shared/pam-util: add pam_syslog_errno() wrapper that sets errno

So far our pam code was using strerror_safe(). But that's not a good approach,
because strerror_safe() is not thread-safe, and the pam code is "library code"
that should be thread-safe. In fact, the whole effort to use strerror() is
unnecessary, because pam_syslog() is documented to support %m. The
implementation in linux-pam simply uses vasprintf(). If we use %m too, we get
rid of the issue. The wrapper sets errno temporarily from the argument.

Apparently some PAM consumers run multiple PAM stacks in threads, so we should
avoid non-thread-safe code.

The new helper returns PAM_BUF_ERR for ENOMEM, and PAM_SERVICE_ERR in other
cases. This may change the returned code in some cases, but I think a) it
doesn't matter much, b) it's probably for the better. E.g. we might now return
PAM_SERVICE_ERR if the dbus message is borked, and PAM_SERVICE_ERR seems
appropriate.

1 files changed, 10 insertions, 18 deletions

diff --git a/src/shared/pam-util.c b/src/shared/pam-util.c
index 621e7fe802..d9fee22cc6 100644
--- a/src/shared/pam-util.c
+++ b/src/shared/pam-util.c
@@ -9,22 +9,16 @@
 #include "macro.h"
 #include "pam-util.h"
 
-int pam_log_oom(pam_handle_t *handle) {
-        /* This is like log_oom(), but uses PAM logging */
-        pam_syslog(handle, LOG_ERR, "Out of memory.");
-        return PAM_BUF_ERR;
-}
+int pam_syslog_errno(pam_handle_t *handle, int level, int error, const char *format, ...) {
+        va_list ap;
 
-int pam_bus_log_create_error(pam_handle_t *handle, int r) {
-        /* This is like bus_log_create_error(), but uses PAM logging */
-        pam_syslog(handle, LOG_ERR, "Failed to create bus message: %s", strerror_safe(r));
-        return PAM_BUF_ERR;
-}
+        LOCAL_ERRNO(error);
 
-int pam_bus_log_parse_error(pam_handle_t *handle, int r) {
-        /* This is like bus_log_parse_error(), but uses PAM logging */
-        pam_syslog(handle, LOG_ERR, "Failed to parse bus message: %s", strerror_safe(r));
-        return PAM_BUF_ERR;
+        va_start(ap, format);
+        pam_vsyslog(handle, LOG_ERR, format, ap);
+        va_end(ap);
+
+        return error == -ENOMEM ? PAM_BUF_ERR : PAM_SERVICE_ERR;
 }
 
 static void cleanup_system_bus(pam_handle_t *handle, void *data, int error_status) {
@@ -50,10 +44,8 @@ int pam_acquire_bus_connection(pam_handle_t *handle, sd_bus **ret) {
         }
 
         r = sd_bus_open_system(&bus);
-        if (r < 0) {
-                pam_syslog(handle, LOG_ERR, "Failed to connect to system bus: %s", strerror_safe(r));
-                return PAM_SERVICE_ERR;
-        }
+        if (r < 0)
+                return pam_syslog_errno(handle, LOG_ERR, r, "Failed to connect to system bus: %m");
 
         r = pam_set_data(handle, "systemd-system-bus", bus, cleanup_system_bus);
         if (r != PAM_SUCCESS) {