Attachment 136685 Details for Bug 104588 – _dbus_credentials_add_from_user: Add a fast-path for numeric strings

[patch] _dbus_credentials_add_from_user: Add a fast-path for numeric strings

0002-_dbus_credentials_add_from_user-Add-a-fast-path-for-.patch (text/plain), 2.01 KB, created by Simon McVittie on 2018-01-12 16:56:29 UTC

(hide)

Description:

Filename:

MIME Type:

Creator: Simon McVittie

Created: 2018-01-12 16:56:29 UTC

Size: 2.01 KB

patch

obsolete

>From 5a10b83e06268e8d447cbdfe9459be71daca5499 Mon Sep 17 00:00:00 2001
>From: Simon McVittie <smcv@collabora.com>
>Date: Fri, 12 Jan 2018 14:22:23 +0000
>Subject: [PATCH 2/7] _dbus_credentials_add_from_user: Add a fast-path for
> numeric strings
>
>The very common case for this function is that during AUTH EXTERNAL,
>it receives a Unix uid encoded as an ASCII decimal integer. There is
>no need to look up such uids in the system's user database
>(/etc/password or NSS) when the only information we are going to use
>from the DBusUserInfo struct is the uid anyway. This avoids taking
>the lock and performing a potentially time-consuming NSS lookup.
>
>This changes behaviour in one corner case: if a privileged process has
>used one of the set*uid family of functions to set its effective uid
>to a numeric uid that does not exist in the system's user database,
>we would previously fail. Now, we succeed anyway: it is true to say
>in the DBusCredentials that the process has uid 12345, even if uid
>12345 does not correspond to any named user.
>
>Signed-off-by: Simon McVittie <smcv@collabora.com>
>Bug: https://bugs.freedesktop.org/show_bug.cgi?id=104588
>---
> dbus/dbus-userdb.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
>diff --git a/dbus/dbus-userdb.c b/dbus/dbus-userdb.c
>index a07214eb..6199b855 100644
>--- a/dbus/dbus-userdb.c
>+++ b/dbus/dbus-userdb.c
>@@ -529,6 +529,18 @@ _dbus_credentials_add_from_user (DBusCredentials  *credentials,
> {
>   DBusUserDatabase *db;
>   const DBusUserInfo *info;
>+  unsigned long uid = DBUS_UID_UNSET;
>+
>+  /* Fast-path for the common case: if the "username" is all-numeric,
>+   * then it's a Unix uid. This is true regardless of whether that uid
>+   * exists in NSS or /etc/passwd or equivalent. */
>+  if (_dbus_is_a_number (username, &uid))
>+    {
>+      _DBUS_STATIC_ASSERT (sizeof (uid) == sizeof (dbus_uid_t));
>+
>+      _dbus_credentials_add_unix_uid (credentials, uid);
>+      return TRUE;
>+    }
> 
>   /* FIXME: this can't distinguish ENOMEM from other errors */
>   if (!_dbus_user_database_lock_system ())
>-- 
>2.15.1
>

Actions: View | Splinter Review

Attachments on bug 104588: 136684 | 136685 | 136686 | 136687 | 136688 | 136689 | 136690 | 136728 | 136729 | 136755

Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.