linux-kernel - Re: [PATCH v3 1/2] printk: Fix panic caused by passing log_buf

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Date:   Sat, 22 Sep 2018 12:19:05 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     <zhe.he@...driver.com>
Cc:     <pmladek@...e.com>, <sergey.senozhatsky@...il.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] printk: Fix panic caused by passing log_buf_len
 to command line

On Sat, 22 Sep 2018 23:40:51 +0800
<zhe.he@...driver.com> wrote:

> From: He Zhe <zhe.he@...driver.com>
> 
> log_buf_len_setup does not check input argument before passing it to
> simple_strtoull. The argument would be a NULL pointer if "log_buf_len",
> without its value, is set in command line and thus causes the following
> panic.
> 
> PANIC: early exception 0xe3 IP 10:ffffffffaaeacd0d error 0 cr2 0x0
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc4-yocto-standard+ #1
> [    0.000000] RIP: 0010:_parse_integer_fixup_radix+0xd/0x70
> ...
> [    0.000000] Call Trace:
> [    0.000000]  simple_strtoull+0x29/0x70
> [    0.000000]  memparse+0x26/0x90
> [    0.000000]  log_buf_len_setup+0x17/0x22
> [    0.000000]  do_early_param+0x57/0x8e
> [    0.000000]  parse_args+0x208/0x320
> [    0.000000]  ? rdinit_setup+0x30/0x30
> [    0.000000]  parse_early_options+0x29/0x2d
> [    0.000000]  ? rdinit_setup+0x30/0x30
> [    0.000000]  parse_early_param+0x36/0x4d
> [    0.000000]  setup_arch+0x336/0x99e
> [    0.000000]  start_kernel+0x6f/0x4ee
> [    0.000000]  x86_64_start_reservations+0x24/0x26
> [    0.000000]  x86_64_start_kernel+0x6f/0x72
> [    0.000000]  secondary_startup_64+0xa4/0xb0
> 
> This patch adds a check to prevent the panic.
> 
> Signed-off-by: He Zhe <zhe.he@...driver.com>
> Cc: stable@...r.kernel.org

I just tried this on a 2.6.32 kernel, and it crashes there. I guess
this goes farther back than git history goes.

Perhaps it should be commented that this bug has been here since
creation of (git) time.


> Cc: pmladek@...e.com
> Cc: sergey.senozhatsky@...il.com
> Cc: rostedt@...dmis.org
> ---
> v2:
> Split out the addition of pr_fmt and the unsigned update

Which unsigned update? As it does switch to unsigned to "unsigned int",
but that change is fine to me with this.

> v3:
> Use more clear error info
> Change unsigned to unsigned in to avoid checkpatch.pl warning
> 
>  kernel/printk/printk.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 9bf5404..d9821c0 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1048,7 +1048,14 @@ static void __init log_buf_len_update(unsigned size)
>  /* save requested log_buf_len since it's too early to process it */
>  static int __init log_buf_len_setup(char *str)
>  {
> -	unsigned size = memparse(str, &str);
> +	unsigned int size;

I'm OK with the int update too, as its low risk.

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> +
> +	if (!str) {
> +		pr_err("boot command line parameter value not provided\n");
> +		return -EINVAL;
> +	}
> +
> +	size = memparse(str, &str);
>  
>  	log_buf_len_update(size);
>