diff --git a/debuggerd/debuggerd.cpp b/debuggerd/debuggerd.cpp
index a4e9cae..c352aeb 100644
--- a/debuggerd/debuggerd.cpp
+++ b/debuggerd/debuggerd.cpp
@@ -182,6 +182,16 @@
    return allowed;
 }
 
+static bool pid_contains_tid(pid_t pid, pid_t tid) {
+  char task_path[PATH_MAX];
+  if (snprintf(task_path, PATH_MAX, "/proc/%d/task/%d", pid, tid) >= PATH_MAX) {
+    ALOGE("debuggerd: task path overflow (pid = %d, tid = %d)\n", pid, tid);
+    exit(1);
+  }
+
+  return access(task_path, F_OK) == 0;
+}
+
 static int read_request(int fd, debugger_request_t* out_request) {
   ucred cr;
   socklen_t len = sizeof(cr);
@@ -226,16 +236,13 @@
 
   if (msg.action == DEBUGGER_ACTION_CRASH) {
     // Ensure that the tid reported by the crashing process is valid.
-    char buf[64];
-    struct stat s;
-    snprintf(buf, sizeof buf, "/proc/%d/task/%d", out_request->pid, out_request->tid);
-    if (stat(buf, &s)) {
-      ALOGE("tid %d does not exist in pid %d. ignoring debug request\n",
-          out_request->tid, out_request->pid);
+    // This check needs to happen again after ptracing the requested thread to prevent a race.
+    if (!pid_contains_tid(out_request->pid, out_request->tid)) {
+      ALOGE("tid %d does not exist in pid %d. ignoring debug request\n", out_request->tid,
+            out_request->pid);
       return -1;
     }
-  } else if (cr.uid == 0
-            || (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
+  } else if (cr.uid == 0 || (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
     // Only root or system can ask us to attach to any process and dump it explicitly.
     // However, system is only allowed to collect backtraces but cannot dump tombstones.
     status = get_process_info(out_request->tid, &out_request->pid,
@@ -412,10 +419,31 @@
 }
 #endif
 
-static void ptrace_siblings(pid_t pid, pid_t main_tid, std::set<pid_t>& tids) {
-  char task_path[64];
+// Attach to a thread, and verify that it's still a member of the given process
+static bool ptrace_attach_thread(pid_t pid, pid_t tid) {
+  if (ptrace(PTRACE_ATTACH, tid, 0, 0) != 0) {
+    return false;
+  }
 
-  snprintf(task_path, sizeof(task_path), "/proc/%d/task", pid);
+  // Make sure that the task we attached to is actually part of the pid we're dumping.
+  if (!pid_contains_tid(pid, tid)) {
+    if (ptrace(PTRACE_DETACH, tid, 0, 0) != 0) {
+      ALOGE("debuggerd: failed to detach from thread '%d'", tid);
+      exit(1);
+    }
+    return false;
+  }
+
+  return true;
+}
+
+static void ptrace_siblings(pid_t pid, pid_t main_tid, std::set<pid_t>& tids) {
+  char task_path[PATH_MAX];
+
+  if (snprintf(task_path, PATH_MAX, "/proc/%d/task", pid) >= PATH_MAX) {
+    ALOGE("debuggerd: task path overflow (pid = %d)\n", pid);
+    abort();
+  }
 
   std::unique_ptr<DIR, int (*)(DIR*)> d(opendir(task_path), closedir);
 
@@ -442,7 +470,7 @@
       continue;
     }
 
-    if (ptrace(PTRACE_ATTACH, tid, 0, 0) < 0) {
+    if (!ptrace_attach_thread(pid, tid)) {
       ALOGE("debuggerd: ptrace attach to %d failed: %s", tid, strerror(errno));
       continue;
     }
@@ -567,11 +595,33 @@
   // debugger_signal_handler().
 
   // Attach to the target process.
-  if (ptrace(PTRACE_ATTACH, request.tid, 0, 0) != 0) {
+  if (!ptrace_attach_thread(request.pid, request.tid)) {
     ALOGE("debuggerd: ptrace attach failed: %s", strerror(errno));
     exit(1);
   }
 
+  // DEBUGGER_ACTION_CRASH requests can come from arbitrary processes and the tid field in the
+  // request is sent from the other side. If an attacker can cause a process to be spawned with the
+  // pid of their process, they could trick debuggerd into dumping that process by exiting after
+  // sending the request. Validate the trusted request.uid/gid to defend against this.
+  if (request.action == DEBUGGER_ACTION_CRASH) {
+    pid_t pid;
+    uid_t uid;
+    gid_t gid;
+    if (get_process_info(request.tid, &pid, &uid, &gid) != 0) {
+      ALOGE("debuggerd: failed to get process info for tid '%d'", request.tid);
+      exit(1);
+    }
+
+    if (pid != request.pid || uid != request.uid || gid != request.gid) {
+      ALOGE(
+        "debuggerd: attached task %d does not match request: "
+        "expected pid=%d,uid=%d,gid=%d, actual pid=%d,uid=%d,gid=%d",
+        request.tid, request.pid, request.uid, request.gid, pid, uid, gid);
+      exit(1);
+    }
+  }
+
   // Don't attach to the sibling threads if we want to attach gdb.
   // Supposedly, it makes the process less reliable.
   bool attach_gdb = should_attach_gdb(request);
diff --git a/include/utils/Unicode.h b/include/utils/Unicode.h
index a006082..cddbab4 100644
--- a/include/utils/Unicode.h
+++ b/include/utils/Unicode.h
@@ -88,7 +88,7 @@
  * "dst" becomes \xE3\x81\x82\xE3\x81\x84
  * (note that "dst" is NOT null-terminated, like strncpy)
  */
-void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst);
+void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst, size_t dst_len);
 
 /**
  * Returns the unicode value at "index".
@@ -110,7 +110,7 @@
  * enough to fit the UTF-16 as measured by utf16_to_utf8_length with an added
  * NULL terminator.
  */
-void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst);
+void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst, size_t dst_len);
 
 /**
  * Returns the length of "src" when "src" is valid UTF-8 string.
diff --git a/libutils/String8.cpp b/libutils/String8.cpp
index ad45282..cacaf91 100644
--- a/libutils/String8.cpp
+++ b/libutils/String8.cpp
@@ -104,20 +104,21 @@
 {
     if (len == 0) return getEmptyString();
 
-    const ssize_t bytes = utf16_to_utf8_length(in, len);
-    if (bytes < 0) {
+     // Allow for closing '\0'
+    const ssize_t resultStrLen = utf16_to_utf8_length(in, len) + 1;
+    if (resultStrLen < 1) {
         return getEmptyString();
     }
 
-    SharedBuffer* buf = SharedBuffer::alloc(bytes+1);
+    SharedBuffer* buf = SharedBuffer::alloc(resultStrLen);
     ALOG_ASSERT(buf, "Unable to allocate shared buffer");
     if (!buf) {
         return getEmptyString();
     }
 
-    char* str = (char*)buf->data();
-    utf16_to_utf8(in, len, str);
-    return str;
+    char* resultStr = (char*)buf->data();
+    utf16_to_utf8(in, len, resultStr, resultStrLen);
+    return resultStr;
 }
 
 static char* allocFromUTF32(const char32_t* in, size_t len)
@@ -126,21 +127,21 @@
         return getEmptyString();
     }
 
-    const ssize_t bytes = utf32_to_utf8_length(in, len);
-    if (bytes < 0) {
+    const ssize_t resultStrLen = utf32_to_utf8_length(in, len) + 1;
+    if (resultStrLen < 1) {
         return getEmptyString();
     }
 
-    SharedBuffer* buf = SharedBuffer::alloc(bytes+1);
+    SharedBuffer* buf = SharedBuffer::alloc(resultStrLen);
     ALOG_ASSERT(buf, "Unable to allocate shared buffer");
     if (!buf) {
         return getEmptyString();
     }
 
-    char* str = (char*) buf->data();
-    utf32_to_utf8(in, len, str);
+    char* resultStr = (char*) buf->data();
+    utf32_to_utf8(in, len, resultStr, resultStrLen);
 
-    return str;
+    return resultStr;
 }
 
 // ---------------------------------------------------------------------------
diff --git a/libutils/Unicode.cpp b/libutils/Unicode.cpp
index f1f8bc9..ba084f6 100644
--- a/libutils/Unicode.cpp
+++ b/libutils/Unicode.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <log/log.h>
 #include <utils/Unicode.h>
 
 #include <stddef.h>
@@ -182,7 +183,7 @@
     return ret;
 }
 
-void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst)
+void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst, size_t dst_len)
 {
     if (src == NULL || src_len == 0 || dst == NULL) {
         return;
@@ -193,9 +194,12 @@
     char *cur = dst;
     while (cur_utf32 < end_utf32) {
         size_t len = utf32_codepoint_utf8_length(*cur_utf32);
+        LOG_ALWAYS_FATAL_IF(dst_len < len, "%zu < %zu", dst_len, len);
         utf32_codepoint_to_utf8((uint8_t *)cur, *cur_utf32++, len);
         cur += len;
+        dst_len -= len;
     }
+    LOG_ALWAYS_FATAL_IF(dst_len < 1, "dst_len < 1: %zu < 1", dst_len);
     *cur = '\0';
 }
 
@@ -348,7 +352,7 @@
            : 0);
 }
 
-void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst)
+void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst, size_t dst_len)
 {
     if (src == NULL || src_len == 0 || dst == NULL) {
         return;
@@ -369,9 +373,12 @@
             utf32 = (char32_t) *cur_utf16++;
         }
         const size_t len = utf32_codepoint_utf8_length(utf32);
+        LOG_ALWAYS_FATAL_IF(dst_len < len, "%zu < %zu", dst_len, len);
         utf32_codepoint_to_utf8((uint8_t*)cur, utf32, len);
         cur += len;
+        dst_len -= len;
     }
+    LOG_ALWAYS_FATAL_IF(dst_len < 1, "%zu < 1", dst_len);
     *cur = '\0';
 }
 
@@ -432,10 +439,10 @@
     const char16_t* const end = src + src_len;
     while (src < end) {
         if ((*src & 0xFC00) == 0xD800 && (src + 1) < end
-                && (*++src & 0xFC00) == 0xDC00) {
+                && (*(src + 1) & 0xFC00) == 0xDC00) {
             // surrogate pairs are always 4 bytes.
             ret += 4;
-            src++;
+            src += 2;
         } else {
             ret += utf32_codepoint_utf8_length((char32_t) *src++);
         }
diff --git a/libutils/tests/String8_test.cpp b/libutils/tests/String8_test.cpp
index 01e64f6..3947a5f 100644
--- a/libutils/tests/String8_test.cpp
+++ b/libutils/tests/String8_test.cpp
@@ -17,6 +17,7 @@
 #define LOG_TAG "String8_test"
 #include <utils/Log.h>
 #include <utils/String8.h>
+#include <utils/String16.h>
 
 #include <gtest/gtest.h>
 
@@ -77,4 +78,22 @@
     EXPECT_EQ(NO_MEMORY, String8("").setTo(in, SIZE_MAX));
 }
 
+// http://b/29250543
+TEST_F(String8Test, CorrectInvalidSurrogate) {
+    // d841d8 is an invalid start for a surrogate pair. Make sure this is handled by ignoring the
+    // first character in the pair and handling the rest correctly.
+    String16 string16(u"\xd841\xd841\xdc41\x0000");
+    String8 string8(string16);
+
+    EXPECT_EQ(4U, string8.length());
+}
+
+TEST_F(String8Test, CheckUtf32Conversion) {
+    // Since bound checks were added, check the conversion can be done without fatal errors.
+    // The utf8 lengths of these are chars are 1 + 2 + 3 + 4 = 10.
+    const char32_t string32[] = U"\x0000007f\x000007ff\x0000911\x0010fffe";
+    String8 string8(string32);
+    EXPECT_EQ(10U, string8.length());
+}
+
 }