
+		sfs = getmntentry(NULL, name, NULL, FIND);
 	if (sfs == NULL)
-		sfs = getmntentry(name, NULL, MNTFROM, NAME);
+		sfs = getmntentry(name, NULL, NULL, FIND);
 	return (sfs);
 }
 
@@ -669,65 +553,27 @@ mntinfo(struct statfs **mntbuf)
 	return (mntsize);
 }
 
-char *
-getrealname(char *name, char *realname)
+/*
+ * Convert a hexidecimal filesystem ID to an fsid_t.
+ * Returns 0 on success.
+ */
+int
+parsehexfsid(const char *hex, fsid_t *fsid)
 {
-	char *dirname;
-	int havedir;
-	size_t baselen;
-	size_t dirlen;
-	
-	dirname = '\0';
-	havedir = 0;
-	if (*name == '/') {
-		if (ISDOT(name + 1) || ISDOTDOT(name + 1))
-			strcpy(realname, "/");
-		else {
-			if ((dirname = strrchr(name + 1, '/')) == NULL)
-				snprintf(realname, MAXPATHLEN, "%s", name);
-			else
-				havedir = 1;
-		}
-	} else {
-		if (ISDOT(name) || ISDOTDOT(name))
-			(void)realpath(name, realname);
-		else {
-			if ((dirname = strrchr(name, '/')) == NULL) {
-				if ((realpath(name, realname)) == NULL)
-					return (NULL);
-			} else 
-				havedir = 1;
-		}
-	}
-	if (havedir) {
-		*dirname++ = '\0';
-		if (ISDOT(dirname)) {
-			*dirname = '\0';
-			if ((realpath(name, realname)) == NULL)
-				return (NULL);
-		} else if (ISDOTDOT(dirname)) {
-			*--dirname = '/';
-			if ((realpath(name, realname)) == NULL)
-				return (NULL);
-		} else {
-			if ((realpath(name, realname)) == NULL)
-				return (NULL);
-			baselen = strlen(realname);
-			dirlen = strlen(dirname);
-			if (baselen + dirlen + 1 > MAXPATHLEN)
-				return (NULL);
-			if (realname[1] == '\0') {
-				memmove(realname + 1, dirname, dirlen);
-				realname[dirlen + 1] = '\0';
-			} else {
-				realname[baselen] = '/';
-				memmove(realname + baselen + 1,
-				    dirname, dirlen);
-				realname[baselen + dirlen + 1] = '\0';
-			}
-		}
+	char hexbuf[3];
+	int i;
+
+	if (strlen(hex) != sizeof(*fsid) * 2)
+		return (-1);
+	hexbuf[2] = '\0';
+	for (i = 0; i < sizeof(*fsid); i++) {
+		hexbuf[0] = hex[i * 2];
+		hexbuf[1] = hex[i * 2 + 1];
+		if (!isxdigit(hexbuf[0]) || !isxdigit(hexbuf[1]))
+			return (-1);
+		((u_char *)fsid)[i] = strtol(hexbuf, NULL, 16);
 	}
-	return (realname);
+	return (0);
 }
 
 /*