Re: Potential use-after-free in ____call_usermodehelper

Dmitry Vyukov
2013-08-23T15:49:08Z

On Wed, Aug 21, 2013 at 8:35 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> Hi,
>
> I'm working on a memory error detector AddressSanitizer for Linux
> kernel (https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel),
> it can detect use-after-free and buffer-overflow errors. Currently the
> tool is in very early stage and it can contain bugs.
>
> Here is one of the reports produced during testing:
>
> [ 196.951434] ERROR: AddressSanitizer: heap-use-after-free on address
> ffff880008a632c4
> [ 196.952135] Stack trace:
> [ 196.952380] [<ffffffff810dd1f5>] asan_report_error+0x85/0x2c0
> [ 196.952890] [<ffffffff810dc700>] asan_check_region+0x30/0x40
> [ 196.953466] [<ffffffff810dd553>] __tsan_write4+0x13/0x20
> [ 196.953987] [<ffffffff8110a76a>] ____call_usermodehelper+0x21a/0x240
> [ 196.954651] [<ffffffff8110a7cc>] call_helper+0x3c/0x50
> [ 196.955155] [<ffffffff81924b5c>] ret_from_fork+0x7c/0xb0
> [ 196.955686] [<ffffffffffffffff>] 0xffffffffffffffff
> [ 196.956230] Free stack trace:
> [ 196.956532] [<ffffffff810dc831>] asan_slab_free+0x61/0xb0
> [ 196.957052] [<ffffffff8128070a>] kfree+0x9a/0x240
> [ 196.957558] [<ffffffff8110a165>] call_usermodehelper_freeinfo+0x35/0x40
> [ 196.958308] [<ffffffff8110aabe>] call_usermodehelper_exec+0xae/0x1d0
> [ 196.958920] [<ffffffff8110af81>] call_usermodehelper+0x61/0x90
> [ 196.959490] [<ffffffff814d7e4e>] kobject_uevent_env+0x5be/0x5f0
> [ 196.960161] [<ffffffff814d7ea3>] kobject_uevent+0x23/0x40
> [ 196.960706] [<ffffffff814d63ad>] kobject_release+0xad/0xc0
> [ 196.961274] [<ffffffff814d618a>] kobject_put+0x3a/0x80
> [ 196.961889] [<ffffffff8181af6c>] net_rx_queue_update_kobjects+0x12c/0x170
> [ 196.962701] [<ffffffff8181b1b2>] netdev_unregister_kobject+0x62/0xa0
> [ 196.963475] [<ffffffff817f342b>] rollback_registered_many+0x27b/0x340
> [ 196.964175] [<ffffffff817f35d5>] unregister_netdevice_many+0x35/0xe0
> [ 196.964836] [<ffffffff817f43f7>] default_device_exit_batch+0x107/0x180
> [ 196.965568] [<ffffffff817ebb1c>] ops_exit_list.isra.3+0x8c/0xa0
>
>
> I've looked at the sources, but I can't say that I fully understand
> them. The report looks valid, though. I see several potential issues
> in the code.
>
> 1. When wait=UMH_WAIT_EXEC and do_execve() fails,
> ____call_usermodehelper() writes sub_info->retval=retval to freed
> memory. This is the use-after-free reported by the tool.
>
> 2. When wait=UMH_NO_WAIT, __call_usermodehelper() starts child thread
> and instantly frees subprocess_info. The child thread reads
> subprocess_info. Looks like another use-after-free.
>
> 3. UMH_WAIT_EXEC does not actually wait for exec, it only waits for
> starting the child thread that will do exec. I don't know whether it's
> a problem with the code or with the name.
>
> The kernel version is 3.11-rc4 (last commit:
> b7bc9e7d808ba55729bd263b0210cda36965be32).
>
> Please help to confirm these issues, and advice what to do next with them.
>
> TIA

Here is more detailed report with allocation stack and thread ids:

[ 957.069245] ERROR: AddressSanitizer: heap-use-after-free on address
ffff8800148452c4
[ 957.070438] Accessed by thread T22400:
[ 957.071134] #0 ffffffff810dd260 (asan_report_error+0xb0/0x250)
[ 957.071947] #1 ffffffff810dc6d0 (asan_check_region+0x30/0x40)
[ 957.072766] #2 ffffffff810dd523 (__tsan_write4+0x13/0x20)
[ 957.073559] #3 ffffffff8110a77a (____call_usermodehelper+0x21a/0x240)
[ 957.074488] #4 ffffffff8110a7dc (call_helper+0x3c/0x50)
[ 957.075266] #5 ffffffff8192569c (ret_from_fork+0x7c/0xb0)

[ 957.076006] Allocated by thread T506:
[ 957.076662] #0 ffffffff810dc794 (asan_slab_alloc+0x44/0xa0)
[ 957.077475] #1 ffffffff812821bc (__kmalloc+0xbc/0x500)
[ 957.078239] #2 ffffffff8110a1c4 (call_usermodehelper_setup+0x44/0x120)
[ 957.079173] #3 ffffffff8110af82 (call_usermodehelper+0x52/0x90)
[ 957.081469] #4 ffffffff814d831e (kobject_uevent_env+0x5be/0x5f0)
[ 957.082329] #5 ffffffff814d8373 (kobject_uevent+0x23/0x40)
[ 957.083116] #6 ffffffff814d687d (kobject_release+0xad/0xc0)
[ 957.085582] #7 ffffffff814d665a (kobject_put+0x3a/0x80)
[ 957.086348] #8 ffffffff8181b873 (netdev_queue_update_kobjects+0x133/0x1a0)
[ 957.087324] #9 ffffffff8181b94f (netdev_unregister_kobject+0x6f/0xa0)
[ 957.088232] #10 ffffffff817f3b9b (rollback_registered_many+0x27b/0x340)
[ 957.089159] #11 ffffffff817f3d45 (unregister_netdevice_many+0x35/0xe0)
[ 957.090091] #12 ffffffff817f4b67 (default_device_exit_batch+0x107/0x180)
[ 957.091010] #13 ffffffff817ec27c (ops_exit_list.isra.3+0x8c/0xa0)
[ 957.091899] #14 ffffffff817ed0c9 (cleanup_net+0x229/0x390)
[ 957.092699] #15 ffffffff811113af (process_one_work+0x2cf/0x750)

[ 957.093555] Freed by thread T506:
[ 957.094185] #0 ffffffff810dc867 (asan_slab_free+0x77/0xb0)
[ 957.094958] #1 ffffffff8128081a (kfree+0x9a/0x240)
[ 957.095659] #2 ffffffff8110a175 (call_usermodehelper_freeinfo+0x35/0x40)
[ 957.096608] #3 ffffffff8110aace (call_usermodehelper_exec+0xae/0x1d0)
[ 957.097520] #4 ffffffff8110af91 (call_usermodehelper+0x61/0x90)
[ 957.098377] #5 ffffffff814d831e (kobject_uevent_env+0x5be/0x5f0)
[ 957.099235] #6 ffffffff814d8373 (kobject_uevent+0x23/0x40)
[ 957.099984] #7 ffffffff814d687d (kobject_release+0xad/0xc0)
[ 957.100781] #8 ffffffff814d665a (kobject_put+0x3a/0x80)
[ 957.101541] #9 ffffffff8181b873 (netdev_queue_update_kobjects+0x133/0x1a0)
[ 957.102515] #10 ffffffff8181b94f (netdev_unregister_kobject+0x6f/0xa0)
[ 957.103460] #11 ffffffff817f3b9b (rollback_registered_many+0x27b/0x340)
[ 957.104419] #12 ffffffff817f3d45 (unregister_netdevice_many+0x35/0xe0)
[ 957.105352] #13 ffffffff817f4b67 (default_device_exit_batch+0x107/0x180)
[ 957.106342] #14 ffffffff817ec27c (ops_exit_list.isra.3+0x8c/0xa0)
[ 957.107182] #15 ffffffff817ed0c9 (cleanup_net+0x229/0x390)