Undefined behavior in wuffs-v0.4.c

[tksuoran]

This could be somehow my own bad, as I've just started testing wuffs, but I decided to report this anyway:
When I run my code with ubsan, I get this kind of reports:

wuffs-v0.4.c:17220:14: runtime error: call to function wuffs_png__decoder__decode_image_config through pointer to incorrect function type 'wuffs_base__status__struct (*)(void *, wuffs_base__image_config__struct *, wuffs_base__io_buffer__struct *)'
wuffs-v0.4.c:61835: note: wuffs_png__decoder__decode_image_config defined here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior wuffs-v0.4.c:17220:14
wuffs-v0.4.c:17188:14: runtime error: call to function wuffs_png__decoder__decode_frame_config through pointer to incorrect function type 'wuffs_base__status__struct (*)(void *, wuffs_base__frame_config__struct *, wuffs_base__io_buffer__struct *)'
wuffs-v0.4.c:64123: note: wuffs_png__decoder__decode_frame_config defined here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior wuffs-v0.4.c:17188:14
wuffs-v0.4.c:17515:14: runtime error: call to function wuffs_png__decoder__workbuf_len through pointer to incorrect function type 'wuffs_base__range_ii_u64__struct (*)(const void *)'
wuffs-v0.4.c:65979: note: wuffs_png__decoder__workbuf_len defined here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior wuffs-v0.4.c:17515:14
wuffs-v0.4.c:17156:14: runtime error: call to function wuffs_png__decoder__decode_frame through pointer to incorrect function type 'wuffs_base__status__struct (*)(void *, wuffs_base__pixel_buffer__struct *, wuffs_base__io_buffer__struct *, unsigned char, wuffs_base__slice_u8, wuffs_base__decode_frame_options__struct *)'
wuffs-v0.4.c:64611: note: wuffs_png__decoder__decode_frame defined here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior wuffs-v0.4.c:17156:14

[tksuoran]

I can work around the issue by this:

#pragma clang attribute push (__attribute__((no_sanitize("undefined"))), apply_to=function)
#include "wuffs-v0.4.c"
#pragma clang attribute pop

but I think this is less than ideal.

[nigeltao]

Can you share the ubsan-using command line that triggers this?

[tksuoran]

While investigating another issue - gabime/spdlog#3145 - I run Microsoft Visual C++ Redistributable repair, and after that, I can no longer reproduce this undefined behavior. This suggests the issue was in somehow caused by old or broken Microsoft Visual C++ Redistributable.

I wish Microsoft would have added some sort of version check when they did breaking change (microsoft/STL#4730).

[nigeltao]

OK, not reproducible.

Still, you mentioned "Microsoft Visual C++ Redistributable" but also #pragma clang. Out of curiosity: were you compiling with MSVC or with clang?

[nigeltao]

And, in case this gets re-opened later, I am unable to reproduce any ubsan warnings. With this patch:

$ git diff
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 1a197f73..9b7019d0 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -1,6 +1,9 @@
 #ifndef WUFFS_INCLUDE_GUARD
 #define WUFFS_INCLUDE_GUARD
 
+#include <stdio.h>
+int trigger_ubsan = 0x7fffffff;
+
 // Wuffs ships as a "single file C library" or "header file library" as per
 // https://github.com/nothings/stb/blob/master/docs/stb_howto.txt
 //
@@ -17181,6 +17184,7 @@ wuffs_base__image_decoder__decode_frame_config(
     wuffs_base__image_decoder* self,
     wuffs_base__frame_config* a_dst,
     wuffs_base__io_buffer* a_src) {
+fprintf(stderr, "wuffs_base__image_decoder__decode_frame_config\n");
   if (!self) {
     return wuffs_base__make_status(wuffs_base__error__bad_receiver);
   }
@@ -64136,6 +64140,8 @@ wuffs_png__decoder__decode_frame_config(
     wuffs_png__decoder* self,
     wuffs_base__frame_config* a_dst,
     wuffs_base__io_buffer* a_src) {
+fprintf(stderr, "wuffs_png__decoder__decode_frame_config\n");
+if (trigger_ubsan++ == 123456) { fprintf(stderr, "undefined behavior! (int overflow)\n"); }
   if (!self) {
     return wuffs_base__make_status(wuffs_base__error__bad_receiver);
   }

I get this output:

$ clang-14 -fsanitize=undefined test/c/std/png.c && ./a.out
wuffs_base__image_decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
test/c/std/../../../release/c/wuffs-unsupported-snapshot.c:64144:18: runtime error: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior test/c/std/../../../release/c/wuffs-unsupported-snapshot.c:64144:18 in 
wuffs_base__image_decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_base__image_decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
wuffs_png__decoder__decode_frame_config
std/png         clang14 PASS (12 tests)

So, ubsan is triggering, but if I take out the trigger_ubsan++ == 123456 line, ubsan is no longer triggered. I don't get the test/c/std/... runtime error: signed integer overflow... SUMMARY: UndefinedBehaviorSanitizer... lines.

[tksuoran]

OK, not reproducible.

Still, you mentioned "Microsoft Visual C++ Redistributable" but also #pragma clang. Out of curiosity: were you compiling with MSVC or with clang?

I was compiling in msys2 clang64 environment using clang:

$ clang++ --version
clang version 18.1.8
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:/msys64/clang64/bin

AFAIK, msvc does not support ubsan currently.