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Date:   Mon, 7 Nov 2022 22:38:35 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     Shang XiaoJing <shangxiaojing@huawei.com>
Cc:     <rostedt@goodmis.org>, <zanussi@kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] tracing: kprobe: Fix potential null-ptr-deref on
 trace_array in kprobe_event_gen_test_exit()
Message-Id: <20221107223835.4d5583852a7efef1a2ac19af@kernel.org>
In-Reply-To: <20221107071617.21644-3-shangxiaojing@huawei.com>
References: <20221107071617.21644-1-shangxiaojing@huawei.com>
        <20221107071617.21644-3-shangxiaojing@huawei.com>
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Hi,

On Mon, 7 Nov 2022 15:16:17 +0800
Shang XiaoJing <shangxiaojing@huawei.com> wrote:

> When test_gen_kprobe_cmd() failed after kprobe_event_gen_cmd_end(), it
> will goto delete, which will call kprobe_event_delete() and release the
> corresponding resource. However, the trace_array in gen_kretprobe_test
> will point to the invalid resource. Set gen_kretprobe_test->tr to NULL
> after called kprobe_event_delete() and add NULL check when releasing
> the module.
> 
> BUG: kernel NULL pointer dereference, address: 0000000000000070
> PGD 0 P4D 0
> Oops: 0000 [#1] SMP PTI
> CPU: 0 PID: 246 Comm: modprobe Tainted: G        W
> 6.1.0-rc1-00174-g9522dc5c87da-dirty #248
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
> RIP: 0010:__ftrace_set_clr_event_nolock+0x53/0x1b0
> Code: e8 82 26 fc ff 49 8b 1e c7 44 24 0c ea ff ff ff 49 39 de 0f 84 3c
> 01 00 00 c7 44 24 18 00 00 00 00 e8 61 26 fc ff 48 8b 6b 10 <44> 8b 65
> 70 4c 8b 6d 18 41 f7 c4 00 02 00 00 75 2f
> RSP: 0018:ffffc9000159fe00 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffff88810971d268 RCX: 0000000000000000
> RDX: ffff8881080be600 RSI: ffffffff811b48ff RDI: ffff88810971d058
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
> R10: ffffc9000159fe58 R11: 0000000000000001 R12: ffffffffa0001064
> R13: ffffffffa000106c R14: ffff88810971d238 R15: 0000000000000000
> FS:  00007f89eeff6540(0000) GS:ffff88813b600000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000070 CR3: 000000010599e004 CR4: 0000000000330ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __ftrace_set_clr_event+0x3e/0x60
>  trace_array_set_clr_event+0x35/0x50
>  ? 0xffffffffa0000000
>  kprobe_event_gen_test_exit+0xcd/0x10b [kprobe_event_gen_test]
>  __x64_sys_delete_module+0x206/0x380
>  ? lockdep_hardirqs_on_prepare+0xd8/0x190
>  ? syscall_enter_from_user_mode+0x1c/0x50
>  do_syscall_64+0x3f/0x90
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f89eeb061b7
> 
> Fixes: 64836248dda2 ("tracing: Add kprobe event command generation test module")
> Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
> ---
>  kernel/trace/kprobe_event_gen_test.c | 29 +++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/trace/kprobe_event_gen_test.c b/kernel/trace/kprobe_event_gen_test.c
> index 1c98fafcf333..277e21e4a63e 100644
> --- a/kernel/trace/kprobe_event_gen_test.c
> +++ b/kernel/trace/kprobe_event_gen_test.c
> @@ -145,6 +145,8 @@ static int __init test_gen_kprobe_cmd(void)
>   delete:
>  	/* We got an error after creating the event, delete it */
>  	ret = kprobe_event_delete("gen_kprobe_test");
> +	if (trace_event_file_is_valid(gen_kprobe_test))
> +		gen_kprobe_test->tr = NULL;

I think the correct fix should be

	if (trace_event_file_is_valid(gen_kprobe_test)) {
		trace_put_event_file(gen_kprobe_test);
		gen_kprobe_test = NULL;
	}
  	ret = kprobe_event_delete("gen_kprobe_test");

Since the gen_kprobe_event is owned by ftrace subsystem, the test
code should not change the tr field.

>  	goto out;
>  }
>  
> @@ -208,6 +210,8 @@ static int __init test_gen_kretprobe_cmd(void)
>   delete:
>  	/* We got an error after creating the event, delete it */
>  	ret = kprobe_event_delete("gen_kretprobe_test");
> +	if (trace_event_file_is_valid(gen_kretprobe_test))
> +		gen_kretprobe_test->tr = NULL;

Ditto.

And then, below changes are not required.

Thank you,

>  	goto out;
>  }
>  
> @@ -222,9 +226,10 @@ static int __init kprobe_event_gen_test_init(void)
>  	ret = test_gen_kretprobe_cmd();
>  	if (ret) {
>  		if (trace_event_file_is_valid(gen_kretprobe_test)) {
> -			WARN_ON(trace_array_set_clr_event(gen_kretprobe_test->tr,
> -							  "kprobes",
> -							  "gen_kretprobe_test", false));
> +			if (gen_kretprobe_test->tr)
> +				WARN_ON(trace_array_set_clr_event(gen_kretprobe_test->tr,
> +								  "kprobes",
> +								  "gen_kretprobe_test", false));
>  			trace_put_event_file(gen_kretprobe_test);
>  		}
>  		WARN_ON(kprobe_event_delete("gen_kretprobe_test"));
> @@ -236,10 +241,11 @@ static int __init kprobe_event_gen_test_init(void)
>  static void __exit kprobe_event_gen_test_exit(void)
>  {
>  	if (trace_event_file_is_valid(gen_kprobe_test)) {
> -		/* Disable the event or you can't remove it */
> -		WARN_ON(trace_array_set_clr_event(gen_kprobe_test->tr,
> -						  "kprobes",
> -						  "gen_kprobe_test", false));
> +		if (gen_kprobe_test->tr)
> +			/* Disable the event or you can't remove it */
> +			WARN_ON(trace_array_set_clr_event(gen_kprobe_test->tr,
> +							  "kprobes",
> +							  "gen_kprobe_test", false));
>  
>  		/* Now give the file and instance back */
>  		trace_put_event_file(gen_kprobe_test);
> @@ -250,10 +256,11 @@ static void __exit kprobe_event_gen_test_exit(void)
>  	WARN_ON(kprobe_event_delete("gen_kprobe_test"));
>  
>  	if (trace_event_file_is_valid(gen_kretprobe_test)) {
> -		/* Disable the event or you can't remove it */
> -		WARN_ON(trace_array_set_clr_event(gen_kretprobe_test->tr,
> -						  "kprobes",
> -						  "gen_kretprobe_test", false));
> +		if (gen_kretprobe_test->tr)
> +			/* Disable the event or you can't remove it */
> +			WARN_ON(trace_array_set_clr_event(gen_kretprobe_test->tr,
> +							  "kprobes",
> +							  "gen_kretprobe_test", false));
>  
>  		/* Now give the file and instance back */
>  		trace_put_event_file(gen_kretprobe_test);
> -- 
> 2.17.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>