Re: callchain map refcounting fixes was Re: [PATCH perf/core] perf script: fix a use after free crash.

[Namhyung Kim <namhyung@kernel.org>]

Hi Arnaldo and Krister,

On Wed, Oct 05, 2016 at 08:45:24AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sat, Oct 01, 2016 at 08:13:36PM -0700, Krister Johansen escreveu:
> > If dso__load_kcore frees all of the existing maps, but one has already
> > been attached to a callchain cursor node, then we can get a SIGSEGV in
> > any function that happens to try to use this cursor with the invalid
> > map.  Use the existing map refcount mechanism to forestall cleanup of a
> > map until the cursor iterates past the node.
> 
> Seems ok, thanks for working on this! Can you provide a test case that
> causes the SEGV so that I can, in addition to reviewing your changes and
> auditing the code to check if all cases ara plugged, to reproduce the
> problem?
> 
> Frédéric, Namhyung, Ack?
> 
> Masami, is this a case that your refcount validator can catch?
> 
> - Arnaldo
>  
> > Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
> > ---
> >  tools/perf/util/callchain.c | 12 ++++++++++--
> >  tools/perf/util/callchain.h | 20 ++++++++++++++++++++
> >  tools/perf/util/hist.c      |  4 ++++
> >  3 files changed, 34 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> > index 07fd30b..15c89b2 100644
> > --- a/tools/perf/util/callchain.c
> > +++ b/tools/perf/util/callchain.c
> > @@ -439,7 +439,7 @@ fill_node(struct callchain_node *node, struct callchain_cursor *cursor)
> >  		}
> >  		call->ip = cursor_node->ip;
> >  		call->ms.sym = cursor_node->sym;
> > -		call->ms.map = cursor_node->map;
> > +		call->ms.map = map__get(cursor_node->map);
> >  		list_add_tail(&call->list, &node->val);
> >  
> >  		callchain_cursor_advance(cursor);
> > @@ -464,6 +464,7 @@ add_child(struct callchain_node *parent,
> >  
> >  		list_for_each_entry_safe(call, tmp, &new->val, list) {
> >  			list_del(&call->list);
> > +			map__zput(call->ms.map);
> >  			free(call);
> >  		}
> >  		free(new);
> > @@ -732,6 +733,7 @@ merge_chain_branch(struct callchain_cursor *cursor,
> >  		callchain_cursor_append(cursor, list->ip,
> >  					list->ms.map, list->ms.sym);
> >  		list_del(&list->list);
> > +		map__zput(list->ms.map);
> >  		free(list);
> >  	}
> >  
> > @@ -780,7 +782,8 @@ int callchain_cursor_append(struct callchain_cursor *cursor,
> >  	}
> >  
> >  	node->ip = ip;
> > -	node->map = map;
> > +	map__zput(node->map);
> > +	node->map = map__get(map);
> >  	node->sym = sym;
> >  
> >  	cursor->nr++;
> > @@ -830,6 +833,8 @@ int fill_callchain_info(struct addr_location *al, struct callchain_cursor_node *
> >  			goto out;
> >  	}
> >  
> > +	map__get(al->map);
> > +
> >  	if (al->map->groups == &al->machine->kmaps) {
> >  		if (machine__is_host(al->machine)) {
> >  			al->cpumode = PERF_RECORD_MISC_KERNEL;
> > @@ -947,11 +952,13 @@ static void free_callchain_node(struct callchain_node *node)
> >  
> >  	list_for_each_entry_safe(list, tmp, &node->parent_val, list) {
> >  		list_del(&list->list);
> > +		map__zput(list->ms.map);
> >  		free(list);
> >  	}
> >  
> >  	list_for_each_entry_safe(list, tmp, &node->val, list) {
> >  		list_del(&list->list);
> > +		map__zput(list->ms.map);
> >  		free(list);
> >  	}
> >  
> > @@ -1035,6 +1042,7 @@ int callchain_node__make_parent_list(struct callchain_node *node)
> >  out:
> >  	list_for_each_entry_safe(chain, new, &head, list) {
> >  		list_del(&chain->list);
> > +		map__zput(chain->ms.map);

I think you need to grab the refcnt in the "while (parent)" loop above.


> >  		free(chain);
> >  	}
> >  	return -ENOMEM;
> > diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
> > index 13e7554..0d944ef 100644
> > --- a/tools/perf/util/callchain.h
> > +++ b/tools/perf/util/callchain.h
> > @@ -5,6 +5,7 @@
> >  #include <linux/list.h>
> >  #include <linux/rbtree.h>
> >  #include "event.h"
> > +#include "map.h"
> >  #include "symbol.h"
> >  
> >  #define HELP_PAD "\t\t\t\t"
> > @@ -178,8 +179,13 @@ int callchain_merge(struct callchain_cursor *cursor,
> >   */
> >  static inline void callchain_cursor_reset(struct callchain_cursor *cursor)
> >  {
> > +	struct callchain_cursor_node *node;
> > +
> >  	cursor->nr = 0;
> >  	cursor->last = &cursor->first;
> > +
> > +	for (node = cursor->first; node != NULL; node = node->next)
> > +		map__zput(node->map);
> >  }
> >  
> >  int callchain_cursor_append(struct callchain_cursor *cursor, u64 ip,
> > @@ -238,12 +244,26 @@ int perf_callchain_config(const char *var, const char *value);
> >  static inline void callchain_cursor_snapshot(struct callchain_cursor *dest,
> >  					     struct callchain_cursor *src)
> >  {
> > +	struct callchain_cursor_node *node;
> > +
> >  	*dest = *src;
> >  
> >  	dest->first = src->curr;
> >  	dest->nr -= src->pos;
> > +
> > +	for (node = dest->first; node != NULL; node = node->next)
> > +		map__get(node->map);
> >  }
> >  
> > +static inline void callchain_cursor_snapshot_rele(struct callchain_cursor *curs)
> > +{
> > +	struct callchain_cursor_node *node;
> > +
> > +	for (node = curs->first; node != NULL; node = node->next)
> > +		map__put(node->map);
> > +}
> > +
> > +
> >  #ifdef HAVE_SKIP_CALLCHAIN_IDX
> >  int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain);
> >  #else
> > diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
> > index b02992e..f8335e8 100644
> > --- a/tools/perf/util/hist.c
> > +++ b/tools/perf/util/hist.c
> > @@ -1,6 +1,7 @@
> >  #include "util.h"
> >  #include "build-id.h"
> >  #include "hist.h"
> > +#include "map.h"
> >  #include "session.h"
> >  #include "sort.h"
> >  #include "evlist.h"
> > @@ -970,6 +971,8 @@ iter_add_next_cumulative_entry(struct hist_entry_iter *iter,
> >  
> >  	if (symbol_conf.use_callchain)
> >  		callchain_append(he->callchain, &cursor, sample->period);
> > +	/* Cleanup temporary cursor. */
> > +	callchain_cursor_snapshot_rele(&cursor);

This callchain shotshot is used in a short period of time, and it's
guaranteed that the maps in callchains will not freed due to refcnt in
the orignal callchain cursor.  So I think we can skip to get/put
refcnt on the snapshot cursor.  Also "rele" seems not a good name..


> >  	return 0;
> >  }
> >  
> > @@ -979,6 +982,7 @@ iter_finish_cumulative_entry(struct hist_entry_iter *iter,
> >  {
> >  	zfree(&iter->priv);
> >  	iter->he = NULL;
> > +	map__zput(al->map);

What is this needed?  Why other places like iter_finish_normal_entry
isn't?


> >  
> >  	return 0;
> >  }
> > -- 
> > 2.7.4