From 441e0115646d54f080e5c3bb0ba477c892861ab9 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: [PATCH 1/2] 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 284a773483..a22763443f 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; From 4e2544c30bfb95e7cb4d1551ba066b1a56520ad6 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Wed, 23 Jun 2021 11:52:56 +0200 Subject: [PATCH 2/2] basic/unit-name: adjust comments MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit We already checked for "too long" right above… --- src/basic/unit-name.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/basic/unit-name.c b/src/basic/unit-name.c index a22763443f..1deead7458 100644 --- a/src/basic/unit-name.c +++ b/src/basic/unit-name.c @@ -528,7 +528,7 @@ int unit_name_from_path(const char *path, const char *suffix, char **ret) { if (strlen(s) >= UNIT_NAME_MAX) /* Return a slightly more descriptive error for this specific condition */ return -ENAMETOOLONG; - /* Refuse this if this got too long or for some other reason didn't result in a valid name */ + /* Refuse if this for some other reason didn't result in a valid name */ if (!unit_name_is_valid(s, UNIT_NAME_PLAIN)) return -EINVAL; @@ -562,7 +562,7 @@ int unit_name_from_path_instance(const char *prefix, const char *path, const cha if (strlen(s) >= UNIT_NAME_MAX) /* Return a slightly more descriptive error for this specific condition */ return -ENAMETOOLONG; - /* Refuse this if this got too long or for some other reason didn't result in a valid name */ + /* Refuse if this for some other reason didn't result in a valid name */ if (!unit_name_is_valid(s, UNIT_NAME_INSTANCE)) return -EINVAL;