[PATCH v10 07/20] perf vdso: Fix unlocked __dsos__add() and race in __machine__addnew_vdso()

[Ian Rogers <irogers@google.com>]

__machine__addnew_vdso() called __dsos__add(&machine->dsos, dso) without
holding machine->dsos.lock, and machine__findnew_vdso() and
__machine__findnew_compat() initialized machine->vdso_info and created
temporary VDSO files without synchronization. Acquire
machine->dsos.lock in write mode across machine->vdso_info
initialization, duplicate checking via __dsos__find(), temporary file
creation, dso__set_long_name(), and __dsos__add().

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/dsos.c |  8 ++++++-
 tools/perf/util/dsos.h |  2 ++
 tools/perf/util/vdso.c | 52 +++++++++++++++++++++++++++---------------
 3 files changed, 42 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/dsos.c b/tools/perf/util/dsos.c
index a2cd37bd1660..1574c8885d78 100644
--- a/tools/perf/util/dsos.c
+++ b/tools/perf/util/dsos.c
@@ -284,12 +284,18 @@ static struct dso *__dsos__find_id(struct dsos *dsos, const char *name, const st
 	return res;
 }
 
+struct dso *__dsos__find(struct dsos *dsos, const char *name, bool cmp_short, bool write_locked)
+	__must_hold_shared(&dsos->lock)
+{
+	return __dsos__find_id(dsos, name, &dso_id_empty, cmp_short, write_locked);
+}
+
 struct dso *dsos__find(struct dsos *dsos, const char *name, bool cmp_short)
 {
 	struct dso *res;
 
 	down_read(&dsos->lock);
-	res = __dsos__find_id(dsos, name, &dso_id_empty, cmp_short, /*write_locked=*/false);
+	res = __dsos__find(dsos, name, cmp_short, /*write_locked=*/false);
 	up_read(&dsos->lock);
 	return res;
 }
diff --git a/tools/perf/util/dsos.h b/tools/perf/util/dsos.h
index a26774950866..dbd06f420753 100644
--- a/tools/perf/util/dsos.h
+++ b/tools/perf/util/dsos.h
@@ -30,6 +30,8 @@ void dsos__exit(struct dsos *dsos);
 
 int __dsos__add(struct dsos *dsos, struct dso *dso);
 int dsos__add(struct dsos *dsos, struct dso *dso);
+struct dso *__dsos__find(struct dsos *dsos, const char *name, bool cmp_short, bool write_locked)
+	__must_hold_shared(&dsos->lock);
 struct dso *dsos__find(struct dsos *dsos, const char *name, bool cmp_short);
 
 struct dso *dsos__findnew_id(struct dsos *dsos, const char *name, const struct dso_id *id);
diff --git a/tools/perf/util/vdso.c b/tools/perf/util/vdso.c
index c12f5d8c4bf6..93828e660672 100644
--- a/tools/perf/util/vdso.c
+++ b/tools/perf/util/vdso.c
@@ -131,8 +131,13 @@ static struct dso *__machine__addnew_vdso(struct machine *machine, const char *s
 
 	dso = dso__new(short_name);
 	if (dso != NULL) {
-		__dsos__add(&machine->dsos, dso);
+		/*
+		 * Set the long name before adding to machine->dsos so that
+		 * __dsos__add() inserts it in sorted order without needing to
+		 * re-take machine->dsos.lock.
+		 */
 		dso__set_long_name(dso, long_name, false);
+		__dsos__add(&machine->dsos, dso);
 	}
 
 	return dso;
@@ -250,15 +255,19 @@ static struct dso *__machine__findnew_compat(struct machine *machine,
 	const char *file_name;
 	struct dso *dso;
 
-	dso = dsos__find(&machine->dsos, vdso_file->dso_name, true);
+	down_write(&machine->dsos.lock);
+	dso = __dsos__find(&machine->dsos, vdso_file->dso_name, true, /*write_locked=*/true);
 	if (dso)
-		return dso;
+		goto out_unlock;
 
 	file_name = vdso__get_compat_file(vdso_file);
 	if (!file_name)
-		return NULL;
+		goto out_unlock;
 
-	return __machine__addnew_vdso(machine, vdso_file->dso_name, file_name);
+	dso = __machine__addnew_vdso(machine, vdso_file->dso_name, file_name);
+out_unlock:
+	up_write(&machine->dsos.lock);
+	return dso;
 }
 
 static int __machine__findnew_vdso_compat(struct machine *machine,
@@ -332,33 +341,38 @@ struct dso *machine__findnew_vdso(struct machine *machine,
 {
 	struct vdso_info *vdso_info;
 	struct dso *dso = NULL;
-	char *file;
+	const char *file;
 
+	dso = machine__find_vdso(machine, thread);
+	if (dso)
+		return dso;
+
+	down_write(&machine->dsos.lock);
 	if (!machine->vdso_info)
 		machine->vdso_info = vdso_info__new();
 
 	vdso_info = machine->vdso_info;
-	if (!vdso_info)
+	if (!vdso_info) {
+		up_write(&machine->dsos.lock);
 		return NULL;
-
-	dso = machine__find_vdso(machine, thread);
-	if (dso)
-		return dso;
+	}
 
 #if BITS_PER_LONG == 64
+	up_write(&machine->dsos.lock);
 	if (__machine__findnew_vdso_compat(machine, thread, vdso_info, &dso))
 		return dso;
+	down_write(&machine->dsos.lock);
 #endif
 
-	dso = dsos__find(&machine->dsos, DSO__NAME_VDSO, true);
-	if (dso)
-		return dso;
-
-	file = get_file(&vdso_info->vdso);
-	if (!file)
-		return NULL;
+	dso = __dsos__find(&machine->dsos, DSO__NAME_VDSO, true, /*write_locked=*/true);
+	if (!dso) {
+		file = get_file(&vdso_info->vdso);
+		if (file)
+			dso = __machine__addnew_vdso(machine, DSO__NAME_VDSO, file);
+	}
+	up_write(&machine->dsos.lock);
 
-	return __machine__addnew_vdso(machine, DSO__NAME_VDSO, file);
+	return dso;
 }
 
 bool dso__is_vdso(struct dso *dso)
-- 
2.56.0.455.g6c5a503b38-goog