[PATCH perf/core] perf script: fix a use after free crash.

[Krister Johansen]

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.

Signed-off-by: Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>
---
 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);
 		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);
 	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);
 
 	return 0;
 }
-- 
2.7.4