switch_root: use file descriptor instead of path for recursiveRemove()

This makes recursiveRemove() use fdopendir() instead of taking a path,
so we're always sure about which namespace we're starting from.

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

diff --git a/sys-utils/switch_root.c b/sys-utils/switch_root.c
index 8daacb1d0e85bdc0be77e680df7ad65048c4b75b..75725e707277ed08f3955b722246811a10f04c68 100644 (file)
--- a/sys-utils/switch_root.c
+++ b/sys-utils/switch_root.c
@@ -39,22 +39,23 @@
 #endif
 
 /* remove all files/directories below dirName -- don't cross mountpoints */
-static int recursiveRemove(char *dirName)
+static int recursiveRemove(int fd)
 {
        struct stat rb;
        DIR *dir;
        int rc = -1;
        int dfd;
 
-       if (!(dir = opendir(dirName))) {
-               warn("failed to open %s", dirName);
+       if (!(dir = fdopendir(fd))) {
+               warn("failed to open directory");
                goto done;
        }
 
+       /* fdopendir() precludes us from continuing to use the input fd */
        dfd = dirfd(dir);
 
        if (fstat(dfd, &rb)) {
-               warn("failed to stat %s", dirName);
+               warn("failed to stat directory");
                goto done;
        }
 
@@ -64,7 +65,7 @@ static int recursiveRemove(char *dirName)
                errno = 0;
                if (!(d = readdir(dir))) {
                        if (errno) {
-                               warn("failed to read %s", dirName);
+                               warn("failed to read directory");
                                goto done;
                        }
                        break;  /* end of directory */
@@ -77,24 +78,26 @@ static int recursiveRemove(char *dirName)
                        struct stat sb;
 
                        if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
-                               warn("failed to stat %s/%s", dirName, d->d_name);
+                               warn("failed to stat %s", d->d_name);
                                continue;
                        }
 
                        /* remove subdirectories if device is same as dir */
                        if (sb.st_dev == rb.st_dev) {
-                               char subdir[ strlen(dirName) +
-                                            strlen(d->d_name) + 2 ];
+                               int cfd;
 
-                               sprintf(subdir, "%s/%s", dirName, d->d_name);
-                               recursiveRemove(subdir);
+                               cfd = openat(dfd, d->d_name, O_RDONLY);
+                               if (cfd >= 0) {
+                                       recursiveRemove(cfd);
+                                       close(cfd);
+                               }
                        } else
                                continue;
                }
 
                if (unlinkat(dfd, d->d_name,
                             d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
-                       warn("failed to unlink %s/%s", dirName, d->d_name);
+                       warn("failed to unlink %s", d->d_name);
        }
 
        rc = 0; /* success */
@@ -110,6 +113,7 @@ static int switchroot(const char *newroot)
        /*  Don't try to unmount the old "/", there's no way to do it. */
        const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
        int i;
+       int cfd;
 
        for (i = 0; umounts[i] != NULL; i++) {
                char newmount[PATH_MAX];
@@ -129,7 +133,11 @@ static int switchroot(const char *newroot)
                return -1;
        }
 
-       recursiveRemove("/");
+       cfd = open("/", O_RDONLY);
+       if (cfd >= 0) {
+               recursiveRemove(cfd);
+               close(cfd);
+       }
 
        if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
                warn("failed to mount moving %s to /", newroot);