Commits on Nov 24, 2023

1. Fix memory corruption while calling SysV msgsnd & msgrcv …

   Here is a snippet of man page for msgsnd & msgrcv,
   
   ```
         int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);
   
          ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp,
                         int msgflg);
   
   DESCRIPTION
          The  msgsnd() and msgrcv() system calls are used to send messages to, and receive messages from, a System V message queue.  The calling process must have write
          permission on the message queue in order to send a message, and read permission to receive a message.
   
          The msgp argument is a pointer to a caller-defined structure of the following general form:
   
              struct msgbuf {
                  long mtype;       /* message type, must be > 0 */
                  char mtext[1];    /* message data */
              };
   
          The mtext field is an array (or other structure) whose size is specified by msgsz, a nonnegative integer value.  Messages of zero length (i.e., no mtext field)
          are  permitted.   The  mtype field must have a strictly positive integer value.  This value can be used by the receiving process for message selection (see the
          description of msgrcv() below).
   ```
   
   According to it, the 3rd arg of both msgsnd and msgrcv must pass the
   size of mtext i.e. excluding the mtype.
   
   If we apply this logic into our context, we must pass the sizeof(QMessage->data), not sizeof(QMessage).
   
   We can also find the corruption using valgrind like below,
   
   ```
   valgrind --trace-children=yes --tool=memcheck --leak-check=no pgcopydb
   copy table-data
   ```
   
   It gives the following summary,
   
   ```
   ==640986== Syscall param msgsnd(msgp->mtext) points to uninitialised byte(s)
   ==640986==    at 0x4AC92AA: msgsnd (msgsnd.c:25)
   ==640986==    by 0x14E178: queue_send (queue_utils.c:100)
   ==640986==    by 0x162643: UnknownInlinedFun (table-data.c:403)
   ==640986==    by 0x162643: UnknownInlinedFun (table-data.c:295)
   ==640986==    by 0x162643: UnknownInlinedFun (table-data.c:232)
   ==640986==    by 0x162643: UnknownInlinedFun (table-data.c:209)
   ==640986==    by 0x162643: UnknownInlinedFun (table-data.c:117)
   ==640986==    by 0x162643: UnknownInlinedFun (table-data.c:89)
   ==640986==    by 0x162643: copydb_copy_all_table_data (table-data.c:57)
   ==640986==    by 0x11406E: cli_copy_table_data (cli_copy.c:395)
   ==640986==    by 0x1118B2: UnknownInlinedFun (commandline.c:71)
   ==640986==    by 0x1118B2: main (main.c:142)
   ==640986==  Address 0x1ffeeec5f0 is on thread 1's stack
   ==640986==  in frame #2, created by copydb_copy_all_table_data (table-data.c:38)
   ==640986==
   ==640986== Syscall param msgsnd(msgp->mtext) points to uninitialised byte(s)
   ==640986==    at 0x4AC92AA: msgsnd (msgsnd.c:25)
   ==640986==    by 0x14E178: queue_send (queue_utils.c:100)
   ==640986==    by 0x162AD8: UnknownInlinedFun (table-data.c:380)
   ==640986==    by 0x162AD8: UnknownInlinedFun (table-data.c:307)
   ==640986==    by 0x162AD8: UnknownInlinedFun (table-data.c:232)
   ==640986==    by 0x162AD8: UnknownInlinedFun (table-data.c:209)
   ==640986==    by 0x162AD8: UnknownInlinedFun (table-data.c:117)
   ==640986==    by 0x162AD8: UnknownInlinedFun (table-data.c:89)
   ==640986==    by 0x162AD8: copydb_copy_all_table_data (table-data.c:57)
   ==640986==    by 0x11406E: cli_copy_table_data (cli_copy.c:395)
   ==640986==    by 0x1118B2: UnknownInlinedFun (commandline.c:71)
   ==640986==    by 0x1118B2: main (main.c:142)
   ==640986==  Address 0x1ffeeec5f0 is on thread 1's stack
   ==640986==  in frame #2, created by copydb_copy_all_table_data (table-data.c:38)
   ==640986==
   
   ...
   ```
   
   The above error disappers with the fix.
   
   Signed-off-by: Arunprasad Rajkumar <ar.arunprasad@gmail.com>

   

   arajkumar committed Nov 24, 2023
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