Commit d369f207 authored by Greg Kurz's avatar Greg Kurz
Browse files

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: default avatarGreg Kurz <groug@kaod.org>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent e3187a45

hw/9pfs/9p-local.c

+17 −9
Original line number Diff line number Diff line
@@ -1160,23 +1160,31 @@ static int local_truncate(FsContext *ctx, V9fsPath *fs_path, off_t size) 


static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)

{

    char *buffer;

    char *dirpath = g_path_get_dirname(fs_path->data);

    char *name = g_path_get_basename(fs_path->data);

    int ret = -1;

    char *path = fs_path->data;

    int dirfd;



    dirfd = local_opendir_nofollow(fs_ctx, dirpath);

    if (dirfd == -1) {

        goto out;

    }



    if ((credp->fc_uid == -1 && credp->fc_gid == -1) ||

        (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) ||

        (fs_ctx->export_flags & V9FS_SM_NONE)) {

        buffer = rpath(fs_ctx, path);

        ret = lchown(buffer, credp->fc_uid, credp->fc_gid);

        g_free(buffer);

        ret = fchownat(dirfd, name, credp->fc_uid, credp->fc_gid,

                       AT_SYMLINK_NOFOLLOW);

    } else if (fs_ctx->export_flags & V9FS_SM_MAPPED) {

        buffer = rpath(fs_ctx, path);

        ret = local_set_xattr(buffer, credp);

        g_free(buffer);

        ret = local_set_xattrat(dirfd, name, credp);

    } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {

        return local_set_mapped_file_attr(fs_ctx, path, credp);

        ret = local_set_mapped_file_attrat(dirfd, name, credp);

    }



    close_preserve_errno(dirfd);

out:

    g_free(name);

    g_free(dirpath);

    return ret;

}