tun: memory leak in tun_set_iff

[Dmitry Vyukov]

Hello,

syzkaller has hit the following memory leak on 4.15-rc7.
Reproducer is attached.

unreeferenced object 0xffff88002c9ac400 (size 4096):
  comm "syz-executor0", pid 12349, jiffies 4295751114 (age 10.067s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<00000000ad172f4e>] kmemleak_alloc_recursive
include/linux/kmemleak.h:55 [inline]
    [<00000000ad172f4e>] slab_post_alloc_hook mm/slab.h:440 [inline]
    [<00000000ad172f4e>] slab_alloc_node mm/slub.c:2725 [inline]
    [<00000000ad172f4e>] slab_alloc mm/slub.c:2733 [inline]
    [<00000000ad172f4e>] __kmalloc+0x1a9/0x340 mm/slub.c:3758
    [<00000000d66b86d6>] kmalloc_array include/linux/slab.h:618 [inline]
    [<00000000d66b86d6>] kcalloc include/linux/slab.h:629 [inline]
    [<00000000d66b86d6>] __ptr_ring_init_queue_alloc
include/linux/ptr_ring.h:450 [inline]
    [<00000000d66b86d6>] ptr_ring_init include/linux/ptr_ring.h:468 [inline]
    [<00000000d66b86d6>] skb_array_init include/linux/skb_array.h:176 [inline]
    [<00000000d66b86d6>] tun_attach+0x940/0x10b0 drivers/net/tun.c:754
    [<000000007a69e5cb>] tun_set_iff drivers/net/tun.c:2315 [inline]
    [<000000007a69e5cb>] __tun_chr_ioctl+0x2435/0x4210 drivers/net/tun.c:2524
    [<000000005c75f6a6>] tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2773
    [<00000000ece2f188>] vfs_ioctl fs/ioctl.c:46 [inline]
    [<00000000ece2f188>] file_ioctl fs/ioctl.c:500 [inline]
    [<00000000ece2f188>] do_vfs_ioctl+0x1cf/0x16b0 fs/ioctl.c:684
    [<0000000021f4fda7>] SYSC_ioctl fs/ioctl.c:701 [inline]
    [<0000000021f4fda7>] SyS_ioctl+0xb6/0xe0 fs/ioctl.c:692
    [<0000000001148918>] entry_SYSCALL_64_fastpath+0x23/0x9a
    [<000000008d0cf26e>] 0xffffffffffffffff

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>

int main()
{
  syscall(__NR_mmap, 0x20000000, 0xfff000, 3, 0x32, -1, 0);
  int fd = syscall(__NR_open, "/dev/net/tun", 0);
  *(uint32_t*)0x2021b000 = 9;
  syscall(__NR_ioctl, fd, 0x400454da, 0x2021b000);
  memcpy((void*)0x20533000,
    "\x02\x00\x00\x00\x04\x00\x00\x00\x00\x04\x00\x80\x00\xe9\xbc\x22", 16);
  *(uint32_t*)0x20533010 = 0x10001;
  *(uint32_t*)0x20533014 = 0;
  *(uint64_t*)0x20533018 = 0x20012fe8;
  *(uint32_t*)0x20012fe8 = 0;
  *(uint32_t*)0x20012fec = 0;
  *(uint32_t*)0x20012ff0 = 0;
  *(uint32_t*)0x20012ff4 = 0;
  *(uint32_t*)0x20012ff8 = 0;
  *(uint16_t*)0x20012ffc = 0;
  *(uint16_t*)0x20012ffe = 0;
  syscall(__NR_ioctl, fd, 0x400454ca, 0x20533000);
  return 0;
}