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systemd: do not require absolute paths in ExecStart 

Absolute paths make everything simple and quick, but sometimes this requirement
can be annoying. A good example is calling 'test', which will be located in
/usr/bin/ or /bin depending on the distro. The need the provide the full path
makes it harder a portable unit file in such cases.

This patch uses a fixed search path (DEFAULT_PATH which was already used as the
default value of $PATH), and if a non-absolute file name is found, it is
immediately resolved to a full path using this search path when the unit is
loaded. After that, everything behaves as if an absolute path was specified. In
particular, the executable must exist when the unit is loaded.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2018-03-25 20:50:15 +02:00
parent f79cd1a9b2
commit 5008da1ec1
6 changed files with 86 additions and 24 deletions
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39
man/systemd.service.xml
View File

@ -301,8 +301,9 @@
<varname>ExecStop=</varname> line set. (Services lacking both <varname>ExecStart=</varname> and
<varname>ExecStop=</varname> are not valid.)</para>
<para>For each of the specified commands, the first argument must be an absolute path to an
executable. Optionally, this filename may be prefixed with a number of special characters:</para>
<para>For each of the specified commands, the first argument must be either an absolute path to an executable
or a simple file name without any slashes. Optionally, this filename may be prefixed with a number of special
characters:</para>
<table>
<title>Special executable prefixes</title>
@ -1004,11 +1005,9 @@
<literal>&amp;</literal>, and <emphasis>other elements of shell
syntax are not supported</emphasis>.</para>
<para>The command to execute must be an absolute path name. It may
contain spaces, but control characters are not allowed.</para>
<para>The command to execute may contain spaces, but control characters are not allowed.</para>
<para>The command line accepts <literal>%</literal> specifiers as
described in
<para>The command line accepts <literal>%</literal> specifiers as described in
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>Basic environment variable substitution is supported. Use
@ -1022,10 +1021,20 @@
For this type of expansion, quotes are respected when splitting
into words, and afterwards removed.</para>
<para>If the command is not a full (absolute) path, it will be resolved to a full path using a
fixed search path determinted at compilation time. Searched directories include
<filename>/usr/local/bin/</filename>, <filename>/usr/bin/</filename>, <filename>/bin/</filename>
on systems using split <filename>/usr/bin/</filename> and <filename>/bin/</filename>
directories, and their <filename>sbin/</filename> counterparts on systems using split
<filename>bin/</filename> and <filename>sbin/</filename>. It is thus safe to use just the
executable name in case of executables located in any of the "standard" directories, and an
absolute path must be used in other cases. Using an absolute path is recommended to avoid
ambiguity.</para>
<para>Example:</para>
<programlisting>Environment="ONE=one" 'TWO=two two'
ExecStart=/bin/echo $ONE $TWO ${TWO}</programlisting>
ExecStart=echo $ONE $TWO ${TWO}</programlisting>
<para>This will execute <command>/bin/echo</command> with four
arguments: <literal>one</literal>, <literal>two</literal>,
@ -1035,7 +1044,7 @@ ExecStart=/bin/echo $ONE $TWO ${TWO}</programlisting>
<programlisting>Environment=ONE='one' "TWO='two two' too" THREE=
ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
ExecStart=/bin/echo $ONE $TWO $THREE</programlisting>
<para>This results in <filename>echo</filename> being
<para>This results in <filename>/bin/echo</filename> being
called twice, the first time with arguments
<literal>'one'</literal>,
<literal>'two two' too</literal>, <literal></literal>,
@ -1061,27 +1070,27 @@ ExecStart=/bin/echo $ONE $TWO $THREE</programlisting>
<para>Note that shell command lines are not directly supported. If
shell command lines are to be used, they need to be passed
explicitly to a shell implementation of some kind. Example:</para>
<programlisting>ExecStart=/bin/sh -c 'dmesg | tac'</programlisting>
<programlisting>ExecStart=sh -c 'dmesg | tac'</programlisting>
<para>Example:</para>
<programlisting>ExecStart=/bin/echo one ; /bin/echo "two two"</programlisting>
<programlisting>ExecStart=echo one ; echo "two two"</programlisting>
<para>This will execute <command>/bin/echo</command> two times,
<para>This will execute <command>echo</command> two times,
each time with one argument: <literal>one</literal> and
<literal>two two</literal>, respectively. Because two commands are
specified, <varname>Type=oneshot</varname> must be used.</para>
<para>Example:</para>
<programlisting>ExecStart=/bin/echo / &gt;/dev/null &amp; \; \
/bin/ls</programlisting>
<programlisting>ExecStart=echo / &gt;/dev/null &amp; \; \
ls</programlisting>
<para>This will execute <command>/bin/echo</command>
<para>This will execute <command>echo</command>
with five arguments: <literal>/</literal>,
<literal>&gt;/dev/null</literal>,
<literal>&amp;</literal>, <literal>;</literal>, and
<literal>/bin/ls</literal>.</para>
<literal>ls</literal>.</para>
<table>
<title>C escapes supported in command lines and environment variables</title>

6
src/basic/path-util.h
View File

@ -30,17 +30,23 @@
#if HAVE_SPLIT_BIN
# define PATH_SBIN_BIN(x) x "sbin:" x "bin"
# define PATH0_SBIN_BIN(x) x "sbin\0" x "bin"
#else
# define PATH0_SBIN_BIN(x) x "bin"
# define PATH_SBIN_BIN(x) x "bin"
#endif
#define DEFAULT_PATH_NORMAL PATH_SBIN_BIN("/usr/local/") ":" PATH_SBIN_BIN("/usr/")
#define DEFAULT_PATH0_NORMAL PATH0_SBIN_BIN("/usr/local/") "\0" PATH0_SBIN_BIN("/usr/")
#define DEFAULT_PATH_SPLIT_USR DEFAULT_PATH_NORMAL ":" PATH_SBIN_BIN("/")
#define DEFAULT_PATH0_SPLIT_USR DEFAULT_PATH0_NORMAL "\0" PATH0_SBIN_BIN("/")
#if HAVE_SPLIT_USR
# define DEFAULT_PATH DEFAULT_PATH_SPLIT_USR
# define DEFAULT_PATH_NULSTR DEFAULT_PATH0_SPLIT_USR
#else
# define DEFAULT_PATH DEFAULT_PATH_NORMAL
# define DEFAULT_PATH_NULSTR DEFAULT_PATH0_NORMAL
#endif
bool is_path(const char *p) _pure_;

46
src/core/load-fragment.c
View File

@ -652,23 +652,51 @@ int config_parse_exec(
}
if (!string_is_safe(path)) {
log_syntax(unit, LOG_ERR, filename, line, 0,
"Executable path contains special characters%s: %s",
ignore ? ", ignoring" : "", rvalue);
return ignore ? 0 : -ENOEXEC;
}
if (!path_is_absolute(path)) {
log_syntax(unit, LOG_ERR, filename, line, 0,
"Executable path is not absolute%s: %s",
ignore ? ", ignoring" : "", rvalue);
"Executable name contains special characters%s: %s",
ignore ? ", ignoring" : "", path);
return ignore ? 0 : -ENOEXEC;
}
if (endswith(path, "/")) {
log_syntax(unit, LOG_ERR, filename, line, 0,
"Executable path specifies a directory%s: %s",
ignore ? ", ignoring" : "", rvalue);
ignore ? ", ignoring" : "", path);
return ignore ? 0 : -ENOEXEC;
}
if (!path_is_absolute(path)) {
const char *prefix;
bool found = false;
if (!filename_is_valid(path)) {
log_syntax(unit, LOG_ERR, filename, line, 0,
"Neither a valid executable name nor an absolute path%s: %s",
ignore ? ", ignoring" : "", path);
return ignore ? 0 : -ENOEXEC;
}
/* Resolve a single-component name to a full path */
NULSTR_FOREACH(prefix, DEFAULT_PATH_NULSTR) {
_cleanup_free_ char *fullpath = NULL;
fullpath = strjoin(prefix, "/", path);
if (!fullpath)
return log_oom();
if (access(fullpath, F_OK) >= 0) {
free_and_replace(path, fullpath);
found = true;
break;
}
}
if (!found) {
log_syntax(unit, LOG_ERR, filename, line, 0,
"Executable \"%s\" not found in path \"%s\"%s",
path, DEFAULT_PATH, ignore ? ", ignoring" : "");
return ignore ? 0 : -ENOEXEC;
}
}
if (!separate_argv0) {
char *w = NULL;

5
src/test/test-execute.c
View File

@ -549,6 +549,10 @@ static void test_exec_capabilityboundingset(Manager *m) {
test(m, "exec-capabilityboundingset-invert.service", 0, CLD_EXITED);
}
static void test_exec_basic(Manager *m) {
test(m, "exec-basic.service", 0, CLD_EXITED);
}
static void test_exec_ambientcapabilities(Manager *m) {
int r;
@ -648,6 +652,7 @@ static int run_tests(UnitFileScope scope, const test_function_t *tests) {
int main(int argc, char *argv[]) {
_cleanup_(rm_rf_physical_and_freep) char *runtime_dir = NULL;
static const test_function_t user_tests[] = {
test_exec_basic,
test_exec_ambientcapabilities,
test_exec_bindpaths,
test_exec_capabilityboundingset,

1
test/meson.build
View File

@ -45,6 +45,7 @@ test_data_files = '''
sockets.target
son.service
sysinit.target
test-execute/exec-basic.service
test-execute/exec-ambientcapabilities-merge-nfsnobody.service
test-execute/exec-ambientcapabilities-merge-nobody.service
test-execute/exec-ambientcapabilities-merge.service

13
test/test-execute/exec-basic.service Normal file
View File

@ -0,0 +1,13 @@
[Unit]
Description=Test for basic execution
[Service]
ExecStart=touch /tmp/a ; /bin/touch /tmp/b ; touch /tmp/c
ExecStart=test -f /tmp/a
ExecStart=!test -f /tmp/b
ExecStart=!!test -f /tmp/c
ExecStart=+test -f /tmp/c
ExecStartPost=rm /tmp/a /tmp/b /tmp/c
PrivateTmp=true
Type=oneshot