fix bug with elf object left with file open upon error causing Entered fatal...

fix bug with elf object left with file open upon error causing Entered fatal signal handler recursively later

Summary: fix bug with elf object left with file open upon error causing Entered fatal signal handler recursively later

Test Plan: run publisher at the limit

Reviewed By: tudorb@fb.com

Subscribers: trunkagent, chip, folly-diffs@

FB internal diff: D1743052

Tasks: 5752190

Signature: t1:1743052:1418780889:ad2ee0e6999cf417c2b9fd1ef6bc82d2086774a1

folly/experimental/symbolizer/Elf.cpp

@@ -28,6 +28,7 @@
 
 #include <folly/Conv.h>
 #include <folly/Exception.h>
+#include <folly/ScopeGuard.h>
 
 namespace folly {
 namespace symbolizer {
@@ -65,7 +66,10 @@ int ElfFile::openNoThrow(const char* name, bool readOnly, const char** msg)
     if (msg) *msg = "open";
     return kSystemError;
   }
-
+  // Always close fd and unmap in case of failure along the way to avoid
+  // check failure above if we leave fd != -1 and the object is recycled
+  // like it is inside SignalSafeElfCache
+  ScopeGuard guard = makeGuard([&]{ reset(); });
   struct stat st;
   int r = fstat(fd_, &st);
   if (r == -1) {
@@ -87,12 +91,12 @@ int ElfFile::openNoThrow(const char* name, bool readOnly, const char** msg)
     errno = EINVAL;
     return kInvalidElfFile;
   }
-
+  guard.dismiss();
   return kSuccess;
 }
 
 ElfFile::~ElfFile() {
-  destroy();
+  reset();
 }
 
 ElfFile::ElfFile(ElfFile&& other) noexcept
@@ -108,7 +112,7 @@ ElfFile::ElfFile(ElfFile&& other) noexcept
 
 ElfFile& ElfFile::operator=(ElfFile&& other) {
   assert(this != &other);
-  destroy();
+  reset();
 
   fd_ = other.fd_;
   file_ = other.file_;
@@ -123,13 +127,15 @@ ElfFile& ElfFile::operator=(ElfFile&& other) {
   return *this;
 }
 
-void ElfFile::destroy() {
+void ElfFile::reset() {
   if (file_ != MAP_FAILED) {
     munmap(file_, length_);
+    file_ = static_cast<char*>(MAP_FAILED);
   }
 
   if (fd_ != -1) {
     close(fd_);
+    fd_ = -1;
   }
 }
 

folly/experimental/symbolizer/Elf.h

@@ -193,7 +193,7 @@ class ElfFile {
 
  private:
   bool init(const char** msg);
-  void destroy();
+  void reset();
   ElfFile(const ElfFile&) = delete;
   ElfFile& operator=(const ElfFile&) = delete;