Expand LOAD segment to cover new .dynstr and .dynsym sections

This is not a robust fix, the first PT_LOAD segment is expanded
forward to cover .dynstr or .dynsym.

This is verified to fix segmentation faults in the loader when loading
programs where the .dynstr or .dynstm section gets bumped out of the
LOAD segment

Fixes: NixOS#244

Author: ehmry

src/patchelf.cc

@@ -787,6 +787,46 @@ void ElfFile<ElfFileParamNames>::writeReplacedSections(Elf_Off & curOff,
         curOff += roundUp(i->second.size(), sectionAlignment);
     }
 
+    /* Expand the LOAD segment as neccessary */
+    for (auto & i : replacedSections) {
+        std::string sectionName = i.first;
+
+        /* If this is the .dynstr or .dynsym section, then a PT_LOAD segment
+           must contain it. */
+        if (sectionName == ".dynstr" || sectionName == ".dynsym") {
+            auto const & shdr = findSectionHeader(sectionName);
+            bool loaded = false;
+            for (auto & phdr : phdrs) {
+                if (rdi(phdr.p_type) == PT_LOAD) {
+                    if (rdi(phdr.p_offset) <= rdi(shdr.sh_offset) &&
+                        rdi(shdr.sh_size) <= rdi(phdr.p_filesz)) {
+                        debug("'%s' section is loaded\n", sectionName.c_str());
+                        loaded = true;
+                        break;
+                    }
+                }
+            }
+
+            if (!loaded) {
+                debug("'%s' was moved out of a load segment…\n", sectionName.c_str());
+                for (auto & phdr : phdrs) {
+                    if (rdi(phdr.p_type) == PT_LOAD) {
+                        if (rdi(shdr.sh_offset) < rdi(phdr.p_offset)) {
+                            Elf64_Xword gap = rdi(phdr.p_offset) - rdi(shdr.sh_offset);
+                            debug("grow PT_LOAD segment by 0x%x to cover '%s'\n",
+                                gap, sectionName.c_str());
+                            wri(phdr.p_filesz, rdi(phdr.p_filesz) + gap);
+                            wri(phdr.p_memsz, rdi(phdr.p_memsz) + gap);
+                            phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr;
+                            phdr.p_offset = shdr.sh_offset;
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+    }
+
     replacedSections.clear();
 }