175 lines
5.5 KiB
Diff
175 lines
5.5 KiB
Diff
From 7a95434e0ca8a037fd8aa1a2e2461f92585eb77b Mon Sep 17 00:00:00 2001
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From: Greg Kurz <groug@kaod.org>
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Date: Fri, 5 May 2017 14:48:08 +0200
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Subject: [PATCH] 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
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with the metadata. The current code already tries to hide the metadata dir
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from the client by skipping it in local_readdir(). But the client can still
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access or modify it through several other operations. This can be used to
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escalate privileges in the guest.
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Affected backend operations are:
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- local_mknod()
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- local_mkdir()
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- local_open2()
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- local_symlink()
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- local_link()
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- local_unlinkat()
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- local_renameat()
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- local_rename()
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- local_name_to_path()
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Other operations are safe because they are only passed a fid path, which
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is computed internally in local_name_to_path().
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This patch converts all the functions listed above to fail and return
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EINVAL when being passed the name of the metadata dir. This may look
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like a poor choice for errno, but there's no such thing as an illegal
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path name on Linux and I could not think of anything better.
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This fixes CVE-2017-7493.
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Reported-by: Leo Gaspard <leo@gaspard.io>
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Signed-off-by: Greg Kurz <groug@kaod.org>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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---
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hw/9pfs/9p-local.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
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1 file changed, 56 insertions(+), 2 deletions(-)
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diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
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index f3ebca4f7a..a2486566af 100644
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--- a/hw/9pfs/9p-local.c
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+++ b/hw/9pfs/9p-local.c
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@@ -452,6 +452,11 @@ static off_t local_telldir(FsContext *ctx, V9fsFidOpenState *fs)
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return telldir(fs->dir.stream);
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}
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+static bool local_is_mapped_file_metadata(FsContext *fs_ctx, const char *name)
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+{
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+ return !strcmp(name, VIRTFS_META_DIR);
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+}
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+
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static struct dirent *local_readdir(FsContext *ctx, V9fsFidOpenState *fs)
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{
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struct dirent *entry;
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@@ -465,8 +470,8 @@ again:
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if (ctx->export_flags & V9FS_SM_MAPPED) {
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entry->d_type = DT_UNKNOWN;
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} else if (ctx->export_flags & V9FS_SM_MAPPED_FILE) {
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- if (!strcmp(entry->d_name, VIRTFS_META_DIR)) {
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- /* skp the meta data directory */
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+ if (local_is_mapped_file_metadata(ctx, entry->d_name)) {
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+ /* skip the meta data directory */
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goto again;
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}
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entry->d_type = DT_UNKNOWN;
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@@ -559,6 +564,12 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
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int err = -1;
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int dirfd;
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+ if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ local_is_mapped_file_metadata(fs_ctx, name)) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
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if (dirfd == -1) {
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return -1;
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@@ -605,6 +616,12 @@ static int local_mkdir(FsContext *fs_ctx, V9fsPath *dir_path,
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int err = -1;
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int dirfd;
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+ if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ local_is_mapped_file_metadata(fs_ctx, name)) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
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if (dirfd == -1) {
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return -1;
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@@ -694,6 +711,12 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
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int err = -1;
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int dirfd;
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+ if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ local_is_mapped_file_metadata(fs_ctx, name)) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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/*
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* Mark all the open to not follow symlinks
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*/
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@@ -752,6 +775,12 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath,
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int err = -1;
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int dirfd;
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+ if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ local_is_mapped_file_metadata(fs_ctx, name)) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
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if (dirfd == -1) {
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return -1;
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@@ -826,6 +855,12 @@ static int local_link(FsContext *ctx, V9fsPath *oldpath,
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int ret = -1;
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int odirfd, ndirfd;
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+ if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ local_is_mapped_file_metadata(ctx, name)) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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odirfd = local_opendir_nofollow(ctx, odirpath);
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if (odirfd == -1) {
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goto out;
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@@ -1096,6 +1131,12 @@ static int local_lremovexattr(FsContext *ctx, V9fsPath *fs_path,
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static int local_name_to_path(FsContext *ctx, V9fsPath *dir_path,
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const char *name, V9fsPath *target)
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{
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+ if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ local_is_mapped_file_metadata(ctx, name)) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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if (dir_path) {
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v9fs_path_sprintf(target, "%s/%s", dir_path->data, name);
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} else if (strcmp(name, "/")) {
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@@ -1116,6 +1157,13 @@ static int local_renameat(FsContext *ctx, V9fsPath *olddir,
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int ret;
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int odirfd, ndirfd;
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+ if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ (local_is_mapped_file_metadata(ctx, old_name) ||
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+ local_is_mapped_file_metadata(ctx, new_name))) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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odirfd = local_opendir_nofollow(ctx, olddir->data);
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if (odirfd == -1) {
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return -1;
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@@ -1206,6 +1254,12 @@ static int local_unlinkat(FsContext *ctx, V9fsPath *dir,
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int ret;
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int dirfd;
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+ if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
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+ local_is_mapped_file_metadata(ctx, name)) {
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+ errno = EINVAL;
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+ return -1;
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+ }
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+
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dirfd = local_opendir_nofollow(ctx, dir->data);
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if (dirfd == -1) {
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return -1;
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--
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2.13.0
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