finally understood why the use-after-free bug happened

TODO.md

@@ -6,6 +6,7 @@ Files:-
 Playback issues in the example program that may relate to the decoder:-
 23 - Crunchy loud noise mixed with the actual audio data
 
+uncommon/02 -> 6 channel audio might be incorrect (not a decoder issue afaik)
 uncommon/04 -> We get a bits per sample mismatch
 uncommon/10 -> We error with Invalid Signature. I assume for these two I should look for the frame sync bits. But maybe my decoder should reject these. idk.
 uncommon/11 -> We error with Invalid Signature
@@ -34,8 +35,10 @@ Things:-
 [ ] Speed optimizations
 [ ] Seeking
 [ ] Fuzzing to test the stability of the code
-[ ] Check if the use-after-free bug happens on Windows, and if so, if the address sanitizer will show us the full stacktrace
+[x] Check if the use-after-free bug happens on Windows, and if so, if the address sanitizer will show us the full stacktrace
 	instead of skipping some procs.
+	This was caused by `read_data()` and the tee reader writing into the buffer and us using some memory that was freed while the buffer
+	resized. Solution is to use buffer data BEFORE calling `read_data()`
 
 [ ] Encoder (low priority for now)
 

example/main_linux.odin

@@ -1,4 +1,4 @@
-package flac_example
+package flac_linux_example
 
 import "core:fmt"
 import "core:mem"
@@ -51,13 +51,13 @@ main :: proc() {
         os.exit(1)
     }
 
-    sample_rate := flac_data.metadata.sample_rate
+	// TODO: channel mapping is incorrect for anything with more than 2 channels.
     channels := flac_data.metadata.channels
 
     md5_ctx: md5.Context
     md5.init(&md5_ctx)
     for {
-        frame, err := flac.read_next_frame(reader, flac_data)
+        frame, err := flac.read_next_frame(reader, flac_data, allocator)
         if err != nil {
             if err == .EOF {
                 break
@@ -67,20 +67,24 @@ main :: proc() {
             }
         }
 
-        //if frame.sample_rate != sample_rate || frame.channels != channels {
+        if frame.channels != channels {
-        //  sample_rate = frame.sample_rate
+			// Finish playing the previous frame before changing the hw params.
-        //  channels = frame.channels
+			alsa.pcm_drain(handle)
-        //  alsa_err = alsa.pcm_set_params(handle, .S16_LE, .RW_INTERLEAVED, u32(channels), sample_rate, 1, 0)
+
-        //  if alsa_err < 0 {
+			channels = frame.channels
-        //      fmt.eprintln("Playback open error:", alsa.strerror(alsa_err))
+			alsa_err = alsa.pcm_set_params(handle, .S16_LE, .RW_INTERLEAVED, u32(channels), flac_data.metadata.sample_rate, 1, 500000)
-        //      os.exit(1)
+			if alsa_err < 0 {
-        //  }
+				fmt.eprintln("Playback open error:", alsa.strerror(alsa_err))
-        //}
+				os.exit(1)
+			}
+        }
+
+		// TODO: resampling
 
 		// 8 bps audio
-        //converted_samples := make([]u8, len(samples))
+        //converted_samples := make([]u8, len(frame.samples))
         //defer delete(converted_samples)
-        //for sample, i in samples {
+        //for sample, i in frame.samples {
         //    converted_samples[i] = u8(sample & 0xFF)
         //}
 
@@ -102,13 +106,6 @@ main :: proc() {
 
         flac.md5hash(&md5_ctx, flac_data.metadata.bits_per_sample, frame.samples)
     }
-    end := time.now()
-
-    err = flac.md5sum(&md5_ctx, flac_data)
-    if err == .MD5_Mismatch {
-        fmt.println("Decoded audio data is not correct.")
-        os.exit(1)
-    }
 
     alsa_err = alsa.pcm_drain(handle)
     if alsa_err < 0 {
@@ -116,6 +113,14 @@ main :: proc() {
     }
     alsa.pcm_close(handle)
 
+    end := time.now()
+
+    err = flac.md5sum(&md5_ctx, flac_data)
+    if err == .MD5_Mismatch {
+        fmt.printfln("Decoded audio data is not correct. Expected MD5: %v, Got: %v", flac_data.metadata.expected_md5, flac_data.metadata.calculated_md5)
+        os.exit(1)
+    }
+
     elapsed := time.diff(start, end)
     fmt.println("Decoding took", elapsed)
 }

flac.odin

@@ -591,10 +591,6 @@ read_next_frame :: proc(r: ^Reader, flac: ^Flac, allocator := context.allocator)
     tee_r: io.Tee_Reader
 
     crc_buffer: Buffer
-    // NOTE: using the default heap allocator here causes a use-after-free bug on files subset/05, subset/06, and subset/25
-    // No idea what the cause of the bug is.
-    //
-    // Resolved without understanding the root issue. See below code for a note on this.
     buffer_init_allocator(&crc_buffer, 0, 128)
     defer buffer_destroy(&crc_buffer)
 
@@ -806,13 +802,6 @@ read_next_frame :: proc(r: ^Reader, flac: ^Flac, allocator := context.allocator)
     // Frame Footer
     //
     crc16_bytes := buffer_to_bytes(&crc_buffer)
-    // NOTE: The order of these two calls is important. If we're using the default heap allocator
-    // for crc_buffer and we call read_data before calculate_crc16 then we run into a memory bug.
-    // I'm still not sure the root cause of the bug but it disappears when they're in this order.
-    //
-    // In the below cases the bug doesn't happen and the order doesn't matter.
-    // When using the temp allocator or an arena allocator.
-    // When using the reader from the arguments instead of the tee reader.
     calculated_frame_crc := calculate_crc16(crc16_bytes)
     frame_crc := u16(read_data(r, u16be) or_return)
 

internal.odin

@@ -6,6 +6,7 @@ import "core:crypto/legacy/md5"
 FLAC_MAGIC :: 'f' << 24 | 'L' << 16 | 'a' << 8 | 'C'
 
 //odinfmt: disable
+@(rodata)
 crc8_lookup := [256]u8 {
     0x00, 0x07, 0x0E, 0x09, 0x1C, 0x1B, 0x12, 0x15,
     0x38, 0x3F, 0x36, 0x31, 0x24, 0x23, 0x2A, 0x2D,
@@ -41,6 +42,7 @@ crc8_lookup := [256]u8 {
     0xE6, 0xE1, 0xE8, 0xEF, 0xFA, 0xFD, 0xF4, 0xF3,
 }
 
+@(rodata)
 crc16_lookup := [256]u16 {
     0x0000, 0x8005, 0x800F, 0x000A, 0x801B, 0x001E, 0x0014, 0x8011,
     0x8033, 0x0036, 0x003C, 0x8039, 0x0028, 0x802D, 0x8027, 0x0022,