Fix fread returning bad data.
Bug: 19172514
Change-Id: I05016577858a02aca7d14e75e6ec28abc925037c
diff --git a/libc/stdio/fread.c b/libc/stdio/fread.c
index bac8dad..f3f0127 100644
--- a/libc/stdio/fread.c
+++ b/libc/stdio/fread.c
@@ -102,6 +102,12 @@
* avoid copying it through the buffer?
*/
if (total > (size_t) fp->_bf._size) {
+ /*
+ * Make sure that fseek doesn't think it can
+ * reuse the buffer since we are going to read
+ * directly from the file descriptor.
+ */
+ fp->_flags |= __SMOD;
break;
}
diff --git a/tests/stdio_test.cpp b/tests/stdio_test.cpp
index 890e86e..2ecfc60 100644
--- a/tests/stdio_test.cpp
+++ b/tests/stdio_test.cpp
@@ -965,3 +965,41 @@
TEST(stdio, fwrite_after_fread_fast_path) {
test_fwrite_after_fread(64*1024);
}
+
+// http://b/19172514
+TEST(stdio, fread_after_fseek) {
+ TemporaryFile tf;
+
+ FILE* fp = fopen(tf.filename, "w+");
+ ASSERT_TRUE(fp != nullptr);
+
+ char file_data[12288];
+ for (size_t i = 0; i < 12288; i++) {
+ file_data[i] = i;
+ }
+ ASSERT_EQ(12288U, fwrite(file_data, 1, 12288, fp));
+ fclose(fp);
+
+ fp = fopen(tf.filename, "r");
+ ASSERT_TRUE(fp != nullptr);
+
+ char buffer[8192];
+ size_t cur_location = 0;
+ // Small read to populate internal buffer.
+ ASSERT_EQ(100U, fread(buffer, 1, 100, fp));
+ ASSERT_EQ(memcmp(file_data, buffer, 100), 0);
+
+ cur_location = static_cast<size_t>(ftell(fp));
+ // Large read to force reading into the user supplied buffer and bypassing
+ // the internal buffer.
+ ASSERT_EQ(8192U, fread(buffer, 1, 8192, fp));
+ ASSERT_EQ(memcmp(file_data+cur_location, buffer, 8192), 0);
+
+ // Small backwards seek to verify fseek does not reuse the internal buffer.
+ ASSERT_EQ(0, fseek(fp, -22, SEEK_CUR));
+ cur_location = static_cast<size_t>(ftell(fp));
+ ASSERT_EQ(22U, fread(buffer, 1, 22, fp));
+ ASSERT_EQ(memcmp(file_data+cur_location, buffer, 22), 0);
+
+ fclose(fp);
+}