From a33eda0dd99e00faa3bacae43d19490bb9500e07 Mon Sep 17 00:00:00 2001 From: Greg Kurz 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 Reviewed-by: Stefan Hajnoczi --- 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 8fb79e44b5..a6dd77d7b8 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -959,13 +959,20 @@ 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; }