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[Qemu-devel] [PATCH v2 06/28] 9pfs: local: open/opendir: don't follow sy
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PATCH v2 06/28] 9pfs: local: open/opendir: don't follow symlinks |
Date: |
Sun, 26 Feb 2017 23:42:18 +0100 |
User-agent: |
StGit/0.17.1-20-gc0b1b-dirty |
The local_open() and local_opendir() callbacks are vulnerable to symlink
attacks because they call:
(1) open(O_NOFOLLOW) which follows symbolic links in all path elements but
the rightmost one
(2) opendir() which follows symbolic links in all path elements
This patch converts both callbacks to use new helpers based on
openat_nofollow() to only open files and directories if they are
below the virtfs shared folder
This partly fixes CVE-2016-9602.
Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
---
v2: - use LocalData type
- strip leading '/' characters in local_open_nofollow()
---
hw/9pfs/9p-local.c | 37 +++++++++++++++++++++++++++----------
hw/9pfs/9p-local.h | 20 ++++++++++++++++++++
2 files changed, 47 insertions(+), 10 deletions(-)
create mode 100644 hw/9pfs/9p-local.h
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index be6be615149b..74b921e65316 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -13,6 +13,7 @@
#include "qemu/osdep.h"
#include "9p.h"
+#include "9p-local.h"
#include "9p-xattr.h"
#include "9p-util.h"
#include "fsdev/qemu-fsdev.h" /* local_ops */
@@ -48,6 +49,24 @@ typedef struct {
int mountfd;
} LocalData;
+int local_open_nofollow(FsContext *fs_ctx, const char *path, int flags,
+ mode_t mode)
+{
+ LocalData *data = fs_ctx->private;
+
+ /* All paths are relative to the path data->mountfd points to */
+ while (*path == '/') {
+ path++;
+ }
+
+ return openat_nofollow(data->mountfd, path, flags, mode);
+}
+
+int local_opendir_nofollow(FsContext *fs_ctx, const char *path)
+{
+ return local_open_nofollow(fs_ctx, path, O_DIRECTORY | O_RDONLY, 0);
+}
+
#define VIRTFS_META_DIR ".virtfs_metadata"
static char *local_mapped_attr_path(FsContext *ctx, const char *path)
@@ -359,13 +378,9 @@ static int local_closedir(FsContext *ctx, V9fsFidOpenState
*fs)
static int local_open(FsContext *ctx, V9fsPath *fs_path,
int flags, V9fsFidOpenState *fs)
{
- char *buffer;
- char *path = fs_path->data;
int fd;
- buffer = rpath(ctx, path);
- fd = open(buffer, flags | O_NOFOLLOW);
- g_free(buffer);
+ fd = local_open_nofollow(ctx, fs_path->data, flags, 0);
if (fd == -1) {
return -1;
}
@@ -376,13 +391,15 @@ static int local_open(FsContext *ctx, V9fsPath *fs_path,
static int local_opendir(FsContext *ctx,
V9fsPath *fs_path, V9fsFidOpenState *fs)
{
- char *buffer;
- char *path = fs_path->data;
+ int dirfd;
DIR *stream;
- buffer = rpath(ctx, path);
- stream = opendir(buffer);
- g_free(buffer);
+ dirfd = local_opendir_nofollow(ctx, fs_path->data);
+ if (dirfd == -1) {
+ return -1;
+ }
+
+ stream = fdopendir(dirfd);
if (!stream) {
return -1;
}
diff --git a/hw/9pfs/9p-local.h b/hw/9pfs/9p-local.h
new file mode 100644
index 000000000000..32c72749d9df
--- /dev/null
+++ b/hw/9pfs/9p-local.h
@@ -0,0 +1,20 @@
+/*
+ * 9p local backend utilities
+ *
+ * Copyright IBM, Corp. 2017
+ *
+ * Authors:
+ * Greg Kurz <address@hidden>
+ *
+ * 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_LOCAL_H
+#define QEMU_9P_LOCAL_H
+
+int local_open_nofollow(FsContext *fs_ctx, const char *path, int flags,
+ mode_t mode);
+int local_opendir_nofollow(FsContext *fs_ctx, const char *path);
+
+#endif
- [Qemu-devel] [PATCH v2 00/28] Series short description, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 01/28] 9pfs: local: move xattr security ops to 9p-xattr.c, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 02/28] 9pfs: remove side-effects in local_init(), Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 03/28] 9pfs: remove side-effects in local_open() and local_opendir(), Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 04/28] 9pfs: introduce openat_nofollow() helper, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 05/28] 9pfs: local: keep a file descriptor on the shared folder, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 06/28] 9pfs: local: open/opendir: don't follow symlinks,
Greg Kurz <=
- [Qemu-devel] [PATCH v2 07/28] 9pfs: local: lgetxattr: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 08/28] 9pfs: local: llistxattr: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 09/28] 9pfs: local: lsetxattr: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 10/28] 9pfs: local: lremovexattr: don't follow symlinks, Greg Kurz, 2017/02/26