9pfs: local: chown: don't follow symlinks
The local_chown() callback is vulnerable to symlink attacks because it calls: (1) lchown() which follows symbolic links for all path elements but the rightmost one (2) local_set_xattr()->setxattr() which follows symbolic links for all path elements (3) local_set_mapped_file_attr() which calls in turn local_fopen() and mkdir(), both functions following symbolic links for all path elements but the rightmost one This patch converts local_chown() to rely on open_nofollow() and fchownat() to fix (1), as well as local_set_xattrat() and local_set_mapped_file_attrat() to fix (2) and (3) respectively. This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz <groug@kaod.org> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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@ -1160,23 +1160,31 @@ static int local_truncate(FsContext *ctx, V9fsPath *fs_path, off_t size)
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static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
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static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
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{
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{
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char *buffer;
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char *dirpath = g_path_get_dirname(fs_path->data);
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char *name = g_path_get_basename(fs_path->data);
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int ret = -1;
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int ret = -1;
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char *path = fs_path->data;
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int dirfd;
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dirfd = local_opendir_nofollow(fs_ctx, dirpath);
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if (dirfd == -1) {
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goto out;
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}
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if ((credp->fc_uid == -1 && credp->fc_gid == -1) ||
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if ((credp->fc_uid == -1 && credp->fc_gid == -1) ||
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(fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) ||
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(fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) ||
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(fs_ctx->export_flags & V9FS_SM_NONE)) {
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(fs_ctx->export_flags & V9FS_SM_NONE)) {
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buffer = rpath(fs_ctx, path);
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ret = fchownat(dirfd, name, credp->fc_uid, credp->fc_gid,
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ret = lchown(buffer, credp->fc_uid, credp->fc_gid);
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AT_SYMLINK_NOFOLLOW);
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g_free(buffer);
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} else if (fs_ctx->export_flags & V9FS_SM_MAPPED) {
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} else if (fs_ctx->export_flags & V9FS_SM_MAPPED) {
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buffer = rpath(fs_ctx, path);
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ret = local_set_xattrat(dirfd, name, credp);
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ret = local_set_xattr(buffer, credp);
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g_free(buffer);
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} else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
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} else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
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return local_set_mapped_file_attr(fs_ctx, path, credp);
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ret = local_set_mapped_file_attrat(dirfd, name, credp);
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}
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}
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close_preserve_errno(dirfd);
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out:
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g_free(name);
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g_free(dirpath);
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return ret;
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return ret;
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}
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}
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