Description:
Several places in the code do not check the buffer returned by
malloc to make sure it was actually allocated.  In low memory conditions 
this call could fail, causing a null pointer exception later in the code.  In most places
the return value is checked so these seem to be exceptions rather than the norm.

This happens in the following four places:

mysqld.cpp:3220 - account_name=(char*)malloc(27);

ctype-tis620.c:545 - tc1= (uchar*) malloc(len1+len2);

ctype-tis620:577 - a= (uchar*) malloc(a_length+b_length);

regcomp.c:1066 - p->g->sets = (cset *)malloc(nc *sizeof(cset));
     else
        p->g->sets = (cset *)realloc((char *)p->g->sets, nc * sizeof(cset));

How to repeat:
Not Applicable

Suggested fix:
Check return buffer to make sure it is not null.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/internals/26421

Got the same problem on WIN XP without using the mysql_init() allocation.

The code:
#include <stdio.h>
#include <windows.h>
#include <mysql.h>

#define CONNECTION_COUNT 4

void printMemStat(void)
{
	MEMORYSTATUS memStat;
	GlobalMemoryStatus(&memStat);
	printf("FREE MEMORY %uK/%uK
(%3.2lf%%)\n",memStat.dwAvailVirtual/1024,memStat.dwTotalVirtual/1024
		,((double)memStat.dwAvailVirtual/(double)memStat.dwTotalVirtual)*100);
	printf("USED MEMORY %uK\n",(memStat.dwTotalVirtual-memStat.dwAvailVirtual)/1024);
}

int main(int argc, char *argv[])
{
	if(mysql_thread_safe())
	{
		static MYSQL conn[CONNECTION_COUNT];
		int connected[CONNECTION_COUNT]={0};
		int i=0;
		my_init();
		printf("START: ");
		printMemStat();
		for(i=0;i<CONNECTION_COUNT;i++)
		{
			printf("Before connection %d...\n",i);
			printMemStat();
			getchar();
			if(NULL!=mysql_real_connect(&conn[i],"localhost","root","sela90","kevin",3306,NULL,CLIE
NT_MULTI_STATEMENTS))
			{
				connected[i]=1;
				printf("Connected %d successfully.\n",i);
				printMemStat();
			}
			else
			{
				fprintf(stderr,"mysql_real_connect() %d error: %s\n",i,mysql_error(&conn[i]));
			}
		}
		for(i=0;i<CONNECTION_COUNT;i++)
		{
			if(connected[i])
			{
				printf("Before closing connection %d...\n",i);
				printMemStat();
				getchar();
				mysql_close(&conn[i]);
				printf("Closed connection %d.\n",i);
				printMemStat();
			}
		}
		printf("Before mysql_thread_end()....\n");
		getchar();
		mysql_thread_end();
		printf("EXIT: ");
		printMemStat();
		getchar();
	}
	else
	{
		fprintf(stderr,"MySQL client library is not thread safe. Exiting.\n");
		getchar();
	}
	return 0;
}

Ooops, wrong bug, this belongs to bug #7619.

Fixed in 5.0.14.

Documented in 5.0.11 changelog: 

<listitem><para>Added checks to prevent error when allocating memory when there was
insufficient memory available. (Bug #7003)</para></listitem>