libmount: Support unmount FUSE mounts

FUSE mounts don't need an fstab entry to be unmounted.
This checks if a mount is a FUSE mount before checking for
the fstab entry, and if so returns success.

[kzak@redhat.com: - use libmount tools for mount options
                  - use namespace switches
                  - cleanup code

 The requirement is user=<username> or user_id=<uid> in /proc/self/mountinfo
 for fuse filesystem. The logic is the same as for user= mount options, but in
 this case it is not maintained by libmount in userspace, but by fuse FS in kernel.]

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

1 files changed, 81 insertions, 1 deletions

diff --git a/libmount/src/context_umount.c b/libmount/src/context_umount.c
index d72f5ccd0..03c55ff61 100644
--- a/libmount/src/context_umount.c
+++ b/libmount/src/context_umount.c
@@ -388,6 +388,75 @@ static int prepare_helper_from_options(struct libmnt_context *cxt,
 	return rc;
 }
 
+static int is_fuse_usermount(struct libmnt_context *cxt, int *errsv)
+{
+	struct libmnt_ns *ns_old;
+	const char *type = mnt_fs_get_fstype(cxt->fs);
+	const char *optstr;
+	char *user = NULL, *user_id = NULL, *curr_user = NULL;
+	size_t sz;
+	uid_t uid;
+	int ok = 0;
+
+	*errsv = 0;
+
+	if (!type)
+		return 0;
+
+	if (strcmp(type, "fuse") != 0 &&
+	    strcmp(type, "fuseblk") != 0 &&
+	    strncmp(type, "fuse.", 5) != 0 &&
+	    strncmp(type, "fuseblk.", 8) != 0)
+		return 0;
+
+	/* get user= or user_id= from mtab/mountinfo */
+	optstr = mnt_fs_get_user_options(cxt->fs);
+	if (!optstr)
+		return 0;
+
+	if (mnt_optstr_get_option(optstr, "user", &user, &sz) != 0 &&
+	    mnt_optstr_get_option(optstr, "user_id", &user_id, &sz) != 0)
+		return 0;
+
+	if (sz == 0 || (user == NULL && user_id == NULL))
+		return 0;
+
+	/* get current user */
+	ns_old = mnt_context_switch_origin_ns(cxt);
+	if (!ns_old) {
+		*errsv = -MNT_ERR_NAMESPACE;
+		return 0;
+	}
+
+	uid = getuid();
+	if (user)
+		curr_user = mnt_get_username(uid);
+
+	if (!mnt_context_switch_ns(cxt, ns_old)) {
+		*errsv = -MNT_ERR_NAMESPACE;
+		return 0;
+	}
+
+	if (user && !curr_user) {
+		DBG(CXT, ul_debugobj(cxt, "umount (fuse): cannot "
+				"convert %d to username", uid));
+		return 0;
+	}
+
+	if (user)
+		ok = strncmp(curr_user, user, sz) == 0;
+
+	else if (user_id) {
+		char uidstr[sizeof(stringify_value(ULONG_MAX))];
+		snprintf(uidstr, sizeof(uidstr), "%lu", (unsigned long) uid);
+
+		ok = strncmp(user_id, uidstr, sz) == 0;
+	}
+
+	free(curr_user);
+	return ok;
+}
+
 /*
  * Note that cxt->fs contains relevant mtab entry!
  */
@@ -396,7 +465,7 @@ static int evaluate_permissions(struct libmnt_context *cxt)
 	struct libmnt_table *fstab;
 	unsigned long u_flags = 0;
 	const char *tgt, *src, *optstr;
-	int rc, ok = 0;
+	int rc = 0, ok = 0;
 	struct libmnt_fs *fs;
 
 	assert(cxt);
@@ -425,6 +494,17 @@ static int evaluate_permissions(struct libmnt_context *cxt)
 	}
 
 	/*
+	 * Check if this is a fuse mount for the current user,
+	 * if so then unmounting is allowed
+	 */
+	if (is_fuse_usermount(cxt, &rc)) {
+		DBG(CXT, ul_debugobj(cxt, "fuse user mount, umount is allowed"));
+		return 0;
+	}
+	if (rc)
+		return rc;
+
+	/*
 	 * User mounts have to be in /etc/fstab
 	 */
 	rc = mnt_context_get_fstab(cxt, &fstab);