Re: [PATCH] binder: fix CONFIG_ANDROID_BINDER_DEVICES

[Todd Kjos]

On Sat, Jan 26, 2019 at 2:23 AM Christian Brauner <christian@xxxxxxxxxx> wrote:
>
> Several users have tried to only rely on binderfs to provide binder devices
> and set CONFIG_ANDROID_BINDER_DEVICES="" empty. This is a great use-case of
> binderfs and one that was always intended to work. However, this is
> currently not possible since setting CONFIG_ANDROID_BINDER_DEVICES="" emtpy
> will simply panic the kernel:
>
> kobject: (00000000028c2f79): attempted to be registered with empty name!
> WARNING: CPU: 7 PID: 1703 at lib/kobject.c:228 kobject_add_internal+0x288/0x2b0
> Modules linked in: binder_linux(+) bridge stp llc ipmi_ssif gpio_ich dcdbas coretemp kvm_intel kvm irqbypass serio_raw input_leds lpc_ich i5100_edac mac_hid ipmi_si ipmi_devintf ipmi_msghandler sch_fq_codel ib_i
> CPU: 7 PID: 1703 Comm: modprobe Not tainted 5.0.0-rc2-brauner-binderfs #263
> Hardware name: Dell      DCS XS24-SC2          /XS24-SC2              , BIOS S59_3C20 04/07/2011
> RIP: 0010:kobject_add_internal+0x288/0x2b0
> Code: 12 95 48 c7 c7 78 63 3b 95 e8 77 35 71 ff e9 91 fe ff ff 0f 0b eb a7 0f 0b eb 9a 48 89 de 48 c7 c7 00 63 3b 95 e8 f8 95 6a ff <0f> 0b 41 bc ea ff ff ff e9 6d fe ff ff 41 bc fe ff ff ff e9 62 fe
> RSP: 0018:ffff973f84237a30 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: ffff8b53e2472010 RCX: 0000000000000006
> RDX: 0000000000000007 RSI: 0000000000000086 RDI: ffff8b53edbd63a0
> RBP: ffff973f84237a60 R08: 0000000000000342 R09: 0000000000000004
> R10: ffff973f84237af0 R11: 0000000000000001 R12: 0000000000000000
> R13: ffff8b53e9f1a1e0 R14: 00000000e9f1a1e0 R15: 0000000000a00037
> FS:  00007fbac36f7540(0000) GS:ffff8b53edbc0000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fbac364cfa7 CR3: 00000004a6d48000 CR4: 00000000000406e0
> Call Trace:
>  kobject_add+0x71/0xd0
>  ? _cond_resched+0x19/0x40
>  ? mutex_lock+0x12/0x40
>  device_add+0x12e/0x6b0
>  device_create_groups_vargs+0xe4/0xf0
>  device_create_with_groups+0x3f/0x60
>  ? _cond_resched+0x19/0x40
>  misc_register+0x140/0x180
>  binder_init+0x1ed/0x2d4 [binder_linux]
>  ? trace_event_define_fields_binder_transaction_fd_send+0x8e/0x8e [binder_linux]
>  do_one_initcall+0x4a/0x1c9
>  ? _cond_resched+0x19/0x40
>  ? kmem_cache_alloc_trace+0x151/0x1c0
>  do_init_module+0x5f/0x216
>  load_module+0x223d/0x2b20
>  __do_sys_finit_module+0xfc/0x120
>  ? __do_sys_finit_module+0xfc/0x120
>  __x64_sys_finit_module+0x1a/0x20
>  do_syscall_64+0x5a/0x120
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7fbac3202839
> Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 8b 0d 1f f6 2c 00 f7 d8 64 89 01 48
> RSP: 002b:00007ffd1494a908 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
> RAX: ffffffffffffffda RBX: 000055b629ebec60 RCX: 00007fbac3202839
> RDX: 0000000000000000 RSI: 000055b629c20d2e RDI: 0000000000000003
> RBP: 000055b629c20d2e R08: 0000000000000000 R09: 000055b629ec2310
> R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
> R13: 000055b629ebed70 R14: 0000000000040000 R15: 000055b629ebec60
>
> So check for the empty string since strsep() will otherwise return the
> emtpy string which will cause kobject_add_internal() to panic when trying
> to add a kobject with an emtpy name.
>
> Fixes: ac4812c5ffbb ("binder: Support multiple /dev instances")
> Cc: Martijn Coenen <maco@xxxxxxxxxx>
> Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>

Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>

> ---
>  drivers/android/binder.c | 30 ++++++++++++++++--------------
>  1 file changed, 16 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 751d76173f81..5f7d6fe06eec 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -5898,21 +5898,23 @@ static int __init binder_init(void)
>                                     &transaction_log_fops);
>         }
>
> -       /*
> -        * Copy the module_parameter string, because we don't want to
> -        * tokenize it in-place.
> -        */
> -       device_names = kstrdup(binder_devices_param, GFP_KERNEL);
> -       if (!device_names) {
> -               ret = -ENOMEM;
> -               goto err_alloc_device_names_failed;
> -       }
> +       if (strcmp(binder_devices_param, "") != 0) {
> +               /*
> +               * Copy the module_parameter string, because we don't want to
> +               * tokenize it in-place.
> +                */
> +               device_names = kstrdup(binder_devices_param, GFP_KERNEL);
> +               if (!device_names) {
> +                       ret = -ENOMEM;
> +                       goto err_alloc_device_names_failed;
> +               }
>
> -       device_tmp = device_names;
> -       while ((device_name = strsep(&device_tmp, ","))) {
> -               ret = init_binder_device(device_name);
> -               if (ret)
> -                       goto err_init_binder_device_failed;
> +               device_tmp = device_names;
> +               while ((device_name = strsep(&device_tmp, ","))) {
> +                       ret = init_binder_device(device_name);
> +                       if (ret)
> +                               goto err_init_binder_device_failed;
> +               }
>         }
>
>         ret = init_binderfs();
> --
> 2.20.1
>