Fix shared memory corruption and ELF parsing infinite loop

- Move memset inside shm_exists check to avoid corrupting existing
  shared memory during re-initialization (fixes daemon attach failure)
- Add check for zero aligned sizes in ELF note parsing to prevent
  infinite loop on 32-bit systems with malformed notes

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: mujacica

src/backends/native/minidump/sentry_minidump_linux.c

@@ -840,9 +840,13 @@ extract_elf_build_id(const char *elf_path, uint8_t *build_id, size_t max_len)
                     ptr += sizeof(*nhdr);
 
                     // Use aligned sizes in bounds check since pointer advances
-                    // by aligned amounts
+                    // by aligned amounts. Also check for zero advancement to
+                    // prevent infinite loop on malformed notes (e.g., overflow
+                    // on 32-bit when n_namesz/n_descsz are near UINT32_MAX)
                     size_t aligned_namesz = ((nhdr->n_namesz + 3) & ~3);
                     size_t aligned_descsz = ((nhdr->n_descsz + 3) & ~3);
+                    if (aligned_namesz == 0 && aligned_descsz == 0)
+                        break; // Prevent infinite loop
                     if (ptr + aligned_namesz + aligned_descsz > end)
                         break;
 

src/backends/native/sentry_crash_ipc.c

@@ -118,8 +118,11 @@ sentry__crash_ipc_init_app(sem_t *init_sem)
         return NULL;
     }
 
-    // Zero out shared memory to ensure clean state
-    memset(ipc->shmem, 0, SENTRY_CRASH_SHM_SIZE);
+    // Zero out shared memory only when first created to ensure clean state
+    // Don't zero existing memory to avoid corrupting state set by other threads
+    if (!shm_exists) {
+        memset(ipc->shmem, 0, SENTRY_CRASH_SHM_SIZE);
+    }
 
     // Create eventfd for crash notifications
     ipc->notify_fd = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);