sysctl: add --verify option to verify written values (#43258)

man/systemd-sysctl.service.xml

@@ -62,7 +62,7 @@
 
   <refsect1><title>Options</title>
     <variablelist>
-      <varlistentry id='prefix'>
+      <varlistentry>
         <term><option>--prefix=</option></term>
         <listitem>
           <para>Only apply rules with the specified prefix.</para>
@@ -70,8 +70,8 @@
         <xi:include href="version-info.xml" xpointer="v230"/>
         </listitem>
       </varlistentry>
-      <varlistentry id='strict'>
-        <term><option>--strict=</option></term>
+      <varlistentry>
+        <term><option>--strict</option></term>
         <listitem>
           <para>Always return non-zero exit code on failure (including invalid sysctl variable
           name and insufficient permissions), unless the sysctl variable name is prefixed with a "-"
@@ -81,6 +81,15 @@
         </listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>--verify</option></term>
+        <listitem>
+          <para>Verify sysctl values after write.</para>
+
+          <xi:include href="version-info.xml" xpointer="v262"/>
+        </listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><option>--inline</option></term>
         <listitem><para>Treat each positional argument as a separate configuration line instead of a file

src/basic/sysctl-util.c

@@ -114,6 +114,43 @@ int sysctl_writef(const char *property, const char *format, ...) {
         return sysctl_write(property, v);
 }
 
+int sysctl_write_verify(const char *property, const char *value) {
+        int r;
+
+        assert(property);
+        assert(value);
+
+        /* Some sysctl settings accept invalid values on write, but refuses on read. E.g. coredump pattern,
+         * be1e0283021ec73c2eb92839db9a471a068709d9 (v6.17) and 7d7c1fb85cba5627bbe741fb7539c709435e3848
+         * (v6.16.8), which is fixed by a779e27f24aeb679969ddd1fdd7f636e22ddbc1e (v6.18) and
+         * 304aa560385720baf3660fe8500f6dd425b63ea9 (v6.17.5). Let's first save the original value, and
+         * restore to the saved value if the new value is refused. */
+
+        _cleanup_free_ char *original = NULL;
+        r = sysctl_read(property, &original);
+        if (r >= 0 && streq(original, value))
+                return 0; /* Already set. */
+
+        r = sysctl_write(property, value);
+        if (r >= 0) {
+                _cleanup_free_ char *current = NULL;
+                r = sysctl_read(property, &current);
+                if (r >= 0) {
+                        if (streq(current, value))
+                                return 0; /* Yay! */
+
+                        /* At least for coredump pattern, this does not happen, but let's handle this as the
+                         * same as we wrote something invalid. */
+                        r = -EINVAL;
+                }
+        }
+
+        if (original)
+                (void) sysctl_write(property, original);
+
+        return r;
+}
+
 static const char* af_to_sysctl_dir(int af) {
         if (af == AF_MPLS)
                 return "mpls";

src/basic/sysctl-util.h

@@ -12,6 +12,7 @@ int sysctl_writef(const char *property, const char *format, ...) _printf_(2, 3);
 static inline int sysctl_write(const char *property, const char *value) {
         return sysctl_write_full(property, value, NULL);
 }
+int sysctl_write_verify(const char *property, const char *value);
 
 int sysctl_read_ip_property(int af, const char *ifname, const char *property, char **ret);
 int sysctl_read_ip_property_int(int af, const char *ifname, const char *property, int *ret);

src/sysctl/sysctl.c

@@ -25,6 +25,7 @@
 static char **arg_prefixes = NULL;
 static CatFlags arg_cat_flags = CAT_CONFIG_OFF;
 static bool arg_strict = false;
+static bool arg_verify = false;
 static bool arg_inline = false;
 static PagerFlags arg_pager_flags = 0;
 
@@ -89,7 +90,10 @@ static SysctlOption* sysctl_option_new(
 static int sysctl_write_or_warn(const char *key, const char *value, bool ignore_failure, bool ignore_enoent) {
         int r;
 
-        r = sysctl_write(key, value);
+        if (arg_verify)
+                r = sysctl_write_verify(key, value);
+        else
+                r = sysctl_write(key, value);
         if (r < 0) {
                 /* Proceed without failing if ignore_failure is true.
                  * If the sysctl is not available in the kernel or we are running with reduced privileges and
@@ -409,6 +413,11 @@ static int parse_argv(int argc, char *argv[], char ***remaining_args) {
                         arg_strict = true;
                         break;
 
+                OPTION_LONG("verify", NULL,
+                            "Verify sysctl values after write"):
+                        arg_verify = true;
+                        break;
+
                 OPTION_LONG("inline", NULL,
                             "Treat arguments as configuration lines"):
                         arg_inline = true;
@@ -425,18 +434,18 @@ static int parse_argv(int argc, char *argv[], char ***remaining_args) {
 }
 
 static int run(int argc, char *argv[]) {
-        _cleanup_ordered_hashmap_free_ OrderedHashmap *sysctl_options = NULL;
         int r;
 
+        log_setup();
+
         char **args = NULL;
         r = parse_argv(argc, argv, &args);
         if (r <= 0)
                 return r;
 
-        log_setup();
-
         umask(0022);
 
+        _cleanup_ordered_hashmap_free_ OrderedHashmap *sysctl_options = NULL;
         if (!strv_isempty(args)) {
                 unsigned pos = 0;
 

test/units/TEST-87-AUX-UTILS-VM.sysctl.sh

@@ -78,3 +78,16 @@ EOF
 assert_eq "$(cat /proc/sys/net/ipv4/conf/hoge/drop_gratuitous_arp)" "1"
 assert_eq "$(cat /proc/sys/net/ipv4/conf/hoge/bootp_relay)" "1"
 assert_eq "$(cat /proc/sys/net/ipv4/conf/hoge/disable_policy)" "0"
+
+echo 0 >/proc/sys/net/ipv4/conf/hoge/drop_gratuitous_arp
+echo 0 >/proc/sys/net/ipv4/conf/hoge/bootp_relay
+echo 0 >/proc/sys/net/ipv4/conf/hoge/disable_policy
+
+/usr/lib/systemd/systemd-sysctl --prefix=/net/ipv4/conf/hoge --verify - <<EOF
+net.ipv4.conf.*.drop_gratuitous_arp=1
+net.ipv4.*.*.bootp_relay=1
+net.ipv4.aaa.*.disable_policy=1
+EOF
+assert_eq "$(cat /proc/sys/net/ipv4/conf/hoge/drop_gratuitous_arp)" "1"
+assert_eq "$(cat /proc/sys/net/ipv4/conf/hoge/bootp_relay)" "1"
+assert_eq "$(cat /proc/sys/net/ipv4/conf/hoge/disable_policy)" "0"