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Commit 3a14004c authored by Christopher Ferris's avatar Christopher Ferris
Browse files

Fix race condition updating local map data. 

If the underlying local map changes, it's possible for multiple
threads to try and modify the map data associated with the UnwindLocalMap
object. Add a lock when generating the local map to avoid this problem.

In addition, add a read lock whenever any caller gets the maps iterator.
Updated all iterator callers to make this lock.

Bug: 29387050
Change-Id: Ie34822c3d8fd3bdb3dd126aeeb399969c36508c1
parent 4d346537

debuggerd/tombstone.cpp

+1 −0
Original line number Diff line number Diff line
@@ -368,6 +368,7 @@ static void dump_all_maps(Backtrace* backtrace, BacktraceMap* map, log_t* log, p 
    ALOGE("Cannot get siginfo for %d: %s\n", tid, strerror(errno));

  }



  ScopedBacktraceMapIteratorLock lock(map);

  _LOG(log, logtype::MAPS, "\n");

  if (!print_fault_address_marker) {

    _LOG(log, logtype::MAPS, "memory map:\n");

include/backtrace/BacktraceMap.h

+20 −0
Original line number Diff line number Diff line
@@ -71,6 +71,12 @@ public: 
  bool IsWritable(uintptr_t pc) { return GetFlags(pc) & PROT_WRITE; }

  bool IsExecutable(uintptr_t pc) { return GetFlags(pc) & PROT_EXEC; }



  // In order to use the iterators on this object, a caller must

  // call the LockIterator and UnlockIterator function to guarantee

  // that the data does not change while it's being used.

  virtual void LockIterator() {}

  virtual void UnlockIterator() {}



  typedef std::deque<backtrace_map_t>::iterator iterator;

  iterator begin() { return maps_.begin(); }

  iterator end() { return maps_.end(); }
@@ -102,4 +108,18 @@ protected: 
  pid_t pid_;

};



class ScopedBacktraceMapIteratorLock {

public:

  explicit ScopedBacktraceMapIteratorLock(BacktraceMap* map) : map_(map) {

    map->LockIterator();

  }



  ~ScopedBacktraceMapIteratorLock() {

    map_->UnlockIterator();

  }



private:

  BacktraceMap* map_;

};



#endif // _BACKTRACE_BACKTRACE_MAP_H

libbacktrace/BacktraceMap.cpp

+2 −2
Original line number Diff line number Diff line
@@ -36,8 +36,8 @@ BacktraceMap::~BacktraceMap() { 
}



void BacktraceMap::FillIn(uintptr_t addr, backtrace_map_t* map) {

  for (BacktraceMap::const_iterator it = begin();

       it != end(); ++it) {

  ScopedBacktraceMapIteratorLock lock(this);

  for (BacktraceMap::const_iterator it = begin(); it != end(); ++it) {

    if (addr >= it->start && addr < it->end) {

      *map = *it;

      return;

libbacktrace/UnwindMap.cpp

+15 −3
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
 * limitations under the License.

 */



#include <pthread.h>

#include <stdint.h>

#include <stdlib.h>

#include <sys/types.h>
@@ -72,6 +73,7 @@ bool UnwindMapRemote::Build() { 
}



UnwindMapLocal::UnwindMapLocal() : UnwindMap(getpid()), map_created_(false) {

  pthread_rwlock_init(&map_lock_, nullptr);

}



UnwindMapLocal::~UnwindMapLocal() {
@@ -82,9 +84,14 @@ UnwindMapLocal::~UnwindMapLocal() { 
}



bool UnwindMapLocal::GenerateMap() {

  // Lock so that multiple threads cannot modify the maps data at the

  // same time.

  pthread_rwlock_wrlock(&map_lock_);



  // It's possible for the map to be regenerated while this loop is occurring.

  // If that happens, get the map again, but only try at most three times

  // before giving up.

  bool generated = false;

  for (int i = 0; i < 3; i++) {

    maps_.clear();
@@ -110,12 +117,17 @@ bool UnwindMapLocal::GenerateMap() { 
    }

    // Check to see if the map changed while getting the data.

    if (ret != -UNW_EINVAL) {

      return true;

      generated = true;

      break;

    }

  }



  pthread_rwlock_unlock(&map_lock_);



  if (!generated) {

    BACK_LOGW("Unable to generate the map.");

  return false;

  }

  return generated;

}



bool UnwindMapLocal::Build() {

libbacktrace/UnwindMap.h

+6 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#ifndef _LIBBACKTRACE_UNWIND_MAP_H

#define _LIBBACKTRACE_UNWIND_MAP_H



#include <pthread.h>

#include <stdint.h>

#include <sys/types.h>
@@ -56,10 +57,15 @@ public: 


  void FillIn(uintptr_t addr, backtrace_map_t* map) override;



  void LockIterator() override { pthread_rwlock_rdlock(&map_lock_); }

  void UnlockIterator() override { pthread_rwlock_unlock(&map_lock_); }



private:

  bool GenerateMap();



  bool map_created_;



  pthread_rwlock_t map_lock_;

};



#endif // _LIBBACKTRACE_UNWIND_MAP_H