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Date:   Mon, 7 Nov 2022 22:25:40 +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 1/2] tracing: kprobe: Fix potential null-ptr-deref on
 trace_event_file in kprobe_event_gen_test_exit()
Message-Id: <20221107222540.1701bb267fd523fbafbbdee8@kernel.org>
In-Reply-To: <20221107071617.21644-2-shangxiaojing@huawei.com>
References: <20221107071617.21644-1-shangxiaojing@huawei.com>
        <20221107071617.21644-2-shangxiaojing@huawei.com>
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On Mon, 7 Nov 2022 15:16:16 +0800
Shang XiaoJing <shangxiaojing@huawei.com> wrote:

> When trace_get_event_file() failed, gen_kretprobe_test will be assigned
> as the error code. If module kprobe_event_gen_test is removed now, the
> null pointer dereference will happen in kprobe_event_gen_test_exit().
> Check if gen_kprobe_test or gen_kretprobe_test is error code or NULL
> before dereference them.
> 
> BUG: kernel NULL pointer dereference, address: 0000000000000012
> PGD 0 P4D 0
> Oops: 0000 [#1] SMP PTI
> CPU: 3 PID: 2210 Comm: modprobe Not tainted
> 6.1.0-rc1-00171-g2159299a3b74-dirty #217
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
> RIP: 0010:kprobe_event_gen_test_exit+0x1c/0xb5 [kprobe_event_gen_test]
> Code: Unable to access opcode bytes at 0xffffffff9ffffff2.
> RSP: 0018:ffffc900015bfeb8 EFLAGS: 00010246
> RAX: ffffffffffffffea RBX: ffffffffa0002080 RCX: 0000000000000000
> RDX: ffffffffa0001054 RSI: ffffffffa0001064 RDI: ffffffffdfc6349c
> RBP: ffffffffa0000000 R08: 0000000000000004 R09: 00000000001e95c0
> R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000800
> R13: ffffffffa0002420 R14: 0000000000000000 R15: 0000000000000000
> FS:  00007f56b75be540(0000) GS:ffff88813bc00000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffff9ffffff2 CR3: 000000010874a006 CR4: 0000000000330ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __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
> 
> Fixes: 64836248dda2 ("tracing: Add kprobe event command generation test module")

Ah, indeed. If anything wrong in the test code and if the
gen_kprobe_test/gen_kretprobe_test is not initialized, this
can happen.

Cc: stable@vger.kernel.org
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thank you!

> Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
> ---
>  kernel/trace/kprobe_event_gen_test.c | 44 ++++++++++++++++++----------
>  1 file changed, 28 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/trace/kprobe_event_gen_test.c b/kernel/trace/kprobe_event_gen_test.c
> index d81f7c51025c..1c98fafcf333 100644
> --- a/kernel/trace/kprobe_event_gen_test.c
> +++ b/kernel/trace/kprobe_event_gen_test.c
> @@ -73,6 +73,10 @@ static struct trace_event_file *gen_kretprobe_test;
>  #define KPROBE_GEN_TEST_ARG3	NULL
>  #endif
>  
> +static bool trace_event_file_is_valid(struct trace_event_file *input)
> +{
> +	return input && !IS_ERR(input);
> +}
>  
>  /*
>   * Test to make sure we can create a kprobe event, then add more
> @@ -217,10 +221,12 @@ static int __init kprobe_event_gen_test_init(void)
>  
>  	ret = test_gen_kretprobe_cmd();
>  	if (ret) {
> -		WARN_ON(trace_array_set_clr_event(gen_kretprobe_test->tr,
> -						  "kprobes",
> -						  "gen_kretprobe_test", false));
> -		trace_put_event_file(gen_kretprobe_test);
> +		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));
> +			trace_put_event_file(gen_kretprobe_test);
> +		}
>  		WARN_ON(kprobe_event_delete("gen_kretprobe_test"));
>  	}
>  
> @@ -229,24 +235,30 @@ static int __init kprobe_event_gen_test_init(void)
>  
>  static void __exit kprobe_event_gen_test_exit(void)
>  {
> -	/* 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 (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));
> +
> +		/* Now give the file and instance back */
> +		trace_put_event_file(gen_kprobe_test);
> +	}
>  
> -	/* Now give the file and instance back */
> -	trace_put_event_file(gen_kprobe_test);
>  
>  	/* Now unregister and free the event */
>  	WARN_ON(kprobe_event_delete("gen_kprobe_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 (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));
> +
> +		/* Now give the file and instance back */
> +		trace_put_event_file(gen_kretprobe_test);
> +	}
>  
> -	/* Now give the file and instance back */
> -	trace_put_event_file(gen_kretprobe_test);
>  
>  	/* Now unregister and free the event */
>  	WARN_ON(kprobe_event_delete("gen_kretprobe_test"));
> -- 
> 2.17.1
> 


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