Subject: packet mmap related oops (with reproducer)

From: Dave Jones <[email-masked]>
Date: Wed, 22 Jan 2014 17:39:20 -0500

We had a Fedora user report this bug, with a reproducer (below).

On Fri, Jan 17, 2014 at 06:52:06AM +0000, [email-masked] wrote:
 > https://bugzilla.redhat.com/show_bug.cgi?id=1054537
 > 
 > 
 > 
 > --- Comment #2 from Karl Auerbach <[email-masked]> ---
 >   --> https://bugzilla.redhat.com/attachment.cgi?id=851413
 > Simple program to cause this kernel issue
 > 
 > This is a C program that must be run with root privilege.  It runs fine on
 > older kernels but causes a kernel problem on the most recent one.
 > 
 > The code creates a raw socket with transmit and receive ring buffers.
 > 
 > The rings are then made visible via mmap().
 > 
 > When munmap() is called things go awry.
 > 
 > The code in this example was quickly lifted from a larger body of code that has
 > been running for several years.

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <unistd.h>

#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/user.h>

#include <features.h>    /* for the glibc version number */
#include <net/ethernet.h>
#include <linux/if_packet.h>
#include <linux/if_ether.h>

#include <net/if.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <linux/if_tun.h>

#define NIL   0

typedef int SOCKET;

int main(int argc, char *argv)
{
size_t              RxMmap_Size;
size_t              TxMmap_Size;
unsigned int        Ether_Sz;
unsigned int        Block_Sz_Order;
unsigned int        Block_Sz;
unsigned int        Block_Cnt;
unsigned int        Frame_Sz;
unsigned int        Frame_Cnt;
unsigned int        Frames_Per_Block;

void *              Mmap_Addr;
size_t              Mmap_Size;
size_t		    TXDataOffset;

SOCKET              Socket;

struct tpacket_req ring_req;

Ether_Sz = 1518;
Block_Sz = Ether_Sz;
Block_Sz_Order = 2; // 16384 byte blocks 
Block_Cnt = 1000;

Socket = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
if (Socket == -1)
  {
  perror("socket failed");
  return 1;
  }

Frame_Sz = TPACKET_ALIGN(TPACKET_ALIGN(TPACKET2_HDRLEN) + Ether_Sz);
TXDataOffset = TPACKET2_HDRLEN - sizeof(struct sockaddr_ll);

Block_Sz = getpagesize() << Block_Sz_Order;

Frames_Per_Block = Block_Sz / Frame_Sz;
Frame_Cnt = Frames_Per_Block * Block_Cnt;

RxMmap_Size = Block_Sz * Block_Cnt;
TxMmap_Size = RxMmap_Size;

Mmap_Size = RxMmap_Size + TxMmap_Size;

// Establish receive ring
// For convenience we will let it be the same size as the TX ring
// The mmap size calculations, far above, assume that the
// rings are the same size.
ring_req.tp_block_nr = Block_Cnt;
ring_req.tp_frame_size = Frame_Sz;
ring_req.tp_block_size = Block_Sz;
ring_req.tp_frame_nr = Frame_Cnt;
if (setsockopt(Socket, SOL_PACKET, PACKET_RX_RING,
               (char *)&ring_req, sizeof(ring_req)) < 0)
  {
  perror("Setsockopt RX_RING failed");
  close(Socket);
  return -1;
  }

// Establish transmit ring
// For convenience we will let it be the same size as the RX ring
// The mmap size calculations, far above, assume that the
// rings are the same size.
ring_req.tp_block_nr = Block_Cnt;
ring_req.tp_frame_size = Frame_Sz;
ring_req.tp_block_size = Block_Sz;
ring_req.tp_frame_nr = Frame_Cnt;
if (setsockopt(Socket, SOL_PACKET, PACKET_TX_RING,
               (char *)&ring_req, sizeof(ring_req)) < 0)
  {
  perror("Setsockopt TX_RING failed");
  close(Socket);
  return -1;
  }

Mmap_Addr = mmap(NIL, Mmap_Size, PROT_READ | PROT_WRITE,
                 MAP_SHARED | MAP_LOCKED, Socket, 0);

if (Mmap_Addr == MAP_FAILED)
  {
  perror("mmap failed");
  return 1;
  }

if (Mmap_Addr != MAP_FAILED)
  {
  (void)munmap(Mmap_Addr, Mmap_Size);
  }

close(Socket);
return 0;
}