3 files changed, 108 insertions, 1 deletions
diff --git a/hw/9pfs/9p-util.c b/hw/9pfs/9p-util.c
new file mode 100644
index 0000000000..54134b0bb4
--- /dev/null
+++ b/hw/9pfs/9p-util.c
@@ -0,0 +1,57 @@
+/*
+ * 9p utilities
+ *
+ * Copyright IBM, Corp. 2017
+ *
+ * Authors:
+ *  Greg Kurz <groug@kaod.org>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "9p-util.h"
+
+int relative_openat_nofollow(int dirfd, const char *path, int flags,
+                             mode_t mode)
+{
+    int fd;
+
+    fd = dup(dirfd);
+    if (fd == -1) {
+        return -1;
+    }
+
+    while (*path) {
+        const char *c;
+        int next_fd;
+        char *head;
+
+        /* Only relative paths without consecutive slashes */
+        assert(path[0] != '/');
+
+        head = g_strdup(path);
+        c = strchr(path, '/');
+        if (c) {
+            head[c - path] = 0;
+            next_fd = openat_dir(fd, head);
+        } else {
+            next_fd = openat_file(fd, head, flags, mode);
+        }
+        g_free(head);
+        if (next_fd == -1) {
+            close_preserve_errno(fd);
+            return -1;
+        }
+        close(fd);
+        fd = next_fd;
+
+        if (!c) {
+            break;
+        }
+        path = c + 1;
+    }
+
+    return fd;
+}
diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h
new file mode 100644
index 0000000000..e80b5a551d
--- /dev/null
+++ b/hw/9pfs/9p-util.h
@@ -0,0 +1,50 @@
+/*
+ * 9p utilities
+ *
+ * Copyright IBM, Corp. 2017
+ *
+ * Authors:
+ *  Greg Kurz <groug@kaod.org>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef QEMU_9P_UTIL_H
+#define QEMU_9P_UTIL_H
+
+static inline void close_preserve_errno(int fd)
+{
+    int serrno = errno;
+    close(fd);
+    errno = serrno;
+}
+
+static inline int openat_dir(int dirfd, const char *name)
+{
+    return openat(dirfd, name, O_DIRECTORY | O_RDONLY | O_PATH);
+}
+
+static inline int openat_file(int dirfd, const char *name, int flags,
+                              mode_t mode)
+{
+    int fd, serrno, ret;
+
+    fd = openat(dirfd, name, flags | O_NOFOLLOW | O_NOCTTY | O_NONBLOCK,
+                mode);
+    if (fd == -1) {
+        return -1;
+    }
+
+    serrno = errno;
+    /* O_NONBLOCK was only needed to open the file. Let's drop it. */
+    ret = fcntl(fd, F_SETFL, flags);
+    assert(!ret);
+    errno = serrno;
+    return fd;
+}
+
+int relative_openat_nofollow(int dirfd, const char *path, int flags,
+                             mode_t mode);
+
+#endif
diff --git a/hw/9pfs/Makefile.objs b/hw/9pfs/Makefile.objs
index da0ae0cfdb..32197e6671 100644
--- a/hw/9pfs/Makefile.objs
+++ b/hw/9pfs/Makefile.objs
@@ -1,4 +1,4 @@
-common-obj-y  = 9p.o
+common-obj-y  = 9p.o 9p-util.o
 common-obj-y += 9p-local.o 9p-xattr.o
 common-obj-y += 9p-xattr-user.o 9p-posix-acl.o
 common-obj-y += coth.o cofs.o codir.o cofile.o