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Patch init field trial dictionary #208

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Patch init field trial dictionary #208

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18 changes: 10 additions & 8 deletions sdk/objc/api/peerconnection/RTCFieldTrials.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@

#import <os/lock.h>
#include <memory>
#include <vector>
#import "base/RTCLogging.h"

#include "system_wrappers/include/field_trial.h"
Expand All @@ -26,8 +27,10 @@
NSString *const RTC_CONSTANT_TYPE(RTCFieldTrialEnabledValue) = @"Enabled";

// InitFieldTrialsFromString stores the char*, so the char array must outlive
// the application.
// the application. Keep all historical strings alive to avoid races where
// other threads read the previous pointer while we are updating it.
static char *gFieldTrialInitString = nullptr;
static std::vector<std::unique_ptr<char[]>> gFieldTrialStorage;
static os_unfair_lock fieldTrialLock = OS_UNFAIR_LOCK_INIT;

void RTC_OBJC_TYPE(RTCInitFieldTrialDictionary)(NSDictionary<NSString *, NSString *> *fieldTrials) {
Expand All @@ -50,13 +53,8 @@ void RTC_OBJC_TYPE(RTCInitFieldTrialDictionary)(NSDictionary<NSString *, NSStrin

// Locking before modifying global variable
os_unfair_lock_lock(&fieldTrialLock);
if (gFieldTrialInitString != nullptr) {
delete[] gFieldTrialInitString;
gFieldTrialInitString = nullptr;
}

gFieldTrialInitString = new char[len];
bool success = [fieldTrialInitString getCString:gFieldTrialInitString
auto newString = std::make_unique<char[]>(len);
bool success = [fieldTrialInitString getCString:newString.get()
maxLength:len
encoding:NSUTF8StringEncoding];
if (!success) {
Expand All @@ -65,6 +63,10 @@ void RTC_OBJC_TYPE(RTCInitFieldTrialDictionary)(NSDictionary<NSString *, NSStrin
return;
}

// Keep the buffer alive for the remainder of the process lifetime to avoid
// use-after-free if other threads are still reading the old pointer.
gFieldTrialInitString = newString.get();
webrtc::field_trial::InitFieldTrialsFromString(gFieldTrialInitString);
gFieldTrialStorage.emplace_back(std::move(newString));
os_unfair_lock_unlock(&fieldTrialLock);
}