libmount: add umount(2) support

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 529 insertions, 0 deletions

diff --git a/shlibs/mount/src/context_umount.c b/shlibs/mount/src/context_umount.c
new file mode 100644
index 000000000..1222fe6f9
--- /dev/null
+++ b/shlibs/mount/src/context_umount.c
@@ -0,0 +1,529 @@
+/*
+ * Copyright (C) 2010 Karel Zak <kzak@redhat.com>
+ *
+ * This file may be redistributed under the terms of the
+ * GNU Lesser General Public License.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+#include <sys/wait.h>
+#include <sys/mount.h>
+
+#include "c.h"
+#include "pathnames.h"
+#include "strutils.h"
+#include "mountP.h"
+
+static int lookup_umount_fs(mnt_context *cxt)
+{
+	int rc;
+	const char *tgt;
+	mnt_tab *mtab;
+	mnt_fs *fs;
+
+	tgt = mnt_fs_get_target(cxt->fs);
+	if (!tgt) {
+		DBG(CXT, mnt_debug_h(cxt, "umount: undefined target"));
+		return -EINVAL;
+	}
+	rc = mnt_context_get_mtab(cxt, &mtab);
+	if (rc) {
+		DBG(CXT, mnt_debug_h(cxt, "umount: failed to read mtab"));
+		return rc;
+	}
+	fs = mnt_tab_find_target(mtab, tgt, MNT_ITER_BACKWARD);
+	if (!fs) {
+		/* maybe the option is source rather than target (mountpoint) */
+		fs = mnt_tab_find_source(mtab, tgt, MNT_ITER_BACKWARD);
+
+		if (fs) {
+			mnt_fs *fs1 = mnt_tab_find_target(mtab,
+							mnt_fs_get_target(fs),
+							MNT_ITER_BACKWARD);
+			if (!fs1) {
+				DBG(CXT, mnt_debug_h(cxt, "mtab is broken?!?!"));
+				return -EINVAL;
+			}
+			if (fs != fs1) {
+				/* Something was stacked over `file' on the
+				 * same mount point. */
+				DBG(CXT, mnt_debug_h(cxt,
+						"umount: %s: %s is mounted "
+						"over it on the same point",
+						tgt, mnt_fs_get_source(fs1)));
+				return -EINVAL;
+			}
+		}
+	}
+
+	if (!fs) {
+		DBG(CXT, mnt_debug_h(cxt, "cannot found %s in mtab", tgt));
+		return 0;
+	}
+
+	/* copy from mtab/fstab to our FS description
+	 */
+	rc = mnt_fs_set_source(cxt->fs, mnt_fs_get_source(fs));
+	if (!rc)
+		rc = mnt_fs_set_target(cxt->fs, mnt_fs_get_target(fs));
+
+	if (!rc && !mnt_fs_get_fstype(cxt->fs))
+		rc = mnt_fs_set_fstype(cxt->fs, mnt_fs_get_fstype(fs));
+	if (!rc)
+		rc = mnt_fs_set_optstr(cxt->fs, mnt_fs_get_optstr(fs));
+
+	cxt->flags |= MNT_FL_TAB_APPLIED;
+	return rc;
+}
+
+/* check if @devname is loopdev and if the device is associated
+ * with a source from @fstab_fs
+ *
+ * TODO : move this to loopdev.c
+ */
+static int mnt_loopdev_associated_fs(const char *devname, mnt_fs *fs)
+{
+	uintmax_t offset = 0;
+	const char *src;
+	char *val, *optstr;
+	size_t valsz;
+
+	/* check if it begins with /dev/loop */
+	if (strncmp(devname, _PATH_DEV_LOOP, sizeof(_PATH_DEV_LOOP)))
+		return 0;
+
+	src = mnt_fs_get_srcpath(fs);
+	if (!src)
+		return 0;
+
+	/* check for offset option in @fs */
+	optstr = (char *) mnt_fs_get_optstr(fs);
+	if (optstr && !mnt_optstr_get_option(optstr, "offset=", &val, &valsz)) {
+		int rc;
+
+		val = strndup(val, valsz);
+		if (!val)
+			return 0;
+		rc = strtosize(val, &offset);
+		free(val);
+		if (rc)
+			return 0;
+	}
+
+	/* TODO:
+	 * if (mnt_loopdev_associated_file(devname, src, offset))
+	 *	return 1;
+	 */
+	return 0;
+}
+
+/*
+ * Note that cxt->fs contains relevant mtab entry!
+ */
+static int evaluate_permissions(mnt_context *cxt)
+{
+	mnt_tab *fstab;
+	unsigned long u_flags;
+	const char *tgt, *src, *optstr;
+	int rc, ok = 0;
+	mnt_fs *fs;
+
+	if (!cxt || !cxt->fs)
+		return -EINVAL;
+
+	if (!mnt_context_is_restricted(cxt))
+		 return 0;		/* superuser mount */
+
+	if (!(cxt->flags & MNT_FL_TAB_APPLIED)) {
+		DBG(CXT, mnt_debug_h(cxt,
+				"cannot found %s in mtab and you are not root",
+				mnt_fs_get_target(cxt->fs)));
+		goto eperm;
+	}
+
+	mnt_context_get_userspace_mountflags(cxt, &u_flags);
+
+	if (!(cxt->flags & MNT_FL_NOHELPERS) && (u_flags & MNT_MS_UHELPER)) {
+		char *suffix = NULL;
+		char *o = (char *) mnt_fs_get_optstr(cxt->fs);
+		size_t valsz;
+
+		rc = mnt_optstr_get_option(o, "uhelper", &suffix, &valsz);
+		if (!rc) {
+			suffix = strndup(suffix, valsz);
+			if (!suffix)
+				return -ENOMEM;
+			rc = mnt_context_prepare_helper(cxt, "umount", suffix);
+		}
+		if (rc < 0)
+			return rc;
+		if (cxt->helper)
+			return 0;	/* we'll call /sbin/umount.<uhelper> */
+	}
+
+	/*
+	 * User mounts has to be in /etc/fstab
+	 */
+	rc = mnt_context_get_fstab(cxt, &fstab);
+	if (rc)
+		return rc;
+
+	tgt = mnt_fs_get_target(cxt->fs);
+	src = mnt_fs_get_source(cxt->fs);
+
+	/* If fstab contains the two lines
+	 *	/dev/sda1 /mnt/zip auto user,noauto  0 0
+	 *	/dev/sda4 /mnt/zip auto user,noauto  0 0
+	 * then "mount /dev/sda4" followed by "umount /mnt/zip" used to fail.
+	 * So, we must not look for file, but for the pair (dev,file) in fstab.
+	  */
+	fs = mnt_tab_find_pair(fstab, src, tgt, MNT_ITER_FORWARD);
+	if (!fs) {
+		/*
+		 * It's possible that there is /path/file.img in fstab and
+		 * /dev/loop0 in mtab -- then we have to check releation
+		 * between loopdev and the file.
+		 */
+		fs = mnt_tab_find_target(fstab, tgt, MNT_ITER_FORWARD);
+		if (fs) {
+			const char *dev = mnt_fs_get_srcpath(cxt->fs);		/* devname from mtab */
+
+			if (!dev || !mnt_loopdev_associated_fs(dev, fs))
+				fs = NULL;
+		}
+		if (!fs) {
+			DBG(CXT, mnt_debug_h(cxt,
+					"umount %s: mtab disagrees with fstab",
+					tgt));
+			goto eperm;
+		}
+	}
+
+	/*
+	 * User mounting and unmounting is allowed only if fstab contains one
+	 * of the options `user', `users' or `owner' or `group'.
+	 *
+	 * The option `users' allows arbitrary users to mount and unmount -
+	 * this may be a security risk.
+	 *
+	 * The options `user', `owner' and `group' only allow unmounting by the
+	 * user that mounted (visible in mtab).
+	 */
+	optstr = mnt_fs_get_optstr(fs);
+	if (!optstr)
+		goto eperm;
+
+	if (mnt_optstr_get_userspace_mountflags(optstr, &u_flags))
+		goto eperm;
+
+	if (u_flags & MNT_MS_USERS)
+		/* promiscuous setting in fstab */
+		return 0;
+	/*
+	 * Check user=<username> setting from mtab if there is user, owner or
+	 * group option in /etc/fstab
+	 */
+	if ((u_flags & MNT_MS_USER) || (u_flags & MNT_MS_OWNER) ||
+	    (u_flags & MNT_MS_GROUP)) {
+
+		char *curr_user = mnt_get_username(getuid());
+		char *mtab_user = NULL;
+		size_t sz;
+
+		if (!curr_user) {
+			DBG(CXT, mnt_debug_h(cxt, "umount %s: cannot "
+					"convert %d to username",
+					tgt, getuid()));
+			goto eperm;
+		}
+
+		/* get options from mtab */
+		optstr = mnt_fs_get_optstr(cxt->fs);
+		if (optstr && !mnt_optstr_get_option((char *) optstr,
+					"user", &mtab_user, &sz) && sz)
+			ok = !strncmp(curr_user, mtab_user, sz);
+	}
+
+	if (ok) {
+		DBG(CXT, mnt_debug_h(cxt, "umount %s is allowed", tgt));
+		return 0;
+	}
+eperm:
+	DBG(CXT, mnt_debug_h(cxt, "umount %s is not allowed for you", tgt));
+	return -EPERM;
+}
+
+static int exec_helper(mnt_context *cxt)
+{
+	int rc;
+
+	assert(cxt);
+	assert(cxt->fs);
+	assert(cxt->helper);
+
+	DBG_FLUSH;
+
+	switch (fork()) {
+	case 0:
+	{
+		const char *args[10], *type;
+		int i = 0;
+
+		if (setgid(getgid()) < 0)
+			exit(EXIT_FAILURE);
+
+		if (setuid(getuid()) < 0)
+			exit(EXIT_FAILURE);
+
+		type = mnt_fs_get_fstype(cxt->fs);
+
+		args[i++] = cxt->helper;			/* 1 */
+		args[i++] = mnt_fs_get_target(cxt->fs);		/* 2 */
+
+		if (cxt->flags & MNT_FL_NOMTAB)
+			args[i++] = "-n";			/* 3 */
+		if (cxt->flags & MNT_FL_LAZY)
+			args[i++] = "-l";			/* 4 */
+		if (cxt->flags & MNT_FL_FORCE)
+			args[i++] = "-f";			/* 5 */
+		if (cxt->flags & MNT_FL_VERBOSE)
+			args[i++] = "-v";			/* 6 */
+		if (cxt->flags & MNT_FL_RDONLY_UMOUNT)
+			args[i++] = "-r";			/* 7 */
+		if (type && !endswith(cxt->helper, type)) {
+			args[i++] = "-t";			/* 8 */
+			args[i++] = (char *) type;	/* 9 */
+		}
+
+		args[i] = NULL;					/* 10 */
+#ifdef CONFIG_LIBMOUNT_DEBUG
+		i = 0;
+		for (i = 0; args[i]; i++)
+			DBG(CXT, mnt_debug_h(cxt, "argv[%d] = \"%s\"",
+							i, args[i]));
+#endif
+		DBG_FLUSH;
+		execv(cxt->helper, (char * const *) args);
+		exit(EXIT_FAILURE);
+	}
+	default:
+	{
+		int st;
+		wait(&st);
+		cxt->helper_status = WIFEXITED(st) ? WEXITSTATUS(st) : -1;
+
+		DBG(CXT, mnt_debug_h(cxt, "%s executed [status=%d]",
+					cxt->helper, cxt->helper_status));
+		rc = 0;
+		break;
+	}
+
+	case -1:
+		rc = -errno;
+		DBG(CXT, mnt_debug_h(cxt, "fork() failed"));
+		break;
+	}
+
+	return rc;
+}
+
+static int do_umount(mnt_context *cxt)
+{
+	int rc = 0;
+	const char *src, *target;
+
+	assert(cxt);
+	assert(cxt->fs);
+
+	if (cxt->helper)
+		return exec_helper(cxt);
+
+	src = mnt_fs_get_srcpath(cxt->fs);
+	target = mnt_fs_get_target(cxt->fs);
+
+	if (!target)
+		return -EINVAL;
+
+	if (cxt->flags & MNT_FL_FAKE)
+		return 0;
+
+	if (cxt->flags & MNT_FL_LAZY)
+		rc = umount2(target, MNT_DETACH);
+
+	else if (cxt->flags & MNT_FL_FORCE) {
+		rc = umount2(target, MNT_FORCE);
+
+		if (rc < 0 && errno == ENOSYS)
+			rc = umount(target);
+	} else
+		rc = umount(target);
+
+	if (rc < 0)
+		cxt->syscall_errno = errno;
+
+	/*
+	 * try remount read-only
+	 */
+	if (rc < 0 && cxt->syscall_errno == EBUSY &&
+	    (cxt->flags & MNT_FL_RDONLY_UMOUNT) && src) {
+
+		cxt->mountflags |= MS_REMOUNT | MS_RDONLY;
+		cxt->flags &= ~MNT_FL_LOOPDEL;
+		DBG(CXT, mnt_debug_h(cxt, "umount(2) failed [errno=%d] -- "
+					"tring remount read-only",
+					cxt->syscall_errno));
+
+		rc = mount(src, target, NULL,
+			    MS_MGC_VAL | MS_REMOUNT | MS_RDONLY, NULL);
+		if (rc < 0) {
+			cxt->syscall_errno = errno;
+			DBG(CXT, mnt_debug_h(cxt, "read-only re-mount(2) failed "
+					"[errno=%d]",
+					cxt->syscall_errno));
+			return -cxt->syscall_errno;
+		}
+		cxt->syscall_errno = 0;
+		DBG(CXT, mnt_debug_h(cxt, "read-only re-mount(2) success"));
+		return 0;
+	}
+
+	if (rc < 0) {
+		DBG(CXT, mnt_debug_h(cxt, "umount(2) failed [errno=%d]",
+					cxt->syscall_errno));
+		return -cxt->syscall_errno;
+	}
+	DBG(CXT, mnt_debug_h(cxt, "umount(2) success"));
+	return 0;
+}
+
+/**
+ * mnt_context_prepare_umount:
+ * @cxt: mount context
+ *
+ * This function:
+ *	- read information from fstab/mtab (if necessary)
+ *	- check premissions
+ *	- prepare for mtab update (if necessary)
+ *
+ * It's strongly recommended to use this function before mnt_context_do_umount().
+ *
+ * Returns: 0 on success, and negative number in case of error.
+ */
+int mnt_context_prepare_umount(mnt_context *cxt)
+{
+	int rc = 0;
+
+	if (!cxt)
+		return -EINVAL;
+
+	if (!cxt->fs || (!mnt_fs_get_source(cxt->fs) &&
+			 !mnt_fs_get_target(cxt->fs)))
+		return -EINVAL;
+
+	free(cxt->helper);	/* be paranoid */
+	cxt->helper = NULL;
+
+	rc = lookup_umount_fs(cxt);
+	if (!rc)
+		rc = evaluate_permissions(cxt);
+	if (!rc && !cxt->helper)
+		rc = mnt_context_prepare_helper(cxt, "umount", NULL);
+/* TODO
+	if ((cxt->flags & MNT_FL_LOOPDEL) &&
+	    (!mnt_is_loopdev(src) || mnt_loopdev_is_autoclear(src)))
+		cxt->flags &= ~MNT_FL_LOOPDEL;
+*/
+	if (!rc)
+		rc = mnt_context_prepare_update(cxt, MNT_ACT_UMOUNT);
+	if (!rc) {
+		DBG(CXT, mnt_debug_h(cxt, "umount sucessfully prepared"));
+		return 0;
+	}
+
+	DBG(CXT, mnt_debug_h(cxt, "umount prepare failed"));
+	return rc;
+}
+
+/**
+ * mnt_context_do_umount:
+ * @cxt: mount context
+ *
+ * Umount filesystem by umount(2) or fork()+exec(/sbin/umount.<type>).
+ *
+ * See also mnt_context_disable_helpers().
+ *
+ * Returns: 0 on success, and negative number in case of error.
+ */
+int mnt_context_do_umount(mnt_context *cxt)
+{
+	if (!cxt || !cxt->fs || (cxt->fs->flags & MNT_FS_SWAP))
+		return -EINVAL;
+
+	return do_umount(cxt);
+}
+
+/**
+ * mnt_context_post_umount:
+ * @cxt: mount context
+ *
+ * Updates mtab and detroy loopdev etc. This function should be always called after
+ * mnt_context_do_umount().
+ *
+ * Returns: 0 on success, and negative number in case of error.
+ */
+int mnt_context_post_umount(mnt_context *cxt)
+{
+	int rc = 0;
+
+	if (!cxt)
+		return -EINVAL;
+	if (cxt->syscall_errno || cxt->helper)
+		return 0;
+/* TODO
+	if (cxt->flags & MNT_FL_LOOPDEL)
+		rc = mnt_loopdev_clean(mnt_fs_get_source(cxt->fs));
+*/
+	if (cxt->flags & MNT_FL_NOMTAB)
+		return rc;
+
+	if ((cxt->flags & MNT_FL_RDONLY_UMOUNT) &&
+	    (cxt->mountflags & (MS_RDONLY | MS_REMOUNT))) {
+		/*
+		 * refresh update to handle remount to read-only
+		 */
+		rc = mnt_context_prepare_update(cxt, MNT_ACT_MOUNT);
+		if (rc)
+			return rc;
+	}
+
+	/*
+	 * Update /etc/mtab or /var/run/mount/mountinfo
+	 */
+	if (cxt->update && !mnt_update_is_pointless(cxt->update)) {
+		rc = mnt_update_file(cxt->update);
+		if (!rc)
+			return rc;
+	}
+	return rc;
+}
+
+/**
+ * mnt_context_umount_strerror
+ * @cxt: mount context
+ * @buf: buffer
+ * @bufsiz: size of the buffer
+ *
+ * Returns: 0 or negative number in case of error.
+ */
+int mnt_context_umount_strerror(mnt_context *cxt, char *buf, size_t bufsiz)
+{
+	/* TODO: based on cxt->syscall_errno or cxt->helper_status */
+	return 0;
+}