libmount: fix chdir to parent for restricted (user) umounts

Reported-by: Petr Uzel <petr.uzel@suse.cz>
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/libmount/src/utils.c b/libmount/src/utils.c
index f3a174ff1a7bd42fa9fec1049463a47a8cf25961..239e587fe439137bbc595a124b0b1fc46cc1fab3 100644 (file)
--- a/libmount/src/utils.c
+++ b/libmount/src/utils.c
@@ -80,34 +80,40 @@ static char *stripoff_last_component(char *path)
        if (!p)
                return NULL;
        *p = '\0';
-       return ++p;
+       return p + 1;
 }
 
-/* Note that the @target has to be absolute path (so at least "/")
+/*
+ * Note that the @target has to be absolute path (so at least "/").  The
+ * @filename returns allocated buffer with last path component, for example:
+ *
+ * mnt_chdir_to_parent("/mnt/test", &buf) ==> chdir("/mnt"), buf="test"
  */
 int mnt_chdir_to_parent(const char *target, char **filename)
 {
-       char *path, *last = NULL;
+       char *buf, *parent, *last = NULL;
        char cwd[PATH_MAX];
        int rc = -EINVAL;
 
        if (!target || *target != '/')
                return -EINVAL;
 
-       path = strdup(target);
-       if (!path)
+       DBG(UTILS, mnt_debug("moving to %s parent", target));
+
+       buf = strdup(target);
+       if (!buf)
                return -ENOMEM;
 
-       if (*(path + 1) != '\0') {
-               last = stripoff_last_component(path);
+       if (*(buf + 1) != '\0') {
+               last = stripoff_last_component(buf);
                if (!last)
                        goto err;
        }
-       if (!*path)
-               *path = '/';    /* root */
 
-       if (chdir(path) == -1) {
-               DBG(UTILS, mnt_debug("failed to chdir to %s: %m", path));
+       parent = buf && *buf ? buf : "/";
+
+       if (chdir(parent) == -1) {
+               DBG(UTILS, mnt_debug("failed to chdir to %s: %m", parent));
                rc = -errno;
                goto err;
        }
@@ -116,14 +122,17 @@ int mnt_chdir_to_parent(const char *target, char **filename)
                rc = -errno;
                goto err;
        }
-       if (strcmp(cwd, path) != 0) {
-               DBG(UTILS, mnt_debug("path moved (%s -> %s)", path, cwd));
+       if (strcmp(cwd, parent) != 0) {
+               DBG(UTILS, mnt_debug(
+                   "unexpected chdir (expected=%s, cwd=%s)", parent, cwd));
                goto err;
        }
 
-       DBG(CXT, mnt_debug("current directory moved to %s", path));
+       DBG(CXT, mnt_debug(
+               "current directory moved to %s [last_component='%s']",
+               parent, last));
 
-       *filename = path;
+       *filename = buf;
 
        if (!last || !*last)
                memcpy(*filename, ".", 2);
@@ -131,7 +140,7 @@ int mnt_chdir_to_parent(const char *target, char **filename)
                memcpy(*filename, last, strlen(last) + 1);
        return 0;
 err:
-       free(path);
+       free(buf);
        return rc;
 }