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[Qemu-devel] [PATCH v2 07/28] 9pfs: local: lgetxattr: don't follow symli
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PATCH v2 07/28] 9pfs: local: lgetxattr: don't follow symlinks |
Date: |
Sun, 26 Feb 2017 23:42:26 +0100 |
User-agent: |
StGit/0.17.1-20-gc0b1b-dirty |
The local_lgetxattr() callback is vulnerable to symlink attacks because
it calls lgetxattr() which follows symbolic links in all path elements but
the rightmost one.
This patch introduces a helper to emulate the non-existing fgetxattrat()
function: it is implemented with /proc/self/fd which provides a trusted
path that can be safely passed to lgetxattr().
local_lgetxattr() is converted to use this helper and opendir_nofollow().
This partly fixes CVE-2016-9602.
Signed-off-by: Greg Kurz <address@hidden>
---
v2: - introduce /proc based fgetxattrat_nofollow()
---
hw/9pfs/9p-posix-acl.c | 16 ++--------------
hw/9pfs/9p-util.c | 12 ++++++++++++
hw/9pfs/9p-util.h | 2 ++
hw/9pfs/9p-xattr-user.c | 8 +-------
hw/9pfs/9p-xattr.c | 31 ++++++++++++++++++++++++-------
hw/9pfs/9p-xattr.h | 2 ++
6 files changed, 43 insertions(+), 28 deletions(-)
diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c
index ec003181cd33..9435e27a368c 100644
--- a/hw/9pfs/9p-posix-acl.c
+++ b/hw/9pfs/9p-posix-acl.c
@@ -25,13 +25,7 @@
static ssize_t mp_pacl_getxattr(FsContext *ctx, const char *path,
const char *name, void *value, size_t size)
{
- char *buffer;
- ssize_t ret;
-
- buffer = rpath(ctx, path);
- ret = lgetxattr(buffer, MAP_ACL_ACCESS, value, size);
- g_free(buffer);
- return ret;
+ return local_getxattr_nofollow(ctx, path, MAP_ACL_ACCESS, value, size);
}
static ssize_t mp_pacl_listxattr(FsContext *ctx, const char *path,
@@ -89,13 +83,7 @@ static int mp_pacl_removexattr(FsContext *ctx,
static ssize_t mp_dacl_getxattr(FsContext *ctx, const char *path,
const char *name, void *value, size_t size)
{
- char *buffer;
- ssize_t ret;
-
- buffer = rpath(ctx, path);
- ret = lgetxattr(buffer, MAP_ACL_DEFAULT, value, size);
- g_free(buffer);
- return ret;
+ return local_getxattr_nofollow(ctx, path, MAP_ACL_DEFAULT, value, size);
}
static ssize_t mp_dacl_listxattr(FsContext *ctx, const char *path,
diff --git a/hw/9pfs/9p-util.c b/hw/9pfs/9p-util.c
index 62fd7a76212a..b3dd1f160280 100644
--- a/hw/9pfs/9p-util.c
+++ b/hw/9pfs/9p-util.c
@@ -11,6 +11,7 @@
*/
#include "qemu/osdep.h"
+#include "qemu/xattr.h"
#include "9p-util.h"
int openat_nofollow(int dirfd, const char *path, int flags, mode_t mode)
@@ -51,3 +52,14 @@ int openat_nofollow(int dirfd, const char *path, int flags,
mode_t mode)
return fd;
}
+
+ssize_t fgetxattrat_nofollow(int dirfd, const char *filename, const char *name,
+ void *value, size_t size)
+{
+ char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename);
+ int ret;
+
+ ret = lgetxattr(proc_path, name, value, size);
+ g_free(proc_path);
+ return ret;
+}
diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h
index ca0d440ddc1e..5a1be712130e 100644
--- a/hw/9pfs/9p-util.h
+++ b/hw/9pfs/9p-util.h
@@ -44,5 +44,7 @@ static inline int openat_file(int dirfd, const char *name,
int flags,
}
int openat_nofollow(int dirfd, const char *path, int flags, mode_t mode);
+ssize_t fgetxattrat_nofollow(int dirfd, const char *path, const char *name,
+ void *value, size_t size);
#endif
diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c
index f87530c8b526..4071fbc4c086 100644
--- a/hw/9pfs/9p-xattr-user.c
+++ b/hw/9pfs/9p-xattr-user.c
@@ -20,9 +20,6 @@
static ssize_t mp_user_getxattr(FsContext *ctx, const char *path,
const char *name, void *value, size_t size)
{
- char *buffer;
- ssize_t ret;
-
if (strncmp(name, "user.virtfs.", 12) == 0) {
/*
* Don't allow fetch of user.virtfs namesapce
@@ -31,10 +28,7 @@ static ssize_t mp_user_getxattr(FsContext *ctx, const char
*path,
errno = ENOATTR;
return -1;
}
- buffer = rpath(ctx, path);
- ret = lgetxattr(buffer, name, value, size);
- g_free(buffer);
- return ret;
+ return local_getxattr_nofollow(ctx, path, name, value, size);
}
static ssize_t mp_user_listxattr(FsContext *ctx, const char *path,
diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c
index 19a2daf02f5c..aa4391e6b317 100644
--- a/hw/9pfs/9p-xattr.c
+++ b/hw/9pfs/9p-xattr.c
@@ -15,6 +15,8 @@
#include "9p.h"
#include "fsdev/file-op-9p.h"
#include "9p-xattr.h"
+#include "9p-util.h"
+#include "9p-local.h"
static XattrOperations *get_xattr_operations(XattrOperations **h,
@@ -143,18 +145,33 @@ int v9fs_remove_xattr(FsContext *ctx,
}
-ssize_t pt_getxattr(FsContext *ctx, const char *path, const char *name,
- void *value, size_t size)
+ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path,
+ const char *name, void *value, size_t size)
{
- char *buffer;
- ssize_t ret;
+ char *dirpath = g_path_get_dirname(path);
+ char *filename = g_path_get_basename(path);
+ int dirfd;
+ ssize_t ret = -1;
+
+ dirfd = local_opendir_nofollow(ctx, dirpath);
+ if (dirfd == -1) {
+ goto out;
+ }
- buffer = rpath(ctx, path);
- ret = lgetxattr(buffer, name, value, size);
- g_free(buffer);
+ ret = fgetxattrat_nofollow(dirfd, filename, name, value, size);
+ close_preserve_errno(dirfd);
+out:
+ g_free(dirpath);
+ g_free(filename);
return ret;
}
+ssize_t pt_getxattr(FsContext *ctx, const char *path, const char *name,
+ void *value, size_t size)
+{
+ return local_getxattr_nofollow(ctx, path, name, value, size);
+}
+
int pt_setxattr(FsContext *ctx, const char *path, const char *name, void
*value,
size_t size, int flags)
{
diff --git a/hw/9pfs/9p-xattr.h b/hw/9pfs/9p-xattr.h
index 3f43f5153f3c..69a8b6b62e3c 100644
--- a/hw/9pfs/9p-xattr.h
+++ b/hw/9pfs/9p-xattr.h
@@ -29,6 +29,8 @@ typedef struct xattr_operations
const char *path, const char *name);
} XattrOperations;
+ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path,
+ const char *name, void *value, size_t size);
extern XattrOperations mapped_user_xattr;
extern XattrOperations passthrough_user_xattr;
- [Qemu-devel] [PATCH v2 01/28] 9pfs: local: move xattr security ops to 9p-xattr.c, (continued)
- [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, 2017/02/26
- [Qemu-devel] [PATCH v2 07/28] 9pfs: local: lgetxattr: don't follow symlinks,
Greg Kurz <=
- [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
- [Qemu-devel] [PATCH v2 11/28] 9pfs: local: unlinkat: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 12/28] 9pfs: local: remove: don't follow symlinks, Greg Kurz, 2017/02/26