From bae2f0d1109a8c75a7fb89ae6b8d1b6ef8dfab16 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Wed, 23 Jun 2021 11:46:41 +0200 Subject: 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. --- src/basic/unit-name.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/src/basic/unit-name.c b/src/basic/unit-name.c index 284a77348316..a22763443fdd 100644 --- a/src/basic/unit-name.c +++ b/src/basic/unit-name.c @@ -378,12 +378,13 @@ int unit_name_unescape(const char *f, char **ret) { } int unit_name_path_escape(const char *f, char **ret) { - char *p, *s; + _cleanup_free_ char *p = NULL; + char *s; assert(f); assert(ret); - p = strdupa(f); + p = strdup(f); if (!p) return -ENOMEM; @@ -395,13 +396,9 @@ int unit_name_path_escape(const char *f, char **ret) { if (!path_is_normalized(p)) return -EINVAL; - /* Truncate trailing slashes */ + /* Truncate trailing slashes and skip leading slashes */ delete_trailing_chars(p, "/"); - - /* Truncate leading slashes */ - p = skip_leading_chars(p, "/"); - - s = unit_name_escape(p); + s = unit_name_escape(skip_leading_chars(p, "/")); } if (!s) return -ENOMEM; -- 2.32.0