From a88f9dbae2cbd2af6016e7f4dab5b7a0771491c6 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Mon, 31 May 2021 11:23:20 +0200 Subject: [PATCH] systemctl: unset const char* arguments in static destructors MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When fuzzing, the following happens: - we parse 'data' and produce an argv array, - one of the items in argv is assigned to arg_host, - the argv array is subsequently freed by strv_freep(), and arg_host has a dangling symlink. In normal use, argv is static, so arg_host can never become a dangling pointer. In fuzz-systemctl-parse-argv, if we repeatedly parse the same array, we have some dangling pointers while we're in the middle of parsing. If we parse the same array a second time, at the end all the dangling pointers will have been replaced again. But for a short time, if parsing one of the arguments uses another argument, we would use a dangling pointer. Such a case occurs when we have --host=… --boot-loader-entry=help. The latter calls acquire_bus() which uses arg_host. I'm not particularly happy with making the code more complicated just for fuzzing, but I think it's better to resolve this, even if the issue cannot occur in normal invocations, than to deal with fuzzer reports. Should fix https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=31714. --- src/basic/alloc-util.h | 7 +++++++ src/systemctl/systemctl-kill.c | 2 +- src/systemctl/systemctl-start-unit.c | 2 +- src/systemctl/systemctl.c | 15 ++++++++++----- src/systemctl/systemctl.h | 6 +++++- .../fuzz-systemctl-parse-argv/oss-fuzz-31714 | Bin 0 -> 132 bytes 6 files changed, 24 insertions(+), 8 deletions(-) create mode 100644 test/fuzz/fuzz-systemctl-parse-argv/oss-fuzz-31714 diff --git a/src/basic/alloc-util.h b/src/basic/alloc-util.h index 99fbd3a889e..3c33308f481 100644 --- a/src/basic/alloc-util.h +++ b/src/basic/alloc-util.h @@ -79,6 +79,13 @@ void* memdup_suffix0(const void *p, size_t l); /* We can't use _alloc_() here, s memcpy_safe(_q_, p, _l_); \ }) +static inline void unsetp(void *p) { + /* A trivial "destructor" that can be used in cases where we want to + * unset a pointer from a _cleanup_ function. */ + + *(void**)p = NULL; +} + static inline void freep(void *p) { *(void**)p = mfree(*(void**) p); } diff --git a/src/systemctl/systemctl-kill.c b/src/systemctl/systemctl-kill.c index 810aad108a3..489e7547526 100644 --- a/src/systemctl/systemctl-kill.c +++ b/src/systemctl/systemctl-kill.c @@ -22,7 +22,7 @@ int kill_unit(int argc, char *argv[], void *userdata) { arg_kill_who = "all"; /* --fail was specified */ - if (streq(arg_job_mode, "fail")) + if (streq(arg_job_mode(), "fail")) kill_who = strjoina(arg_kill_who, "-fail"); r = expand_unit_names(bus, strv_skip(argv, 1), NULL, &names, NULL); diff --git a/src/systemctl/systemctl-start-unit.c b/src/systemctl/systemctl-start-unit.c index 096b8ada200..274b278d2d6 100644 --- a/src/systemctl/systemctl-start-unit.c +++ b/src/systemctl/systemctl-start-unit.c @@ -306,7 +306,7 @@ int start_unit(int argc, char *argv[], void *userdata) { /* A command in style of "systemctl start …", "sysemctl stop …" and so on */ method = verb_to_method(argv[0]); job_type = verb_to_job_type(argv[0]); - mode = arg_job_mode; + mode = arg_job_mode(); } else method = job_type = mode = NULL; diff --git a/src/systemctl/systemctl.c b/src/systemctl/systemctl.c index a4100bd554b..e37569ab7f5 100644 --- a/src/systemctl/systemctl.c +++ b/src/systemctl/systemctl.c @@ -65,7 +65,7 @@ char **arg_states = NULL; char **arg_properties = NULL; bool arg_all = false; enum dependency arg_dependency = DEPENDENCY_FORWARD; -const char *arg_job_mode = "replace"; +const char *_arg_job_mode = NULL; UnitFileScope arg_scope = UNIT_FILE_SYSTEM; bool arg_wait = false; bool arg_no_block = false; @@ -115,8 +115,13 @@ bool arg_marked = false; STATIC_DESTRUCTOR_REGISTER(arg_types, strv_freep); STATIC_DESTRUCTOR_REGISTER(arg_states, strv_freep); STATIC_DESTRUCTOR_REGISTER(arg_properties, strv_freep); +STATIC_DESTRUCTOR_REGISTER(_arg_job_mode, unsetp); STATIC_DESTRUCTOR_REGISTER(arg_wall, strv_freep); +STATIC_DESTRUCTOR_REGISTER(arg_kill_who, unsetp); STATIC_DESTRUCTOR_REGISTER(arg_root, freep); +STATIC_DESTRUCTOR_REGISTER(arg_reboot_argument, unsetp); +STATIC_DESTRUCTOR_REGISTER(arg_host, unsetp); +STATIC_DESTRUCTOR_REGISTER(arg_boot_loader_entry, unsetp); STATIC_DESTRUCTOR_REGISTER(arg_clean_what, strv_freep); static int systemctl_help(void) { @@ -598,19 +603,19 @@ static int systemctl_parse_argv(int argc, char *argv[]) { break; case ARG_JOB_MODE: - arg_job_mode = optarg; + _arg_job_mode = optarg; break; case ARG_FAIL: - arg_job_mode = "fail"; + _arg_job_mode = "fail"; break; case ARG_IRREVERSIBLE: - arg_job_mode = "replace-irreversibly"; + _arg_job_mode = "replace-irreversibly"; break; case ARG_IGNORE_DEPENDENCIES: - arg_job_mode = "ignore-dependencies"; + _arg_job_mode = "ignore-dependencies"; break; case ARG_USER: diff --git a/src/systemctl/systemctl.h b/src/systemctl/systemctl.h index ed8152e3dd8..8199ae9e0d3 100644 --- a/src/systemctl/systemctl.h +++ b/src/systemctl/systemctl.h @@ -49,7 +49,7 @@ extern char **arg_states; extern char **arg_properties; extern bool arg_all; extern enum dependency arg_dependency; -extern const char *arg_job_mode; +extern const char *_arg_job_mode; extern UnitFileScope arg_scope; extern bool arg_wait; extern bool arg_no_block; @@ -96,4 +96,8 @@ extern bool arg_read_only; extern bool arg_mkdir; extern bool arg_marked; +static inline const char* arg_job_mode(void) { + return _arg_job_mode ?: "replace"; +} + int systemctl_dispatch_parse_argv(int argc, char *argv[]); diff --git a/test/fuzz/fuzz-systemctl-parse-argv/oss-fuzz-31714 b/test/fuzz/fuzz-systemctl-parse-argv/oss-fuzz-31714 new file mode 100644 index 0000000000000000000000000000000000000000..dfb14cd762d68516712b70256c33867cab4dbdd1 GIT binary patch literal 132 zc-mvkDA$F9VAmiAU1C9hF%tuWE(4>kZbp7_iEZfT1&s?p26*@fhcKk(l``n+Cgtas h=;q`nrlc0>rrKtt<`e)0(-JdtU}i8fFff$l0|47PAg%xa literal 0 Hc-jL100001 -- 2.47.3