Re: [PATCH] tracing: Fix double free of event_trigger_data

[Masami Hiramatsu]

On Wed, 25 Jul 2018 08:57:40 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 
> Running the following:
> 
>  # cd /sys/kernel/debug/tracing
>  # echo 500000 > buffer_size_kb
> [ Or some other number that takes up most of memory ]
>  # echo snapshot > events/sched/sched_switch/trigger
> 
> Triggers the following bug:
> 
>  ------------[ cut here ]------------
>  kernel BUG at mm/slub.c:296!
>  invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC PTI
>  CPU: 6 PID: 6878 Comm: bash Not tainted 4.18.0-rc6-test+ #1066
>  Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v03.03 07/14/2016
>  RIP: 0010:kfree+0x16c/0x180
>  Code: 05 41 0f b6 72 51 5b 5d 41 5c 4c 89 d7 e9 ac b3 f8 ff 48 89 d9 48 89 da 41 b8 01 00 00 00 5b 5d 41 5c 4c 89 d6 e9 f4 f3 ff ff <0f> 0b 0f 0b 48 8b 3d d9 d8 f9 00 e9 c1 fe ff ff 0f 1f 40 00 0f 1f
>  RSP: 0018:ffffb654436d3d88 EFLAGS: 00010246
>  RAX: ffff91a9d50f3d80 RBX: ffff91a9d50f3d80 RCX: ffff91a9d50f3d80
>  RDX: 00000000000006a4 RSI: ffff91a9de5a60e0 RDI: ffff91a9d9803500
>  RBP: ffffffff8d267c80 R08: 00000000000260e0 R09: ffffffff8c1a56be
>  R10: fffff0d404543cc0 R11: 0000000000000389 R12: ffffffff8c1a56be
>  R13: ffff91a9d9930e18 R14: ffff91a98c0c2890 R15: ffffffff8d267d00
>  FS:  00007f363ea64700(0000) GS:ffff91a9de580000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 000055c1cacc8e10 CR3: 00000000d9b46003 CR4: 00000000001606e0
>  Call Trace:
>   event_trigger_callback+0xee/0x1d0
>   event_trigger_write+0xfc/0x1a0
>   __vfs_write+0x33/0x190
>   ? handle_mm_fault+0x115/0x230
>   ? _cond_resched+0x16/0x40
>   vfs_write+0xb0/0x190
>   ksys_write+0x52/0xc0
>   do_syscall_64+0x5a/0x160
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>  RIP: 0033:0x7f363e16ab50
>  Code: 73 01 c3 48 8b 0d 38 83 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 79 db 2c 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 1e e3 01 00 48 89 04 24
>  RSP: 002b:00007fff9a4c6378 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
>  RAX: ffffffffffffffda RBX: 0000000000000009 RCX: 00007f363e16ab50
>  RDX: 0000000000000009 RSI: 000055c1cacc8e10 RDI: 0000000000000001
>  RBP: 000055c1cacc8e10 R08: 00007f363e435740 R09: 00007f363ea64700
>  R10: 0000000000000073 R11: 0000000000000246 R12: 0000000000000009
>  R13: 0000000000000001 R14: 00007f363e4345e0 R15: 00007f363e4303c0
>  Modules linked in: ip6table_filter ip6_tables snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core snd_seq snd_seq_device i915 snd_pcm snd_timer i2c_i801 snd soundcore i2c_algo_bit drm_kms_helper
> 86_pkg_temp_thermal video kvm_intel kvm irqbypass wmi e1000e
>  ---[ end trace d301afa879ddfa25 ]---
> 
> The cause is because the register_snapshot_trigger() call failed to
> allocate the snapshot buffer, and then called unregister_trigger()
> which freed the data that was passed to it. Then on return to the
> function that called register_snapshot_trigger(), as it sees it
> failed to register, it frees the trigger_data again and causes
> a double free.
> 
> By calling event_trigger_init() on the trigger_data (which only ups
> the reference counter for it), and then event_trigger_free() afterward,
> the trigger_data would not get freed by the registering trigger function
> as it would only up and lower the ref count for it. If the register
> trigger function fails, then the event_trigger_free() called after it
> will free the trigger data normally.
> 
> Link: http://lkml.kernel.org/r/20180724191331.738eb819@xxxxxxxxxxxxxxxxxx
> 

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Thanks!

> Cc: stable@xxxxxxxxxxxxxx
> Fixes: 93e31ffbf417 ("tracing: Add 'snapshot' event trigger command")
> Reported-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
>  kernel/trace/trace_events_trigger.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> index d18249683682..d18ec0e58be2 100644
> --- a/kernel/trace/trace_events_trigger.c
> +++ b/kernel/trace/trace_events_trigger.c
> @@ -679,6 +679,8 @@ event_trigger_callback(struct event_command *cmd_ops,
>  		goto out_free;
>  
>   out_reg:
> +	/* Up the trigger_data count to make sure reg doesn't free it on failure */
> +	event_trigger_init(trigger_ops, trigger_data);
>  	ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
>  	/*
>  	 * The above returns on success the # of functions enabled,
> @@ -686,11 +688,13 @@ event_trigger_callback(struct event_command *cmd_ops,
>  	 * Consider no functions a failure too.
>  	 */
>  	if (!ret) {
> +		cmd_ops->unreg(glob, trigger_ops, trigger_data, file);
>  		ret = -ENOENT;
> -		goto out_free;
> -	} else if (ret < 0)
> -		goto out_free;
> -	ret = 0;
> +	} else if (ret > 0)
> +		ret = 0;
> +
> +	/* Down the counter of trigger_data or free it if not used anymore */
> +	event_trigger_free(trigger_ops, trigger_data);
>   out:
>  	return ret;
>  
> -- 
> 2.13.6
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>