bootctl: create loader.conf only if it doesn't exist yet

If the snippet aleady exists, don't do anything, as the file was already
installed then.

(This also reworks the code to create the file atomically)

Fixes: #5396

2 files changed, 31 insertions, 6 deletions

diff --git a/src/basic/fs-util.h b/src/basic/fs-util.h
index 5fe5c71ff0..094acf1799 100644
--- a/src/basic/fs-util.h
+++ b/src/basic/fs-util.h
@@ -91,3 +91,9 @@ static inline void rmdir_and_free(char *p) {
         free(p);
 }
 DEFINE_TRIVIAL_CLEANUP_FUNC(char*, rmdir_and_free);
+
+static inline void unlink_and_free(char *p) {
+        (void) unlink(p);
+        free(p);
+}
+DEFINE_TRIVIAL_CLEANUP_FUNC(char*, unlink_and_free);
diff --git a/src/boot/bootctl.c b/src/boot/bootctl.c
index 37f52c430a..116608bbd3 100644
--- a/src/boot/bootctl.c
+++ b/src/boot/bootctl.c
@@ -913,20 +913,31 @@ static int remove_variables(sd_id128_t uuid, const char *path, bool in_order) {
 
 static int install_loader_config(const char *esp_path) {
 
-        _cleanup_fclose_ FILE *f = NULL;
         char machine_string[SD_ID128_STRING_MAX];
+        _cleanup_(unlink_and_freep) char *t = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
         sd_id128_t machine_id;
         const char *p;
-        int r;
+        int r, fd;
 
         r = sd_id128_get_machine(&machine_id);
         if (r < 0)
                 return log_error_errno(r, "Failed to get machine did: %m");
 
         p = strjoina(esp_path, "/loader/loader.conf");
-        f = fopen(p, "wxe");
-        if (!f)
-                return log_error_errno(errno, "Failed to open loader.conf for writing: %m");
+
+        if (access(p, F_OK) >= 0) /* Silently skip creation if the file already exists (early check) */
+                return 0;
+
+        fd = open_tmpfile_linkable(p, O_WRONLY|O_CLOEXEC, &t);
+        if (fd < 0)
+                return log_error_errno(fd, "Failed to open \"%s\" for writing: %m", p);
+
+        f = fdopen(fd, "we");
+        if (!f) {
+                safe_close(fd);
+                return log_oom();
+        }
 
         fprintf(f, "#timeout 3\n");
         fprintf(f, "default %s-*\n", sd_id128_to_string(machine_id, machine_string));
@@ -935,7 +946,15 @@ static int install_loader_config(const char *esp_path) {
         if (r < 0)
                 return log_error_errno(r, "Failed to write \"%s\": %m", p);
 
-        return 0;
+        r = link_tmpfile(fd, t, p);
+        if (r == -EEXIST)
+                return 0; /* Silently skip creation if the file exists now (recheck) */
+        if (r < 0)
+                return log_error_errno(r, "Failed to move \"%s\" into place: %m", p);
+
+        t = mfree(t);
+
+        return 1;
 }
 
 static int help(int argc, char *argv[], void *userdata) {