[sanitizer_common] Fix readlink error handling in sanitizer_procmaps_solaris.cpp

[ro]

Summary

As Rich Lowe pointed out in Bug 52371, the Solaris version of MemoryMappingLayout::Next completely failed to handle readlink errors or properly
NUL-terminate the result.

This patch fixes this. Originally provided in the PR with slight formatting changes.

Tested on amd64-pc-solaris2.11.

I'm uncertain how to properly attribute the patch on commit, though.

[vitalybuka]

compiler-rt/lib/sanitizer_common/sanitizer_procmaps_solaris.cpp

58–66

Can you check if sanitizer_common/tests/sanitizer_procmaps_test.cc can be enabled for Solaris and does it trigger this error?

[vitalybuka]

compiler-rt/lib/sanitizer_common/sanitizer_procmaps_solaris.cpp

58–66

Would you like to fix usage of internal_readlink in ReadBinaryName?
it's called only for zero-initialized global buffer so, there is very low probability to hit error, but it's incorrect in general.

[ro]

compiler-rt/lib/sanitizer_common/sanitizer_procmaps_solaris.cpp

58–66

The test already runs and PASSes on Solaris/i386 and x86_64.
sanitizer_common tests are not yet enabled on sparc, though (D91608).

If my suspicion mentioned in the PR is true, the random failures
only seen on the Solaris/amd64 buildbot once in a while would
be gone for this patch.

58–66

Will do in a separate patch.

compiler-rt/lib/sanitizer_common/sanitizer_procmaps_solaris.cpp

bool MemoryMappingLayout::Next(MemoryMappedSegment *segment) {
   if ((xmapentry->pr_mflags & MA_EXEC) != 0)
     segment->protection |= kProtectionExecute;
 
   if (segment->filename != NULL && segment->filename_size > 0) {
     char proc_path[PATH_MAX + 1];
 
     internal_snprintf(proc_path, sizeof(proc_path), "/proc/self/path/%s",
                       xmapentry->pr_mapname);
-    internal_readlink(proc_path, segment->filename, segment->filename_size);
+    ssize_t sz = internal_readlink(proc_path, segment->filename,
+                                   segment->filename_size - 1);
+
+    // If readlink failed, the map is anonymous.
+    if (sz == -1) {
+      segment->filename[0] = '\0';
+    } else if ((size_t)sz < segment->filename_size)
+      // readlink doesn't NUL-terminate.
+      segment->filename[sz] = '\0';
   }
 
   data_.current += sizeof(prxmap_t);
 
   return true;
 }
 
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_SOLARIS