Merge pull request #10912 from poettering/gpt-root-rw

make sure to propagate GPT root partition r/w flag into mount r/w flag

TODO

@@ -46,9 +46,6 @@ Features:
   inserting them into the kernel keyring. Maybe SecretsDirectory= similar to
   ConfigurationDirectory=.
 
-* systemd-gpt-auto: if we find the root dir mounted read-only and the gpt flag
-  doesn't say so generate job that remounts it writable
-
 * when no locale is configured, default to UEFI's PlatformLang variable
 
 * When logind.conf contains HandleLidSwitch=suspend-then-hibernate and we can't

docs/ENVIRONMENT.md

@@ -165,3 +165,11 @@ systemd itself:
 * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
   it is either set to `system` or `user` depending on whether the NSS/PAM
   module is called by systemd in `--system` or `--user` mode.
+
+systemd-remount-fs:
+
+* `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and and no entry for the root directory
+  exists in /etc/fstab (this file always takes precedence), then the root
+  directory is remounted writable. This is primarily used by
+  systemd-gpt-auto-generator to ensure the root partition is mounted writable
+  in accordance to the GPT partition flags.

src/gpt-auto-generator/gpt-auto-generator.c

@@ -39,7 +39,7 @@
 static const char *arg_dest = NULL;
 static bool arg_enabled = true;
 static bool arg_root_enabled = true;
-static bool arg_root_rw = false;
+static int arg_root_rw = -1;
 
 static int add_cryptsetup(const char *id, const char *what, bool rw, bool require, char **device) {
         _cleanup_free_ char *e = NULL, *n = NULL, *d = NULL, *id_escaped = NULL, *what_escaped = NULL;
@@ -446,6 +446,43 @@ static int add_esp(DissectedPartition *p) {
 }
 #endif
 
+static int add_root_rw(DissectedPartition *p) {
+        const char *path;
+        int r;
+
+        assert(p);
+
+        if (in_initrd()) {
+                log_debug("In initrd, not generating drop-in for systemd-remount-fs.service.");
+                return 0;
+        }
+
+        if (arg_root_rw >= 0) {
+                log_debug("Parameter ro/rw specified on kernel command line, not generating drop-in for systemd-remount-fs.service.");
+                return 0;
+        }
+
+        if (!p->rw) {
+                log_debug("Root partition marked read-only in GPT partition table, not generating drop-in for systemd-remount-fs.service.");
+                return 0;
+        }
+
+        path = strjoina(arg_dest, "/systemd-remount-fs.service.d/50-remount-rw.conf");
+        (void) mkdir_parents(path, 0755);
+
+        r = write_string_file(path,
+                              "# Automatically generated by systemd-gpt-generator\n\n"
+                              "[Unit]\n"
+                              "ConditionPathExists=\n\n" /* We need to turn off the ConditionPathExist= in the main unit file */
+                              "[Service]\n"
+                              "Environment=SYSTEMD_REMOUNT_ROOT_RW=1\n",
+                              WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_NOFOLLOW);
+        if (r < 0)
+                return log_error_errno(r, "Failed to write drop-in file %s: %m", path);
+
+        return 0;
+}
+
 static int open_parent(dev_t devnum, int *ret) {
         _cleanup_(sd_device_unrefp) sd_device *d = NULL;
         const char *name, *devtype, *node;
@@ -550,6 +587,12 @@ static int enumerate_partitions(dev_t devnum) {
                         r = k;
         }
 
+        if (m->partitions[PARTITION_ROOT].found) {
+                k = add_root_rw(m->partitions + PARTITION_ROOT);
+                if (k < 0)
+                        r = k;
+        }
+
         return r;
 }
 
@@ -558,7 +601,8 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
 
         assert(key);
 
-        if (STR_IN_SET(key, "systemd.gpt_auto", "rd.systemd.gpt_auto")) {
+        if (proc_cmdline_key_streq(key, "systemd.gpt_auto") ||
+            proc_cmdline_key_streq(key, "rd.systemd.gpt_auto")) {
 
                 r = value ? parse_boolean(value) : 1;
                 if (r < 0)
@@ -566,7 +610,7 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
                 else
                         arg_enabled = r;
 
-        } else if (streq(key, "root")) {
+        } else if (proc_cmdline_key_streq(key, "root")) {
 
                 if (proc_cmdline_value_missing(key, value))
                         return 0;
@@ -576,7 +620,7 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
 
                 arg_root_enabled = streq(value, "gpt-auto");
 
-        } else if (streq(key, "roothash")) {
+        } else if (proc_cmdline_key_streq(key, "roothash")) {
 
                 if (proc_cmdline_value_missing(key, value))
                         return 0;
@@ -585,9 +629,9 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
 
                 arg_root_enabled = false;
 
-        } else if (streq(key, "rw") && !value)
+        } else if (proc_cmdline_key_streq(key, "rw") && !value)
                 arg_root_rw = true;
-        else if (streq(key, "ro") && !value)
+        else if (proc_cmdline_key_streq(key, "ro") && !value)
                 arg_root_rw = false;
 
         return 0;
@@ -639,7 +683,7 @@ static int add_root_mount(void) {
                         "/dev/gpt-auto-root",
                         in_initrd() ? "/sysroot" : "/",
                         NULL,
-                        arg_root_rw,
+                        arg_root_rw > 0,
                         NULL,
                         "Root Partition",
                         in_initrd() ? SPECIAL_INITRD_ROOT_FS_TARGET : SPECIAL_LOCAL_FS_TARGET);

src/remount-fs/remount-fs.c

@@ -8,6 +8,7 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
+#include "env-util.h"
 #include "exit-status.h"
 #include "log.h"
 #include "main-func.h"
@@ -19,13 +20,37 @@
 #include "strv.h"
 #include "util.h"
 
-/* Goes through /etc/fstab and remounts all API file systems, applying
- * options that are in /etc/fstab that systemd might not have
- * respected */
+/* Goes through /etc/fstab and remounts all API file systems, applying options that are in /etc/fstab that systemd
+ * might not have respected */
+
+static int track_pid(Hashmap **h, const char *path, pid_t pid) {
+        _cleanup_free_ char *c = NULL;
+        int r;
+
+        assert(h);
+        assert(path);
+        assert(pid_is_valid(pid));
+
+        r = hashmap_ensure_allocated(h, NULL);
+        if (r < 0)
+                return log_oom();
+
+        c = strdup(path);
+        if (!c)
+                return log_oom();
+
+        r = hashmap_put(*h, PID_TO_PTR(pid), c);
+        if (r < 0)
+                return log_oom();
+
+        TAKE_PTR(c);
+        return 0;
+}
 
 static int run(int argc, char *argv[]) {
         _cleanup_hashmap_free_free_ Hashmap *pids = NULL;
         _cleanup_endmntent_ FILE *f = NULL;
+        bool has_root = false;
         struct mntent* me;
         int r;
 
@@ -39,57 +64,72 @@ static int run(int argc, char *argv[]) {
 
         f = setmntent("/etc/fstab", "re");
         if (!f) {
-                if (errno == ENOENT)
-                        return 0;
+                if (errno != ENOENT)
+                        return log_error_errno(errno, "Failed to open /etc/fstab: %m");
+        } else {
+                while ((me = getmntent(f))) {
+                        pid_t pid;
 
-                return log_error_errno(errno, "Failed to open /etc/fstab: %m");
+                        /* Remount the root fs, /usr and all API VFS */
+                        if (!mount_point_is_api(me->mnt_dir) &&
+                            !PATH_IN_SET(me->mnt_dir, "/", "/usr"))
+                                continue;
+
+                        log_debug("Remounting %s...", me->mnt_dir);
+
+                        if (path_equal(me->mnt_dir, "/"))
+                                has_root = true;
+
+                        r = safe_fork("(remount)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
+                        if (r < 0)
+                                return r;
+                        if (r == 0) {
+                                /* Child */
+                                execv(MOUNT_PATH, STRV_MAKE(MOUNT_PATH, me->mnt_dir, "-o", "remount"));
+                                log_error_errno(errno, "Failed to execute " MOUNT_PATH ": %m");
+                                _exit(EXIT_FAILURE);
+                        }
+
+                        /* Parent */
+                        r = track_pid(&pids, me->mnt_dir, pid);
+                        if (r < 0)
+                                return r;
+                }
         }
 
-        pids = hashmap_new(NULL);
-        if (!pids)
-                return log_oom();
+        if (!has_root) {
+                /* The $SYSTEMD_REMOUNT_ROOT_RW environment variable is set by systemd-gpt-auto-generator to tell us
+                 * whether to remount things. We honour it only if there's no explicit line in /etc/fstab configured
+                 * which takes precedence. */
 
-        while ((me = getmntent(f))) {
-                _cleanup_free_ char *s = NULL;
-                pid_t pid;
-                int k;
+                r = getenv_bool("SYSTEMD_REMOUNT_ROOT_RW");
+                if (r > 0) {
+                        pid_t pid;
 
-                /* Remount the root fs, /usr and all API VFS */
-                if (!mount_point_is_api(me->mnt_dir) &&
-                    !path_equal(me->mnt_dir, "/") &&
-                    !path_equal(me->mnt_dir, "/usr"))
-                        continue;
+                        log_debug("Remounting / writable...");
 
-                log_debug("Remounting %s", me->mnt_dir);
+                        r = safe_fork("(remount-rw)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_LOG, &pid);
+                        if (r < 0)
+                                return r;
+                        if (r == 0) {
+                                /* Child */
+                                execv(MOUNT_PATH, STRV_MAKE(MOUNT_PATH, "/", "-o", "remount,rw"));
+                                log_error_errno(errno, "Failed to execute " MOUNT_PATH ": %m");
+                                _exit(EXIT_FAILURE);
+                        }
 
-                r = safe_fork("(remount)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
-                if (r < 0)
-                        return r;
-                if (r == 0) {
-                        /* Child */
+                        r = track_pid(&pids, "/", pid);
+                        if (r < 0)
+                                return r;
 
-                        execv(MOUNT_PATH, STRV_MAKE(MOUNT_PATH, me->mnt_dir, "-o", "remount"));
-
-                        log_error_errno(errno, "Failed to execute " MOUNT_PATH ": %m");
-                        _exit(EXIT_FAILURE);
-                }
-
-                /* Parent */
-
-                s = strdup(me->mnt_dir);
-                if (!s)
-                        return log_oom();
-
-                k = hashmap_put(pids, PID_TO_PTR(pid), s);
-                if (k < 0)
-                        return log_oom();
-                TAKE_PTR(s);
+                } else if (r < 0 && r != -ENXIO)
+                        log_warning_errno(r, "Failed to parse $SYSTEMD_REMOUNT_ROOT_RW, ignoring: %m");
         }
 
         r = 0;
         while (!hashmap_isempty(pids)) {
-                siginfo_t si = {};
                 _cleanup_free_ char *s = NULL;
+                siginfo_t si = {};
 
                 if (waitid(P_ALL, 0, &si, WEXITED) < 0) {
                         if (errno == EINTR)