From a56b8d1aaf030fea196b65545dfe207ea10bdf50 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pavel=20B=C5=99ezina?= <pbrezina@redhat.com>
Date: Fri, 3 Dec 2021 13:38:44 +0100
Subject: [PATCH] utils: ignore systemd and sd-pam process in
 get_active_uid_linux()

We iterate processes in /proc to get the list of active users (users
that has any process running). However, recent change in systemd makes
systemd and sd-pam process ligner for few more seconds when the user has
logged out which breaks the no-session functionality in pam responder.

If user is logged in, another process then systemd and sd-pam must be
running. Therefore we can just ignore these from the list.

```
admin     351997  0.4  0.0  22648 14636 ?        Ss   13:25   0:00 /usr/lib/systemd/systemd --user
admin     351999  0.0  0.0 201464  7756 ?        S    13:25   0:00 (sd-pam)
```

Resolves: https://github.com/SSSD/sssd/issues/5900

:fixes: Quick log out and log in did not correctly refresh
  user's initgroups in `no_session` PAM schema due to lingering
  systemd processes.

Reviewed-by: Alexey Tikhonov <atikhono@redhat.com>
Reviewed-by: Sumit Bose <sbose@redhat.com>
---
 src/util/find_uid.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/util/find_uid.c b/src/util/find_uid.c
index 38e8f6164..1b506dfc3 100644
--- a/src/util/find_uid.c
+++ b/src/util/find_uid.c
@@ -58,7 +58,7 @@ static void hash_talloc_free(void *ptr, void *pvt)
     talloc_free(ptr);
 }
 
-static errno_t get_uid_from_pid(const pid_t pid, uid_t *uid)
+static errno_t get_uid_from_pid(const pid_t pid, uid_t *uid, bool *is_systemd)
 {
     int ret;
     char path[PATHLEN];
@@ -138,6 +138,7 @@ static errno_t get_uid_from_pid(const pid_t pid, uid_t *uid)
               "close failed [%d][%s].\n", error, strerror(error));
     }
 
+    /* Get uid */
     p = strstr(buf, "\nUid:\t");
     if (p != NULL) {
         p += 6;
@@ -165,6 +166,24 @@ static errno_t get_uid_from_pid(const pid_t pid, uid_t *uid)
         return EINVAL;
     }
 
+    /* Get process name. */
+    p = strstr(buf, "Name:\t");
+    if (p == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "format error\n");
+        return EINVAL;
+    }
+    p += 6;
+    e = strchr(p,'\n');
+    if (e == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "format error\n");
+        return EINVAL;
+    }
+    if (strncmp(p, "systemd", e-p) == 0 || strncmp(p, "(sd-pam)", e-p) == 0) {
+        *is_systemd = true;
+    } else {
+        *is_systemd = false;
+    }
+
     *uid = num;
 
     return EOK;
@@ -215,6 +234,7 @@ static errno_t get_active_uid_linux(hash_table_t *table, uid_t search_uid)
     struct dirent *dirent;
     int ret, err;
     pid_t pid = -1;
+    bool is_systemd;
     uid_t uid;
 
     hash_key_t key;
@@ -238,7 +258,7 @@ static errno_t get_active_uid_linux(hash_table_t *table, uid_t search_uid)
             goto done;
         }
 
-        ret = get_uid_from_pid(pid, &uid);
+        ret = get_uid_from_pid(pid, &uid, &is_systemd);
         if (ret != EOK) {
             /* Most probably this /proc entry disappeared.
                Anyway, just skip it.
@@ -248,6 +268,13 @@ static errno_t get_active_uid_linux(hash_table_t *table, uid_t search_uid)
             continue;
         }
 
+        if (is_systemd) {
+            /* Systemd process may linger for a while even when user.
+             * is logged out. Lets ignore it and focus only
+             * on non-systemd processes. */
+            continue;
+        }
+
         if (table != NULL) {
             key.type = HASH_KEY_ULONG;
             key.ul = (unsigned long) uid;
-- 
2.26.3