File 0171-9pfs-local-utimensat-don-t-follow-s.patch of Package qemu-linux-user.15026

From 2023ebc470427fb5156bb78171690acd8f003249 Mon Sep 17 00:00:00 2001
From: Greg Kurz <groug@kaod.org>
Date: Sun, 26 Feb 2017 23:43:17 +0100
Subject: [PATCH] 9pfs: local: utimensat: don't follow symlinks

The local_utimensat() callback is vulnerable to symlink attacks because it
calls qemu_utimens()->utimensat(AT_SYMLINK_NOFOLLOW) which follows symbolic
links in all path elements but the rightmost one or qemu_utimens()->utimes()
which follows symbolic links for all path elements.

This patch converts local_utimensat() to rely on opendir_nofollow() and
utimensat(AT_SYMLINK_NOFOLLOW) directly instead of using qemu_utimens().
It is hence assumed that the OS supports utimensat(), i.e. has glibc 2.6
or higher and linux 2.6.22 or higher, which seems reasonable nowadays.

This partly fixes CVE-2016-9602.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit a33eda0dd99e00faa3bacae43d19490bb9500e07)
[BR: Fix and/or infrastructure for BSC#1020427 CVE-2016-9602]
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 hw/9pfs/9p-local.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index d9c8d2c3bf..4b2720557a 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -958,13 +958,20 @@ static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
 static int local_utimensat(FsContext *s, V9fsPath *fs_path,
                            const struct timespec *buf)
 {
-    char *buffer;
-    int ret;
-    char *path = fs_path->data;
+    char *dirpath = g_path_get_dirname(fs_path->data);
+    char *name = g_path_get_basename(fs_path->data);
+    int dirfd, ret = -1;
 
-    buffer = rpath(s, path);
-    ret = qemu_utimens(buffer, buf);
-    g_free(buffer);
+    dirfd = local_opendir_nofollow(s, dirpath);
+    if (dirfd == -1) {
+        goto out;
+    }
+
+    ret = utimensat(dirfd, name, buf, AT_SYMLINK_NOFOLLOW);
+    close_preserve_errno(dirfd);
+out:
+    g_free(dirpath);
+    g_free(name);
     return ret;
 }