[ASAN] fix startup crash in dlsym for long paths since glibc 2.27

[Lekensteyn]

Summary

Error messages for dlsym used to be stored on the stack, but since
commit 2449ae7b ("ld.so: Introduce struct dl_exception") in glibc 2.27
these are now stored on the heap (and thus use the dlsym alloc pool).

Messages look like "undefined symbol: __isoc99_printf\0/path/to/a.out".
With many missing library functions and long object paths, the pool is
quickly exhausted. Implement a simple mechanism to return freed memory
to the pool (clear it in case it is used for calloc).

Fixes https://github.com/google/sanitizers/issues/957

[vitalybuka]

lib/asan/asan_malloc_linux.cc

58

Alternative, more general solution is to have some bitmap which tells if byte is allocated. And then trim the tail on each free.

[Lekensteyn]

lib/asan/asan_malloc_linux.cc

58

A bitmap before (or after) an allocation increases memory consumption (by a tiny amount). It would only be beneficial in the following pattern:

p = malloc(a); q = malloc(b);
free(q); free(p); // currently does not release "p"
// or:
//free(p); free(q); // currently does not release "p" and "q"

however as I have not observed these patterns and its implementation is more complex, I decided to take the current, simpler approach.

[delcypher]

compiler-rt/trunk/lib/asan/asan_malloc_linux.cc

53 ↗

(On Diff #151324)

Typo? s/dlsym longer/dlsym no longer/

54 ↗

(On Diff #151324)

Typo. s/use/uses/

[Lekensteyn]

Thanks for the reviews, I fixed both typos in r334719 and disabled the test due to a lit problem on Windows. I'll be looking at supporting glob patterns for commands in general or just the "cd" builtin.

Failing test: http://lab.llvm.org:8011/builders/sanitizer-windows/builds/30093

******************** TEST 'AddressSanitizer-i386-windows :: TestCases/long-object-path.cc' FAILED ********************
Exception during script execution:
Traceback (most recent call last):
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\run.py", line 202, in _execute_test_impl
    result = test.config.test_format.execute(test, lit_config)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\formats\shtest.py", line 25, in execute
    self.execute_external)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\TestRunner.py", line 1576, in executeShTest
    res = _runShTest(test, litConfig, useExternalSh, script, tmpBase)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\TestRunner.py", line 1524, in _runShTest
    res = executeScriptInternal(test, litConfig, tmpBase, script, execdir)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\TestRunner.py", line 1019, in executeScriptInternal
    exitCode, timeoutInfo = executeShCmd(cmd, shenv, results, timeout=litConfig.maxIndividualTestTime)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\TestRunner.py", line 163, in executeShCmd
    finalExitCode = _executeShCmd(cmd, shenv, results, timeoutHelper)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\TestRunner.py", line 738, in _executeShCmd
    res = _executeShCmd(cmd.rhs, shenv, results, timeoutHelper)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\TestRunner.py", line 721, in _executeShCmd
    return _executeShCmd(cmd.rhs, shenv, results, timeoutHelper)
  File "C:/b/slave/sanitizer-windows/llvm\utils\lit\lit\TestRunner.py", line 852, in _executeShCmd
    is_builtin_cmd = args[0] in builtin_commands;
TypeError: unhashable instance

Reproducible on Linux with the environment variable LIT_USE_INTERNAL_SHELL=1 set.

lib/asan/asan_malloc_linux.cc

 #include "asan_internal.h"
 #include "asan_malloc_local.h"
 #include "asan_stack.h"
 
 // ---------------------- Replacement functions ---------------- {{{1
 using namespace __asan;  // NOLINT
 
 static uptr allocated_for_dlsym;
+static uptr last_dlsym_alloc_size_in_words;
 static const uptr kDlsymAllocPoolSize = SANITIZER_RTEMS ? 4096 : 1024;
 static uptr alloc_memory_for_dlsym[kDlsymAllocPoolSize];
 
 static INLINE bool IsInDlsymAllocPool(const void *ptr) {
   uptr off = (uptr)ptr - (uptr)alloc_memory_for_dlsym;
   return off < allocated_for_dlsym * sizeof(alloc_memory_for_dlsym[0]);
 }
 
 static void *AllocateFromLocalPool(uptr size_in_bytes) {
   uptr size_in_words = RoundUpTo(size_in_bytes, kWordSize) / kWordSize;
   void *mem = (void*)&alloc_memory_for_dlsym[allocated_for_dlsym];
+  last_dlsym_alloc_size_in_words = size_in_words;
   allocated_for_dlsym += size_in_words;
   CHECK_LT(allocated_for_dlsym, kDlsymAllocPoolSize);
   return mem;
 }
 
+static void DeallocateFromLocalPool(const void *ptr) {
+  // Hack: since glibc 2.27, dlsym longer use stack-allocated memory to store
+  // error messages and instead use malloc followed by free. To avoid pool
+  // exhaustion due to long object filenames, handle that special case here.
+  uptr prev_offset = allocated_for_dlsym - last_dlsym_alloc_size_in_words;
+  void *prev_mem = (void*)&alloc_memory_for_dlsym[prev_offset];
+  if (prev_mem == ptr) {
+    REAL(memset)(prev_mem, 0, last_dlsym_alloc_size_in_words * kWordSize);
+    allocated_for_dlsym = prev_offset;
+    last_dlsym_alloc_size_in_words = 0;
+  }
+}
+
 static int PosixMemalignFromLocalPool(void **memptr, uptr alignment,
                                       uptr size_in_bytes) {
   if (UNLIKELY(!CheckPosixMemalignAlignment(alignment)))
     return errno_EINVAL;
 
   CHECK(alignment >= kWordSize);
 
   uptr addr = (uptr)&alloc_memory_for_dlsym[allocated_for_dlsym];
if (UNLIKELY(UseLocalPool())) {
     new_ptr = asan_malloc(size, &stack);
   }
   internal_memcpy(new_ptr, ptr, copy_size);
   return new_ptr;
 }
 
 INTERCEPTOR(void, free, void *ptr) {
   GET_STACK_TRACE_FREE;
-  if (UNLIKELY(IsInDlsymAllocPool(ptr)))
+  if (UNLIKELY(IsInDlsymAllocPool(ptr))) {
+    DeallocateFromLocalPool(ptr);
     return;
+  }
   asan_free(ptr, &stack, FROM_MALLOC);
 }
 
 #if SANITIZER_INTERCEPT_CFREE
 INTERCEPTOR(void, cfree, void *ptr) {
   GET_STACK_TRACE_FREE;
   if (UNLIKELY(IsInDlsymAllocPool(ptr)))
     return;

test/asan/TestCases/long-object-path.cc

+// RUN: mkdir -p %T/a-long-directory-name-to-test-allocations-for-exceptions-in-_dl_lookup_symbol_x-since-glibc-2.27
+// RUN: %clangxx_asan -g %s -o %T/long-object-path
+// RUN: %run %T/a-*/../a-*/../a-*/../a-*/../a-*/../a-*/../a-*/../a-*/../long-object-path
+
+int main(void) {
+    return 0;
+}