linux-kernel - Re: [PATCH 2/2] livepatch: Fix the bug if the function name is larger than KSYM_NAME

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Date:	Mon, 13 Apr 2015 17:16:20 +0800
From:	Minfei Huang <minfei.huang@...mail.com>
To:	Petr Mladek <pmladek@...e.cz>
CC:	jpoimboe@...hat.com, sjenning@...hat.com, jkosina@...e.cz,
	vojtech@...e.cz, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] livepatch: Fix the bug if the function name is
 larger than KSYM_NAME_LEN-1

On 04/13/15 at 10:44P, Petr Mladek wrote:
> On Sun 2015-04-12 21:15:54, Minfei Huang wrote:
> > For now, the kallsyms will only store the first (KSYM_NAME_LEN-1). The
> > kallsyms name is same for the function which first (KSYM_NAME_LEN-1) is
> > same, but the rest is not.
> > 
> > Then function will never be patched, although function name and address
> > are provided both. The reason caused this bug is livepatch cannt
> > recognize the function name.
> > 
> > Now, livepatch will verify the function name with first (KSYM_NAME_LEN-1)
> > and address, if provided. Once they are matched, we can confirm that the
> > patched function is found.
> 
> This patch kind of make sense for vmlinux addresses. But are there
> functions with such a long names (>128 characters)? I hope not. They
> would never fit 80 characters per-line.
> 
> In each case, it does not make sense for modules because we are
> not able to find the symbol via old_addr.
> 

Hi, Petr.

Thanks for reviewing my patches.

Yes, You are right that the function address is changable on different
system. 

The purpose to add these patches is to avoid the case that function name
is larger enough to exceed 128.

Meanwhile I think we can not predict the behavior what user want to do.

Thanks
Minfei

> Best Regards,
> Petr
>  
> > Signed-off-by: Minfei Huang <minfei.huang@...mail.com>
> > ---
> >  kernel/livepatch/core.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index ff42c29..eed719d 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -210,7 +210,7 @@ static int klp_verify_vmlinux_callback(void *data, const char *name,
> >  	struct klp_verify_args *args = data;
> >  
> >  	if (!mod &&
> > -	    !strcmp(args->name, name) &&
> > +	    !strncmp(args->name, name, KSYM_NAME_LEN-1) &&
> >  	    args->addr == addr)
> >  		return 1;
> >  
> > @@ -226,7 +226,7 @@ static int klp_verify_module_callback(void *data, const char *name,
> >  		return 0;
> >  
> >  	if (!strcmp(args->objname, mod->name) &&
> > -	    !strcmp(args->name, name) &&
> > +	    !strncmp(args->name, name, KSYM_NAME_LEN-1) &&
> >  	    args->addr == addr)
> >  		return 1;
> >  
> > -- 
> > 2.2.2
> > 
> > --
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