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From df7a2c629e700a510ce59b8745d240d2a43a12aa Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
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Date: Wed, 23 Jun 2021 11:46:41 +0200
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Subject: [PATCH] basic/unit-name: do not use strdupa() on a path
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The path may have unbounded length, for example through a fuse mount.
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CVE-2021-33910: attacked controlled alloca() leads to crash in systemd and
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ultimately a kernel panic. Systemd parses the content of /proc/self/mountinfo
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and each mountpoint is passed to mount_setup_unit(), which calls
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unit_name_path_escape() underneath. A local attacker who is able to mount a
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filesystem with a very long path can crash systemd and the whole system.
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https://bugzilla.redhat.com/show_bug.cgi?id=1970887
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The resulting string length is bounded by UNIT_NAME_MAX, which is 256. But we
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can't easily check the length after simplification before doing the
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simplification, which in turns uses a copy of the string we can write to.
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So we can't reject paths that are too long before doing the duplication.
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Hence the most obvious solution is to switch back to strdup(), as before
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7410616cd9dbbec97cf98d75324da5cda2b2f7a2.
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---
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src/basic/unit-name.c | 13 +++++--------
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1 file changed, 5 insertions(+), 8 deletions(-)
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diff --git a/src/basic/unit-name.c b/src/basic/unit-name.c
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index 1b81fe2..614eb86 100644
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--- a/src/basic/unit-name.c
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+++ b/src/basic/unit-name.c
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@@ -369,12 +369,13 @@ int unit_name_unescape(const char *f, char **ret) {
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}
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int unit_name_path_escape(const char *f, char **ret) {
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- char *p, *s;
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+ _cleanup_free_ char *p = NULL;
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+ char *s;
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assert(f);
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assert(ret);
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- p = strdupa(f);
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+ p = strdup(f);
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if (!p)
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return -ENOMEM;
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@@ -386,13 +387,9 @@ int unit_name_path_escape(const char *f, char **ret) {
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if (!path_is_normalized(p))
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return -EINVAL;
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- /* Truncate trailing slashes */
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+ /* Truncate trailing slashes and skip leading slashes */
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delete_trailing_chars(p, "/");
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-
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- /* Truncate leading slashes */
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- p = skip_leading_chars(p, "/");
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-
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- s = unit_name_escape(p);
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+ s = unit_name_escape(skip_leading_chars(p, "/"));
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}
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if (!s)
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return -ENOMEM;
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--
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2.31.1
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