commit 25e2006bff1b82c4cee3d3899ed2874815e81e4a
author Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> Wed Jun 23 11:46:41 2021 +0200
committer Jan Macku <jamacku@redhat.com> Wed Jul 28 13:00:35 2021 +0200
tree 83616e1e6b2a510b94cf6a06b0ce1ff9d689cfa2
parent bc21daeb780911d586de7ff0004ed2bc515b8826

basic/unit-name: do not use strdupa() on a path

The path may have unbounded length, for example through a fuse mount.

CVE-2021-33910: attacked controlled alloca() leads to crash in systemd and
ultimately a kernel panic. Systemd parses the content of /proc/self/mountinfo
and each mountpoint is passed to mount_setup_unit(), which calls
unit_name_path_escape() underneath. A local attacker who is able to mount a
filesystem with a very long path can crash systemd and the whole system.

https://bugzilla.redhat.com/show_bug.cgi?id=1970887

The resulting string length is bounded by UNIT_NAME_MAX, which is 256. But we
can't easily check the length after simplification before doing the
simplification, which in turns uses a copy of the string we can write to.
So we can't reject paths that are too long before doing the duplication.
Hence the most obvious solution is to switch back to strdup(), as before
7410616cd9dbbec97cf98d75324da5cda2b2f7a2.

(cherry picked from commit 441e0115646d54f080e5c3bb0ba477c892861ab9)