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9pfs: local: forbid client access to metadata (CVE-2017-7493)

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When using the mapped-file security mode, we shouldn't let the client mess
with the metadata. The current code already tries to hide the metadata dir
from the client by skipping it in local_readdir(). But the client can still
access or modify it through several other operations. This can be used to
escalate privileges in the guest.

Affected backend operations are:
- local_mknod()
- local_mkdir()
- local_open2()
- local_symlink()
- local_link()
- local_unlinkat()
- local_renameat()
- local_rename()
- local_name_to_path()

Other operations are safe because they are only passed a fid path, which
is computed internally in local_name_to_path().

This patch converts all the functions listed above to fail and return
EINVAL when being passed the name of the metadata dir. This may look
like a poor choice for errno, but there's no such thing as an illegal
path name on Linux and I could not think of anything better.

This fixes CVE-2017-7493.

Reported-by: Leo Gaspard <leo@gaspard.io>
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Greg Kurz 2017-05-05 14:48:08 +02:00
parent 3a8760664d
commit 7a95434e0c
1 changed files with 56 additions and 2 deletions
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58
hw/9pfs/9p-local.c
View File

@ -452,6 +452,11 @@ static off_t local_telldir(FsContext *ctx, V9fsFidOpenState *fs)
return telldir(fs->dir.stream);
}
static bool local_is_mapped_file_metadata(FsContext *fs_ctx, const char *name)
{
return !strcmp(name, VIRTFS_META_DIR);
}
static struct dirent *local_readdir(FsContext *ctx, V9fsFidOpenState *fs)
{
struct dirent *entry;
@ -465,8 +470,8 @@ again:
if (ctx->export_flags & V9FS_SM_MAPPED) {
entry->d_type = DT_UNKNOWN;
} else if (ctx->export_flags & V9FS_SM_MAPPED_FILE) {
if (!strcmp(entry->d_name, VIRTFS_META_DIR)) {
/* skp the meta data directory */
if (local_is_mapped_file_metadata(ctx, entry->d_name)) {
/* skip the meta data directory */
goto again;
}
entry->d_type = DT_UNKNOWN;
@ -559,6 +564,12 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
int err = -1;
int dirfd;
if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
local_is_mapped_file_metadata(fs_ctx, name)) {
errno = EINVAL;
return -1;
}
dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
if (dirfd == -1) {
return -1;
@ -605,6 +616,12 @@ static int local_mkdir(FsContext *fs_ctx, V9fsPath *dir_path,
int err = -1;
int dirfd;
if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
local_is_mapped_file_metadata(fs_ctx, name)) {
errno = EINVAL;
return -1;
}
dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
if (dirfd == -1) {
return -1;
@ -694,6 +711,12 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
int err = -1;
int dirfd;
if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
local_is_mapped_file_metadata(fs_ctx, name)) {
errno = EINVAL;
return -1;
}
/*
* Mark all the open to not follow symlinks
*/
@ -752,6 +775,12 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath,
int err = -1;
int dirfd;
if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
local_is_mapped_file_metadata(fs_ctx, name)) {
errno = EINVAL;
return -1;
}
dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
if (dirfd == -1) {
return -1;
@ -826,6 +855,12 @@ static int local_link(FsContext *ctx, V9fsPath *oldpath,
int ret = -1;
int odirfd, ndirfd;
if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
local_is_mapped_file_metadata(ctx, name)) {
errno = EINVAL;
return -1;
}
odirfd = local_opendir_nofollow(ctx, odirpath);
if (odirfd == -1) {
goto out;
@ -1096,6 +1131,12 @@ static int local_lremovexattr(FsContext *ctx, V9fsPath *fs_path,
static int local_name_to_path(FsContext *ctx, V9fsPath *dir_path,
const char *name, V9fsPath *target)
{
if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
local_is_mapped_file_metadata(ctx, name)) {
errno = EINVAL;
return -1;
}
if (dir_path) {
v9fs_path_sprintf(target, "%s/%s", dir_path->data, name);
} else if (strcmp(name, "/")) {
@ -1116,6 +1157,13 @@ static int local_renameat(FsContext *ctx, V9fsPath *olddir,
int ret;
int odirfd, ndirfd;
if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
(local_is_mapped_file_metadata(ctx, old_name) ||
local_is_mapped_file_metadata(ctx, new_name))) {
errno = EINVAL;
return -1;
}
odirfd = local_opendir_nofollow(ctx, olddir->data);
if (odirfd == -1) {
return -1;
@ -1206,6 +1254,12 @@ static int local_unlinkat(FsContext *ctx, V9fsPath *dir,
int ret;
int dirfd;
if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
local_is_mapped_file_metadata(ctx, name)) {
errno = EINVAL;
return -1;
}
dirfd = local_opendir_nofollow(ctx, dir->data);
if (dirfd == -1) {
return -1;