From d00c14d513bbac6562a5921a2be225cfcc4f794f Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>

Date: Wed, 23 Jun 2021 11:46:41 +0200

Subject: [PATCH] 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.

Resolves: #1984299

(cherry picked from commit 441e0115646d54f080e5c3bb0ba477c892861ab9)

---

 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;