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

[Jiri Olsa <jolsa@redhat.com>]

hi,
any feedback?

thanks,
jirka

On Tue, May 10, 2011 at 10:30:45AM -0400, Jason Baron wrote:
> 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