diff options
| -rw-r--r-- | runtime/glbl.c | 45 |
1 files changed, 32 insertions, 13 deletions
diff --git a/runtime/glbl.c b/runtime/glbl.c index bcb37953..41d56c2c 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) |