linux-kernel - Re: [PATCH] printk: handle blank console arguments passed in.

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Date:   Tue, 6 Oct 2020 07:08:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Shreyas Joshi <shreyas.joshi@...mp.com>, rostedt@...dmis.org,
        shreyasjoshi15@...il.com, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] printk: handle blank console arguments passed in.

On Mon, Oct 05, 2020 at 08:35:59PM -0700, Guenter Roeck wrote:
> On 10/5/20 7:59 PM, Sergey Senozhatsky wrote:
> > Cc-ing Guenter,
> > 
> > On (20/05/22 12:00), Petr Mladek wrote:
> >> On Fri 2020-05-22 16:53:06, Shreyas Joshi wrote:
> >>> If uboot passes a blank string to console_setup then it results in a trashed memory.
> >>> Ultimately, the kernel crashes during freeing up the memory. This fix checks if there
> >>> is a blank parameter being passed to console_setup from uboot.
> >>> In case it detects that the console parameter is blank then
> >>> it doesn't setup the serial device and it gracefully exits.
> >>>
> >>> Signed-off-by: Shreyas Joshi <shreyas.joshi@...mp.com>
> >>> ---
> >>>  V1:
> >>>     Fixed console_loglevel to default as per the review comments
> >>>
> >>>  kernel/printk/printk.c | 5 ++++-
> >>>  1 file changed, 4 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> >>> index ad4606234545..e9ad730991e0 100644
> >>> --- a/kernel/printk/printk.c
> >>> +++ b/kernel/printk/printk.c
> >>> @@ -2165,7 +2165,10 @@ static int __init console_setup(char *str)
> >>>  	char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
> >>>  	char *s, *options, *brl_options = NULL;
> >>>  	int idx;
> >>> -
> >>> +	if (str[0] == 0) {
> >>> +		return 1;
> >>> +	}
> >>>  	if (_braille_console_setup(&str, &brl_options))
> >>>  		return 1;
> >>
> >> I have fixed formatting and pushed it into printk/linux.git,
> >> branch for-5.8.
> > 
> > Petr, this patch's causing regressions for us. We use blank console= boot
> > param to bypass dts. It appears that it'd be better to revert the change.
> > 
> 
> Not just to bypass dts, it was also possible to use console= to disable consoles
> passed as config option, as well as other default console options. A quick test
> confirms that this affects all platforms/architectures, not just Chromebooks.
> Prior to this patch, it was possible to disable a default console with an
> empty "console=" parameter. This is no longer possible. This means that
> this patch results in a substantial (and, as far as I can see, completely
> undiscussed) functionality change.
> 
> I don't understand why (yet), but the patch also causes regressions with
> seemingly unrelated functionality, specifically with dm-verity on at least
> one Chromebook platform. I filed crbug.com/1135157 to track the problem,
> and reverted the patch from all our stable releases immediately after
> the last round of stable release merges.
> 
> On a side note, I don't see the problem presumably fixed with this
> patch in any of my tests.

I have no problem reverting this in the stable trees, but are you going
to hit this issue in Linus's tree in the next release?

thanks,

greg k-h