Re: [PATCHv2] jump_label: check entries limit in __jump_label_update

[Jason Baron <jbaron@redhat.com>]

On Tue, May 10, 2011 at 12:43:46PM +0200, Jiri Olsa wrote:
> On Mon, May 09, 2011 at 03:32:48PM -0400, Jason Baron wrote:
> > On Wed, May 04, 2011 at 05:30:23PM +0200, Jiri Olsa wrote:
> > > When iterating the jump_label entries array (core or modules),
> > > the __jump_label_update function peeks over the last entry.
> > > 
> > > The reason is that the end of the for loop depends on the key
> > > value of the processed entry. Thus when going through the
> > > last array entry, we will touch the memory behind the array
> > > limit.
> > > 
> > > This bug probably will never be triggered, since most likely the
> > > memory behind the jump_label entries will be accesable and the
> > > entry->key will be different than the expected value.
> > > 
> > > 
> > > Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> > > ---
> > >  kernel/jump_label.c |   17 ++++++++++++-----
> > >  1 files changed, 12 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> > > index 74d1c09..b2ee97a 100644
> > > --- a/kernel/jump_label.c
> > > +++ b/kernel/jump_label.c
> > > @@ -105,9 +105,12 @@ static int __jump_label_text_reserved(struct jump_entry *iter_start,
> > >  }
> > >  
> > >  static void __jump_label_update(struct jump_label_key *key,
> > > -		struct jump_entry *entry, int enable)
> > > +				struct jump_entry *entry,
> > > +				struct jump_entry *stop, int enable)
> > >  {
> > > -	for (; entry->key == (jump_label_t)(unsigned long)key; entry++) {
> > > +	for (; (entry < stop) &&
> > > +	      (entry->key == (jump_label_t)(unsigned long)key);
> > > +	      entry++) {
> > >  		/*
> > >  		 * entry->code set to 0 invalidates module init text sections
> > >  		 * kernel_text_address() verifies we are not in core kernel
> > > @@ -158,6 +161,7 @@ early_initcall(jump_label_init);
> > >  struct jump_label_mod {
> > >  	struct jump_label_mod *next;
> > >  	struct jump_entry *entries;
> > > +	struct jump_entry *entries_stop;
> > >  	struct module *mod;
> > >  };
> > >  
> > > @@ -181,7 +185,8 @@ static void __jump_label_mod_update(struct jump_label_key *key, int enable)
> > >  	struct jump_label_mod *mod = key->next;
> > >  
> > >  	while (mod) {
> > > -		__jump_label_update(key, mod->entries, enable);
> > > +		__jump_label_update(key, mod->entries, mod->entries_stop,
> > > +				    enable);
> > >  		mod = mod->next;
> > 
> > hmmm. Instead of adding a new field to the 'struct jump_label_mod' data
> > structure (and thus increasing its footprint), why not use:
> > mod->jump_entries +  mod->num_jump_entries here?
> 
> yep, overlooked the struct module pointer inside jump_label_mod
> attaching new patch
> 
> thanks,
> jirka
>  
> ---
> When iterating the jump_label entries array (core or modules),
> the __jump_label_update function peeks over the last entry.
> 
> The reason is that the end of the for loop depends on the key
> value of the processed entry. Thus when going through the
> last array entry, we will touch the memory behind the array
> limit.
> 
> This bug probably will never be triggered, since most likely the
> memory behind the jump_label entries will be accesable and the
> entry->key will be different than the expected value.
> 
> 
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> ---
>  kernel/jump_label.c |   18 +++++++++++++-----
>  1 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index 74d1c09..fa27e75 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -105,9 +105,12 @@ static int __jump_label_text_reserved(struct jump_entry *iter_start,
>  }
>  
>  static void __jump_label_update(struct jump_label_key *key,
> -		struct jump_entry *entry, int enable)
> +				struct jump_entry *entry,
> +				struct jump_entry *stop, int enable)
>  {
> -	for (; entry->key == (jump_label_t)(unsigned long)key; entry++) {
> +	for (; (entry < stop) &&
> +	      (entry->key == (jump_label_t)(unsigned long)key);
> +	      entry++) {
>  		/*
>  		 * entry->code set to 0 invalidates module init text sections
>  		 * kernel_text_address() verifies we are not in core kernel
> @@ -181,7 +184,11 @@ static void __jump_label_mod_update(struct jump_label_key *key, int enable)
>  	struct jump_label_mod *mod = key->next;
>  
>  	while (mod) {
> -		__jump_label_update(key, mod->entries, enable);
> +		struct module *m = mod->mod;
> +
> +		__jump_label_update(key, mod->entries,
> +				    m->jump_entries + m->num_jump_entries,
> +				    enable);
>  		mod = mod->next;
>  	}
>  }
> @@ -245,7 +252,8 @@ static int jump_label_add_module(struct module *mod)
>  		key->next = jlm;
>  
>  		if (jump_label_enabled(key))
> -			__jump_label_update(key, iter, JUMP_LABEL_ENABLE);
> +			__jump_label_update(key, iter, iter_stop,
> +					    JUMP_LABEL_ENABLE);
>  	}
>  
>  	return 0;
> @@ -371,7 +379,7 @@ static void jump_label_update(struct jump_label_key *key, int enable)
>  
>  	/* if there are no users, entry can be NULL */
>  	if (entry)
> -		__jump_label_update(key, entry, enable);
> +		__jump_label_update(key, entry, __stop___jump_table, enable);
>  
>  #ifdef CONFIG_MODULES
>  	__jump_label_mod_update(key, enable);
> -- 
> 1.7.1
> 

Looks good.

Acked-by: Jason Baron <jbaron@redhat.com>

Thanks,

-Jason