Fix small ptrace reads.
The BacktracePtrace::Read function crashes if the number of bytes to
read is less than the number of bytes needed to align the read to
a word_t boundary.
Fix this and add a test for this case.
Change-Id: I50808849ece44928f65dba1d25309e3885c829a2
diff --git a/libbacktrace/BacktracePtrace.cpp b/libbacktrace/BacktracePtrace.cpp
index 6134438..e10cce1 100644
--- a/libbacktrace/BacktracePtrace.cpp
+++ b/libbacktrace/BacktracePtrace.cpp
@@ -83,13 +83,12 @@
if (!PtraceRead(Tid(), addr & ~(sizeof(word_t) - 1), &data_word)) {
return 0;
}
- align_bytes = sizeof(word_t) - align_bytes;
- memcpy(buffer, reinterpret_cast<uint8_t*>(&data_word) + sizeof(word_t) - align_bytes,
- align_bytes);
- addr += align_bytes;
- buffer += align_bytes;
- bytes -= align_bytes;
- bytes_read += align_bytes;
+ size_t copy_bytes = MIN(sizeof(word_t) - align_bytes, bytes);
+ memcpy(buffer, reinterpret_cast<uint8_t*>(&data_word) + align_bytes, copy_bytes);
+ addr += copy_bytes;
+ buffer += copy_bytes;
+ bytes -= copy_bytes;
+ bytes_read += copy_bytes;
}
size_t num_words = bytes / sizeof(word_t);
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index 28d146a..a086547 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -883,6 +883,17 @@
ASSERT_EQ(waitpid(pid, nullptr, 0), pid);
}
+void InitMemory(uint8_t* memory, size_t bytes) {
+ for (size_t i = 0; i < bytes; i++) {
+ memory[i] = i;
+ if (memory[i] == '\0') {
+ // Don't use '\0' in our data so we can verify that an overread doesn't
+ // occur by using a '\0' as the character after the read data.
+ memory[i] = 23;
+ }
+ }
+}
+
void* ThreadReadTest(void* data) {
thread_t* thread_data = reinterpret_cast<thread_t*>(data);
@@ -901,9 +912,7 @@
}
// Set up a simple pattern in memory.
- for (size_t i = 0; i < pagesize; i++) {
- memory[i] = i;
- }
+ InitMemory(memory, pagesize);
thread_data->data = memory;
@@ -931,9 +940,8 @@
// Create a page of data to use to do quick compares.
uint8_t* expected = new uint8_t[pagesize];
- for (size_t i = 0; i < pagesize; i++) {
- expected[i] = i;
- }
+ InitMemory(expected, pagesize);
+
uint8_t* data = new uint8_t[2*pagesize];
// Verify that we can only read one page worth of data.
size_t bytes_read = backtrace->Read(read_addr, data, 2 * pagesize);
@@ -947,6 +955,20 @@
ASSERT_TRUE(memcmp(data, &expected[i], 2 * sizeof(word_t)) == 0)
<< "Offset at " << i << " failed";
}
+
+ // Verify small unaligned reads.
+ for (size_t i = 1; i < sizeof(word_t); i++) {
+ for (size_t j = 1; j < sizeof(word_t); j++) {
+ // Set one byte past what we expect to read, to guarantee we don't overread.
+ data[j] = '\0';
+ bytes_read = backtrace->Read(read_addr + i, data, j);
+ ASSERT_EQ(j, bytes_read);
+ ASSERT_TRUE(memcmp(data, &expected[i], j) == 0)
+ << "Offset at " << i << " length " << j << " miscompared";
+ ASSERT_EQ('\0', data[j])
+ << "Offset at " << i << " length " << j << " wrote too much data";
+ }
+ }
delete data;
delete expected;
}
@@ -990,9 +1012,7 @@
}
// Set up a simple pattern in memory.
- for (size_t i = 0; i < pagesize; i++) {
- memory[i] = i;
- }
+ InitMemory(memory, pagesize);
g_addr = reinterpret_cast<uintptr_t>(memory);
g_ready = 1;