Date:   Fri, 29 May 2020 21:13:32 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     syzbot <syzbot+478fd0d54412b8759e0d@...kaller.appspotmail.com>
Cc:     dledford@...hat.com, leon@...nel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, michal.kalderon@...vell.com,
        syzkaller-bugs@...glegroups.com, yishaih@...lanox.com
Subject: Re: KASAN: use-after-free Read in ib_uverbs_remove_one

On Thu, May 28, 2020 at 07:33:16AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    c11d28ab Add linux-next specific files for 20200522
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=12fc3e72100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3f6dbdea4159fb66
> dashboard link: https://syzkaller.appspot.com/bug?extid=478fd0d54412b8759e0d
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+478fd0d54412b8759e0d@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in ib_uverbs_remove_one+0x411/0x4e0 drivers/infiniband/core/uverbs_main.c:1210
> Read of size 4 at addr ffff888096324578 by task syz-executor.2/15847
> 
> CPU: 1 PID: 15847 Comm: syz-executor.2 Not tainted 5.7.0-rc6-next-20200522-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x18f/0x20d lib/dump_stack.c:118
>  print_address_description.constprop.0.cold+0xd3/0x413 mm/kasan/report.c:383
>  __kasan_report mm/kasan/report.c:513 [inline]
>  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
>  ib_uverbs_remove_one+0x411/0x4e0 drivers/infiniband/core/uverbs_main.c:1210
>  remove_client_context+0xbe/0x110 drivers/infiniband/core/device.c:732
>  disable_device+0x13b/0x230 drivers/infiniband/core/device.c:1278
>  __ib_unregister_device+0x91/0x180 drivers/infiniband/core/device.c:1445
>  ib_unregister_device_and_put+0x57/0x80 drivers/infiniband/core/device.c:1508
>  nldev_dellink+0x20a/0x310 drivers/infiniband/core/nldev.c:1571
>  rdma_nl_rcv_msg drivers/infiniband/core/netlink.c:195 [inline]
>  rdma_nl_rcv_skb drivers/infiniband/core/netlink.c:239 [inline]
>  rdma_nl_rcv+0x586/0x900 drivers/infiniband/core/netlink.c:259
>  netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
>  netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329
>  netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  ____sys_sendmsg+0x6e6/0x810 net/socket.c:2352
>  ___sys_sendmsg+0x100/0x170 net/socket.c:2406
>  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
>  do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
>  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x45ca29
> Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fd6764d1c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00000000004ffa00 RCX: 000000000045ca29
> RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000003
> RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000009af R14: 00000000004d61b0 R15: 00007fd6764d26d4
> 
> Allocated by task 9061:
>  save_stack+0x1b/0x40 mm/kasan/common.c:48
>  set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc mm/kasan/common.c:494 [inline]
>  __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:467
>  kmem_cache_alloc_trace+0x153/0x7d0 mm/slab.c:3551
>  kmalloc include/linux/slab.h:555 [inline]
>  kzalloc include/linux/slab.h:669 [inline]
>  ib_uverbs_add_one+0x80/0x7c0 drivers/infiniband/core/uverbs_main.c:1107
>  add_client_context+0x400/0x5e0 drivers/infiniband/core/device.c:677
>  enable_device_and_get+0x1cd/0x3b0 drivers/infiniband/core/device.c:1326
>  ib_register_device drivers/infiniband/core/device.c:1392 [inline]
>  ib_register_device+0xa12/0xda0 drivers/infiniband/core/device.c:1353
>  siw_device_register drivers/infiniband/sw/siw/siw_main.c:70 [inline]
>  siw_newlink drivers/infiniband/sw/siw/siw_main.c:565 [inline]
>  siw_newlink+0xd37/0x1240 drivers/infiniband/sw/siw/siw_main.c:542
>  nldev_newlink+0x29e/0x420 drivers/infiniband/core/nldev.c:1541
>  rdma_nl_rcv_msg drivers/infiniband/core/netlink.c:195 [inline]
>  rdma_nl_rcv_skb drivers/infiniband/core/netlink.c:239 [inline]
>  rdma_nl_rcv+0x586/0x900 drivers/infiniband/core/netlink.c:259
>  netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
>  netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329
>  netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  ____sys_sendmsg+0x6e6/0x810 net/socket.c:2352
>  ___sys_sendmsg+0x100/0x170 net/socket.c:2406
>  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
>  do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
>  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> 
> Freed by task 15847:
>  save_stack+0x1b/0x40 mm/kasan/common.c:48
>  set_track mm/kasan/common.c:56 [inline]
>  kasan_set_free_info mm/kasan/common.c:316 [inline]
>  __kasan_slab_free+0xf7/0x140 mm/kasan/common.c:455
>  __cache_free mm/slab.c:3426 [inline]
>  kfree+0x109/0x2b0 mm/slab.c:3757
>  device_release+0x71/0x200 drivers/base/core.c:1541
>  kobject_cleanup lib/kobject.c:701 [inline]
>  kobject_release lib/kobject.c:732 [inline]
>  kref_put include/linux/kref.h:65 [inline]
>  kobject_put+0x1c8/0x2f0 lib/kobject.c:749
>  cdev_device_del+0x69/0x80 fs/char_dev.c:575
>  ib_uverbs_remove_one+0x31/0x4e0 drivers/infiniband/core/uverbs_main.c:1209

I still can't figure out how this is possible, but I can say
cdev_device_del should not be freeing this memory - it can only mean
the uverbs_dev->dev.kref has become put several more times than it
should have.

Hopefully syzkaller will hit a refcount underflow and tell us where as
I checked every put_device obviously connected to uverbs_dev and found
nothing..

Jason

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