Question 192300 in Mysql Question posted in
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SIGSEGV on simple mysql_query in C using Mariadb

I have a function that I query my database:

void update_layout_database()
  char query[255];
  MYSQL_ROW row;
  float wd,ht;
  sprintf(query,"SELECT name,wd,ht FROM pagelayouts WHERE drawing=%s AND handle=%ld;",drawing_number,layoutID);
  mysql_query(sqlconnect,query);
  MYSQL_RES *result = mysql_store_result(sqlconnect);
  row=mysql_fetch_row(result);
  if(row!=NULL){
    if(atof(row[1])==0 || atof(row[2])==0 || !strcmp(row[0],"Model")){
      wd=Extents[2]-Extents[0];
      ht=Extents[3]-Extents[1];
      sprintf(query,"UPDATE pagelayouts SET X=%f, Y=%f,wd=%f,ht=%f WHERE drawing=%s AND handle=%ld",Extents[0],Extents[1],wd,ht,drawing_number,layoutID);
      mysql_query(sqlconnect,query);
    }
  }
}

Variables sqlconnect, drawing_number, layoutID and Extents are global declared in the root of the script.

MYSQL *sqlconnect=NULL;
char * drawing_number, layoutID;
float Extents[4]={0,0,0,0};

The database is intialised:

void initialize_database(char *dBase)
{
  char * Dname=(char *)malloc(strlen(dBase+2));
  sprintf(Dname,"prefix%s",dBase);
  sqlconnect=mysql_init(sqlconnect);
  if (!mysql_real_connect(sqlconnect, "localhost", "dgman", "xxxxxxxxxxxxxxx", Dname, 0, NULL, 0))
  {
    fprintf(stderr, "Unable to connect to MariaDB servern");
    exit(1);
  }
  mysql_set_character_set(sqlconnect, "utf8");
}

According to GDB, the value of ‘sqlconnect’ is properly instantiated:GDB screenshot showing the value of 'sqlconnect' and 'query'

The same screenshot shows the contents of the ‘query’ string.

I’m baffled.

Can anyone suggest how I can solve this?

GDB Screenshot of backtrace'

Tags:

2

Answers


  1. 0

    You have a crash inside malloc implementation.

    99.999% of such crashes are caused by heap corruption (heap buffer overflow, freeing something twice, freeing unallocated memory, etc. etc.).

    These bugs are ~impossible to find without proper tools, because the bug often manifests itself in a place that is far removed from where the actual problem occurs.

    Fortunately we do have tools which help you find the root cause: Valgrind and Address Sanitizer.

    Use them and you will likely be pointed straight at the problem.

    P.S. You should never use sprintf — it’s a recipe for buffer overflow. Always use snprintf instead.

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  2. 0 
    char * Dname=(char *)malloc(strlen(dBase+2));
sprintf(Dname,"prefix%s",dBase);

    strlen("prefix") + the null is > 2

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