mxqd: Refactor _getpwuid

mxqd.c

@@ -893,38 +893,41 @@ static int is_reaper(pid_t pid) {
         return 0;
 }
 
-static struct passwd *_getpwuid(uid_t uid, const char *name, struct passwd *pwbuf, char **bufp) {
-    long bufsize_hint = sysconf(_SC_GETPW_R_SIZE_MAX);
-    size_t bufsize = bufsize_hint > 0 ? (size_t)bufsize_hint : 1024;
-
-    for (;;) {
-        char *buf = malloc(bufsize);
-        if (!buf)
-            return NULL;
-
-        struct passwd *result;
-        int res = name ? getpwnam_r(name, pwbuf, buf, bufsize, &result)
-                        : getpwuid_r(uid,  pwbuf, buf, bufsize, &result);
-
-        if (res == 0) {
-            if (!result) {
-                free(buf);
-                errno = 0;
-                return NULL;
-            }
-            *bufp = buf;
-            return pwbuf;
-        }
+// success:               returns 0. *out is valid and needs to be freed by caller
+// success but not found: returns 0, *out is set to NULL
+// failure:               returns error number, *out is set to NULL
+//
+static int _getpw(uid_t uid, const char *name, struct passwd **out) {
+    // sysconf(_SC_GETPW_R_SIZE_MAX) is 1024 but a typical user only needs ~80 bytes.
+    // so don't bother with _SC_GETPW_R_SIZE_MAX
+    // just start with 2 * 80 = 160.
+    // note sizeof (struct passwd) is 48
+
+    size_t bufsize = 160;
 
-        free(buf);
-        if (res != ERANGE) {
-            errno = res;
-            return NULL;
+    while (1) {
+        char *block = malloc(sizeof(struct passwd) + bufsize);
+        if (!block) {
+            *out = NULL;
+            return ENOMEM;
         }
+
+        struct passwd *pwd = (struct passwd *)block;
+        char *buf = block + sizeof(struct passwd);
+
+        int res = name ? getpwnam_r(name, pwd, buf, bufsize, out)
+                        : getpwuid_r(uid,  pwd, buf, bufsize, out);
+        if (*out)
+            return res; // *out is always set. only if something found that *out != NULL and res==0.
+        free(block);
+        if (res != ERANGE)
+            return res; // 0: success (not found) or an error
         bufsize *= 2;
     }
 }
 
+// intentionally leak memory. Caller is expected to exit if we return.
+//
 static void exec_reaper(struct mxq_server *server,struct mxq_group_list *glist, struct mxq_job *job) {
     struct mxq_group *group = &glist->group;
 
@@ -944,10 +947,10 @@ static void exec_reaper(struct mxq_server *server,struct mxq_group_list *glist,
     sigprocmask(SIG_UNBLOCK,&all_signals,NULL);
     signal(SIGPIPE,SIG_DFL);
 
-    _mx_cleanup_free_ char *pwbuf = NULL;
-    struct passwd passwd_buf;
-    struct passwd *passwd = _getpwuid(group->user_uid, NULL, &passwd_buf, &pwbuf);
+    struct passwd *passwd; // initialized in next call, intentionally leaked
+    int res = _getpw(group->user_uid, NULL, &passwd);
     if (!passwd) {
+        errno = res ? res : ENOENT;
         mx_log_err("job=%s(%d):%lu:%lu getpwuid_r(): %m",
             group->user_name, group->user_uid, group->group_id, job->job_id);
         return;
@@ -963,23 +966,23 @@ static void exec_reaper(struct mxq_server *server,struct mxq_group_list *glist,
                         group->user_name,
                         passwd->pw_name);
 
-        free(pwbuf);
-        pwbuf = NULL;
-        passwd = _getpwuid(0, group->user_name, &passwd_buf, &pwbuf);
-        if (!passwd) {
+        struct passwd *passwd2; // initialized in next call, intentionally leaked
+        res = _getpw(0, group->user_name, &passwd2);
+        if (!passwd2) {
+            errno = res ? res : ENOENT;
             mx_log_err("job=%s(%d):%lu:%lu getpwnam_r(): %m",
                 group->user_name, group->user_uid, group->group_id, job->job_id);
             return;
         }
-        if (passwd->pw_uid != group->user_uid) {
+        if (passwd2->pw_uid != group->user_uid) {
             mx_log_fatal("job=%s(%d):%lu:%lu user_name=%s does not map to uid=%d but to pw_uid=%d. Aborting Child execution.",
                             group->user_name,
                             group->user_uid,
                             group->group_id,
                             job->job_id,
                             group->user_name,
                             group->user_uid,
-                            passwd->pw_uid);
+                            passwd2->pw_uid);
 
             return;
         }
@@ -1011,10 +1014,9 @@ static void exec_reaper(struct mxq_server *server,struct mxq_group_list *glist,
     if (group->job_tmpdir_size == 0) {
         mx_setenv_forever("TMPDIR", server->initial_tmpdir);
     } else {
-        char *mxq_job_tmpdir = mx_asprintf_forever("%s/%lu", MXQ_JOB_TMPDIR_MNTDIR, job->job_id);
+        char *mxq_job_tmpdir = mx_asprintf_forever("%s/%lu", MXQ_JOB_TMPDIR_MNTDIR, job->job_id); // intentionally leaked
         mx_setenv_forever("MXQ_JOB_TMPDIR", mxq_job_tmpdir);
         mx_setenv_forever("TMPDIR", mxq_job_tmpdir);
-        // not needed before exec() or exit(): free(mxq_job_tmpdir);
     }
     if (group->job_gpu) {
         char *argv[] = {