tty: memory leak in tty_open

[Dmitry Vyukov]

Hello,

The following program causes a memory leak:

unreferenced object 0xffff8800643c3168 (size 2048):
  comm "syz-executor", pid 29328, jiffies 4295358628 (age 32.380s)
  hex dump (first 32 bytes):
    01 54 00 00 0c 00 00 00 88 27 e1 67 00 88 ff ff  .T.......'.g....
    88 1f 54 68 00 88 ff ff 40 b1 f0 86 ff ff ff ff  ..Th....@.......
  backtrace:
    [<ffffffff86798093>] kmemleak_alloc+0x63/0xa0 mm/kmemleak.c:915
    [<     inline     >] kmemleak_alloc_recursive include/linux/kmemleak.h:47
    [<     inline     >] slab_post_alloc_hook mm/slab.h:406
    [<     inline     >] slab_alloc_node mm/slub.c:2602
    [<     inline     >] slab_alloc mm/slub.c:2610
    [<ffffffff817979a0>] kmem_cache_alloc_trace+0x160/0x3d0 mm/slub.c:2627
    [<     inline     >] kmalloc include/linux/slab.h:478
    [<     inline     >] kzalloc include/linux/slab.h:622
    [<ffffffff8304a748>] alloc_tty_struct+0x98/0x840 drivers/tty/tty_io.c:3156
    [<ffffffff8304af68>] tty_init_dev+0x78/0x4b0 drivers/tty/tty_io.c:1532
    [<     inline     >] tty_open_by_driver drivers/tty/tty_io.c:2066
    [<ffffffff8304c181>] tty_open+0xde1/0x1140 drivers/tty/tty_io.c:2114
    [<ffffffff81801fca>] chrdev_open+0x22a/0x4c0 fs/char_dev.c:388
    [<ffffffff817ed6a2>] do_dentry_open+0x6a2/0xcb0 fs/open.c:736
    [<ffffffff817f0d7b>] vfs_open+0x17b/0x1f0 fs/open.c:853
    [<     inline     >] do_last fs/namei.c:3238
    [<ffffffff8182961b>] path_openat+0x51bb/0x5ce0 fs/namei.c:3374
    [<ffffffff8182d7be>] do_filp_open+0x18e/0x250 fs/namei.c:3409
    [<ffffffff817f14fc>] do_sys_open+0x1fc/0x420 fs/open.c:1020
    [<     inline     >] SYSC_open fs/open.c:1038
    [<ffffffff817f174d>] SyS_open+0x2d/0x40 fs/open.c:1033


// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <pthread.h>
#include <sys/syscall.h>
#include <unistd.h>

void* thr(void* arg)
{
  syscall(SYS_open, "/dev/console", 0, 0, 0, 0);
  return 0;
}

int main()
{
  int i;
  pthread_t th[4];

  for (i = 0; i < 4; i++)
    pthread_create(&th[i], 0, thr, 0);
  usleep(100);
  return 0;
}


On commit 05cf8077e54b20dddb756eaa26f3aeb5c38dd3cf (Apr 1).