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From 17e1ee2539cea6bac16832b488afd52b20a348ac Mon Sep 17 00:00:00 2001
From: Rainer Gerhards <rgerhards@adiscon.com>
Date: Mon, 28 Oct 2013 14:17:56 +0100
Subject: [PATCH] remove memleak introduced by GenerateLocalHostName HUP
bugfix
Upstream-Status: backport
Signed-off-by: Li Zhou <li.zhou@windriver.com>
---
runtime/glbl.c | 45 ++++++++++++++++++++++++++++++++-------------
1 file changed, 32 insertions(+), 13 deletions(-)
diff --git a/runtime/glbl.c b/runtime/glbl.c
index bcb3795..41d56c2 100644
--- a/runtime/glbl.c
+++ b/runtime/glbl.c
@@ -72,6 +72,7 @@ static int option_DisallowWarning = 1; /* complain if message from disallowed se
static int bDisableDNS = 0; /* don't look up IP addresses of remote messages */
static prop_t *propLocalIPIF = NULL;/* IP address to report for the local host (default is 127.0.0.1) */
static prop_t *propLocalHostName = NULL;/* our hostname as FQDN - read-only after startup */
+static prop_t *propLocalHostNameToDelete = NULL;/* see GenerateLocalHostName function hdr comment! */
static uchar *LocalHostName = NULL;/* our hostname - read-only after startup, except HUP */
static uchar *LocalHostNameOverride = NULL;/* user-overridden hostname - read-only after startup */
static uchar *LocalFQDNName = NULL;/* our hostname as FQDN - read-only after startup, except HUP */
@@ -380,24 +381,31 @@ GetLocalDomain(void)
/* generate the local hostname property. This must be done after the hostname info
* has been set as well as PreserveFQDN.
* rgerhards, 2009-06-30
- * NOTE: This function DELIBERATELY introduces a small memory leak in order to gain
- * speed. Each time it is called when a property name already exists, a new one is
- * allocated but the previous one is NOT freed. This is so that current readers can
- * continue to use the previous name. Otherwise, we would need to use read/write locks
- * to protect the update process. As this function is called extremely infrequently and
- * the memory leak is very small, this is totally accessible. Think that otherwise we
- * would need to place a read look each time the property is read, which is much more
- * frequent (once per message for the modules that use this local hostname!).
+ * NOTE: This function tries to avoid locking by not destructing the previous value
+ * immediately. This is so that current readers can continue to use the previous name.
+ * Otherwise, we would need to use read/write locks to protect the update process.
+ * In order to do so, we save the previous value and delete it when we are called again
+ * the next time. Note that this in theory is racy and can lead to a double-free.
+ * In practice, however, the window of exposure to trigger this is extremely short
+ * and as this functions is very infrequently being called (on HUP), the trigger
+ * condition for this bug is so highly unlikely that it never occurs in practice.
+ * Probably if you HUP rsyslog every few milliseconds, but who does that...
+ * To further reduce risk potential, we do only update the property when there
+ * actually is a hostname change, which makes it even less likely.
* rgerhards, 2013-10-28
*/
static rsRetVal
GenerateLocalHostNameProperty(void)
{
+ uchar *pszPrev;
+ int lenPrev;
prop_t *hostnameNew;
uchar *pszName;
DEFiRet;
- CHKiRet(prop.Construct(&hostnameNew));
+ if(propLocalHostNameToDelete != NULL)
+ prop.Destruct(&propLocalHostNameToDelete);
+
if(LocalHostNameOverride == NULL) {
if(LocalHostName == NULL)
pszName = (uchar*) "[localhost]";
@@ -411,11 +419,20 @@ GenerateLocalHostNameProperty(void)
pszName = LocalHostNameOverride;
}
DBGPRINTF("GenerateLocalHostName uses '%s'\n", pszName);
- CHKiRet(prop.SetString(hostnameNew, pszName, ustrlen(pszName)));
- CHKiRet(prop.ConstructFinalize(hostnameNew));
- propLocalHostName = hostnameNew;
- /* inititional MEM LEAK for old value -- see function hdr comment! */
+ if(propLocalHostName == NULL)
+ pszPrev = (uchar*)""; /* make sure strcmp() below does not match */
+ else
+ prop.GetString(propLocalHostName, &pszPrev, &lenPrev);
+
+ if(ustrcmp(pszPrev, pszName)) {
+ /* we need to update */
+ CHKiRet(prop.Construct(&hostnameNew));
+ CHKiRet(prop.SetString(hostnameNew, pszName, ustrlen(pszName)));
+ CHKiRet(prop.ConstructFinalize(hostnameNew));
+ propLocalHostNameToDelete = propLocalHostName;
+ propLocalHostName = hostnameNew;
+ }
finalize_it:
RETiRet;
@@ -678,6 +695,8 @@ BEGINObjClassExit(glbl, OBJ_IS_CORE_MODULE) /* class, version */
free(LocalHostNameOverride);
free(LocalFQDNName);
objRelease(prop, CORE_COMPONENT);
+ if(propLocalHostNameToDelete != NULL)
+ prop.Destruct(&propLocalHostNameToDelete);
DESTROY_ATOMIC_HELPER_MUT(mutTerminateInputs);
ENDObjClassExit(glbl)
--
1.7.9.5
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