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[Qemu-devel] [PULL 10/28] 9pfs: local: lremovexattr: don't follow symlin
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PULL 10/28] 9pfs: local: lremovexattr: don't follow symlinks |
Date: |
Tue, 28 Feb 2017 11:30:22 +0100 |
The local_lremovexattr() callback is vulnerable to symlink attacks because
it calls lremovexattr() which follows symbolic links in all path elements
but the rightmost one.
This patch introduces a helper to emulate the non-existing fremovexattrat()
function: it is implemented with /proc/self/fd which provides a trusted
path that can be safely passed to lremovexattr().
local_lremovexattr() is converted to use this helper and opendir_nofollow().
This partly fixes CVE-2016-9602.
Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
---
hw/9pfs/9p-posix-acl.c | 10 ++--------
hw/9pfs/9p-xattr-user.c | 8 +-------
hw/9pfs/9p-xattr.c | 36 +++++++++++++++++++++++++++++++-----
hw/9pfs/9p-xattr.h | 2 ++
4 files changed, 36 insertions(+), 20 deletions(-)
diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c
index 0154e2a7605f..bbf89064f7ae 100644
--- a/hw/9pfs/9p-posix-acl.c
+++ b/hw/9pfs/9p-posix-acl.c
@@ -58,10 +58,8 @@ static int mp_pacl_removexattr(FsContext *ctx,
const char *path, const char *name)
{
int ret;
- char *buffer;
- buffer = rpath(ctx, path);
- ret = lremovexattr(buffer, MAP_ACL_ACCESS);
+ ret = local_removexattr_nofollow(ctx, path, MAP_ACL_ACCESS);
if (ret == -1 && errno == ENODATA) {
/*
* We don't get ENODATA error when trying to remove a
@@ -71,7 +69,6 @@ static int mp_pacl_removexattr(FsContext *ctx,
errno = 0;
ret = 0;
}
- g_free(buffer);
return ret;
}
@@ -111,10 +108,8 @@ static int mp_dacl_removexattr(FsContext *ctx,
const char *path, const char *name)
{
int ret;
- char *buffer;
- buffer = rpath(ctx, path);
- ret = lremovexattr(buffer, MAP_ACL_DEFAULT);
+ ret = local_removexattr_nofollow(ctx, path, MAP_ACL_DEFAULT);
if (ret == -1 && errno == ENODATA) {
/*
* We don't get ENODATA error when trying to remove a
@@ -124,7 +119,6 @@ static int mp_dacl_removexattr(FsContext *ctx,
errno = 0;
ret = 0;
}
- g_free(buffer);
return ret;
}
diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c
index 1840a5db66f3..2c90817b75a6 100644
--- a/hw/9pfs/9p-xattr-user.c
+++ b/hw/9pfs/9p-xattr-user.c
@@ -81,9 +81,6 @@ static int mp_user_setxattr(FsContext *ctx, const char *path,
const char *name,
static int mp_user_removexattr(FsContext *ctx,
const char *path, const char *name)
{
- char *buffer;
- int ret;
-
if (strncmp(name, "user.virtfs.", 12) == 0) {
/*
* Don't allow fetch of user.virtfs namesapce
@@ -92,10 +89,7 @@ static int mp_user_removexattr(FsContext *ctx,
errno = EACCES;
return -1;
}
- buffer = rpath(ctx, path);
- ret = lremovexattr(buffer, name);
- g_free(buffer);
- return ret;
+ return local_removexattr_nofollow(ctx, path, name);
}
XattrOperations mapped_user_xattr = {
diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c
index a0167dd4d898..eec160b3c2ac 100644
--- a/hw/9pfs/9p-xattr.c
+++ b/hw/9pfs/9p-xattr.c
@@ -234,17 +234,43 @@ int pt_setxattr(FsContext *ctx, const char *path, const
char *name, void *value,
return local_setxattr_nofollow(ctx, path, name, value, size, flags);
}
-int pt_removexattr(FsContext *ctx, const char *path, const char *name)
+static ssize_t fremovexattrat_nofollow(int dirfd, const char *filename,
+ const char *name)
{
- char *buffer;
+ char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename);
int ret;
- buffer = rpath(ctx, path);
- ret = lremovexattr(path, name);
- g_free(buffer);
+ ret = lremovexattr(proc_path, name);
+ g_free(proc_path);
return ret;
}
+ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path,
+ const char *name)
+{
+ 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;
+ }
+
+ ret = fremovexattrat_nofollow(dirfd, filename, name);
+ close_preserve_errno(dirfd);
+out:
+ g_free(dirpath);
+ g_free(filename);
+ return ret;
+}
+
+int pt_removexattr(FsContext *ctx, const char *path, const char *name)
+{
+ return local_removexattr_nofollow(ctx, path, name);
+}
+
ssize_t notsup_getxattr(FsContext *ctx, const char *path, const char *name,
void *value, size_t size)
{
diff --git a/hw/9pfs/9p-xattr.h b/hw/9pfs/9p-xattr.h
index 7558970d8511..0d83996575e1 100644
--- a/hw/9pfs/9p-xattr.h
+++ b/hw/9pfs/9p-xattr.h
@@ -34,6 +34,8 @@ ssize_t local_getxattr_nofollow(FsContext *ctx, const char
*path,
ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path,
const char *name, void *value, size_t size,
int flags);
+ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path,
+ const char *name);
extern XattrOperations mapped_user_xattr;
extern XattrOperations passthrough_user_xattr;
--
2.7.4
- [Qemu-devel] [PULL 06/28] 9pfs: local: open/opendir: don't follow symlinks, (continued)
- [Qemu-devel] [PULL 06/28] 9pfs: local: open/opendir: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 04/28] 9pfs: introduce relative_openat_nofollow() helper, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 09/28] 9pfs: local: lsetxattr: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 07/28] 9pfs: local: lgetxattr: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 08/28] 9pfs: local: llistxattr: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 12/28] 9pfs: local: remove: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 13/28] 9pfs: local: utimensat: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 11/28] 9pfs: local: unlinkat: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 14/28] 9pfs: local: statfs: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 16/28] 9pfs: local: readlink: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 10/28] 9pfs: local: lremovexattr: don't follow symlinks,
Greg Kurz <=
- [Qemu-devel] [PULL 15/28] 9pfs: local: truncate: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 17/28] 9pfs: local: lstat: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 19/28] 9pfs: local: rename: use renameat, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 18/28] 9pfs: local: renameat: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 20/28] 9pfs: local: improve error handling in link op, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 25/28] 9pfs: local: mknod: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 22/28] 9pfs: local: chmod: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 23/28] 9pfs: local: chown: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 24/28] 9pfs: local: symlink: don't follow symlinks, Greg Kurz, 2017/02/28
- [Qemu-devel] [PULL 21/28] 9pfs: local: link: don't follow symlinks, Greg Kurz, 2017/02/28