admin/ci-libretro-fceumm
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

core: memory-safety, leak, and savestate-portability audit fixes

Browse Source 
Squashed series of ~50 distinct bugs found during a multi-day
security/correctness audit, ranging from ROM-triggerable heap
corruption and savestate-triggered OOB read primitives down to
obscure cross-platform savestate breakage.

Build is clean on `make platform=unix` with zero new warnings.

CRITICAL (ROM-triggerable, exploitable on the user's machine)
=============================================================

* ines.c iNES 2.0 PRG/CHR exponent overflow leading to undersized
  allocation followed by heap buffer overflow on fread (pow() with
  attacker-chosen exponent up to 63). Cap exponent at 30 and
  compute size in uint32 with explicit cap below 2 GiB before
  storing in int.
* ines.c miscROMSize int wraparound from attacker-controlled PRG/
  CHR sizes; previous '& 0x8000000' check missed common underflow
  cases. Compute in int64 and reject <= 0 or > 128 MiB.
* unif.c MAPR chunk OOB heap read on chunks of size < 4. Validate
  chunk size before allocating board-name buffer.
* unif.c chunk size truncation: int conversion + missing cap allowed
  a 4 GiB chunk size to wrap. Cap at 16 MiB.
* unif.c FixRomSize infinite loop on size > 0x80000000. Cap input.
* unif.c DINF chunk: months[(m - 1) % 12] is UB for m==0; m comes
  from the .unf file. Clamp m into [1..12] before subtracting.
* unif.c NAME chunk: GameInfo->name = malloc(...) was unchecked.
* nsf.c size underflow: FCEU_fgetsize() - 0x80 wraps to ~UINT64_MAX
  on tiny files, propagating a huge size into uppow2/FCEU_malloc.
  Validate size > 0x80 before subtracting.
* nsf.c NSFMaxBank * 4096 cap tightened from 1<<20 (UB on signed-int
  overflow) to 1<<19 (fits in int).
* general.c uppow2 had signed-int UB (1 << 32) and wrapped to 0 for
  inputs near uint32 max. Cap at 0x80000000.
* cheat.c SubCheats[256] BSS overflow when more than 256 GG/PAR
  substitution cheats are active. The array is adjacent to MMapPtrs[64]
  in BSS which is exposed via retro_get_memory_data, making this
  overflow visible from outside the core.
* libretro.c retro_cheat_set strcpy stack overflow with arbitrary-
  length cheat strings from the frontend. Use strlcpy.

CRITICAL (savestate-triggerable on a malicious .fcs file)
=========================================================

* fds.c FDS savestate OOB read primitive: InDisk loaded from
  savestate is used as index into 8-element diskdata[] static
  pointer array. A value 8..254 dereferences arbitrary memory as
  a pointer (heap-read primitive). Also bounds-checked SelectDisk,
  mapperFDS_block, mapperFDS_blockstart, mapperFDS_diskaddr,
  mapperFDS_blocklen so blockstart+diskaddr stays within the 65500-
  byte disk buffer.
* 11 mappers had savestate-loaded variables masked at write time
  but not at restore time, used as indices into fixed arrays:
    - 88.c, KS7037.c, 112.c   cmd indexes reg[8]
    - sachen.c (S8259, S74LS374N) cmd indexes latch[8]
    - 357.c    dipswitch indexes outer_bank[4]
    - unrom512.c flash_state indexes erase_a/d/b[5]
    - 368.c    preg indexes banks[8]
    - 69.c     sndcmd indexes sreg[14]
    - mmc2and4.c latch0/latch1 index creg[4]
  None individually exploitable into RCE - the array writes corrupt
  adjacent BSS with constrained data flowing in - but each is an
  out-of-bounds read or write from attacker-controllable input.

HIGH (memory-safety, reachable on any load)
===========================================

* fceu-memory.c FCEU_malloc deref-of-NULL on allocation failure
  ('ret = 0; memset(ret, 0, size);').
* file.c multiple FCEUFILE/MakeMemWrap/MakeMemWrapBuffer unchecked
  allocations and unchecked filestream_tell return.
* libretro.c GameInfo NULL-derefs in three entry points
  (retro_set_controller_port_device, retro_get_memory_data,
  retro_get_memory_size) reachable on operations called before a
  successful load.
* libretro.c framebuffer leak ~256 KB per failed FCEUI_LoadGame
  (the libretro frontend doesn't call retro_unload_game on a
  failed load).
* libretro.c 3DS retro_deinit unchecked linearFree.
* libretro.c stereo / NTSC filter unchecked malloc returns.
* fceu.c FCEUI_LoadGame unchecked GameInfo malloc.
* fds.c SubLoad and FDSLoad unchecked FCEU_malloc on diskdatao
  backup buffers (NULL-deref in subsequent memcpy).
* fceu.c AllocGenieRW partial-failure leak: AReadG allocated but
  BWriteG malloc fails -> 256 KB leak per retry.
* input/bworld.c Update(): unbounded strcpy from attacker-supplied
  data into 20-byte bdata. Replaced with length-bounded copy.
* cart.c setprg2r/4r and setchr1r/2r/4r/8r mask-underflow guards.
  SetupCartPRGMapping/SetupCartCHRMapping compute (size >> N) - 1
  which underflows to 0xFFFFFFFF for chips smaller than the unit.
  setprg8r/16r/32r and setchr8r already had defensive size checks;
  the smaller units did not. malee.c (2 KB chip) and mapper 218
  (2 KB NTARAM-as-CHR) accidentally avoid OOB; the primitive is
  unsafe for any future board.
* video.c FCEU_InitVirtualVideo XBuf/XDBuf partial-failure leak.
* video.c, fceu.c FCEU_DispMessage / FCEU_printf / FCEU_PrintError:
  vsprintf into fixed stack buffers replaced with vsnprintf.
* core: validate magic-string read length on FDS/UNIF/NSF load
  (reject files too short to contain the magic so previous static
  buffer / stack garbage doesn't spuriously match).

LEAKS (every cart load/unload cycle)
====================================

* mmc5.c MMC5 cart-side: WRAM (up to 64K) + MMC5fill (1K) + ExRAM
  (1K) leaked per cycle. NSFMMC5_Close existed but was only used
  for NSF code path.
* onebus.c Mapper 270/436: 8 KB CHRRAM leaked per cycle.
* 330.c, 375.c, 528.c: 8 KB WRAM each, no Close at all.

CORRECTNESS (UB / ABI / endianness)
===================================

* fceu-endian.c FlipByteOrder loop bound was 'count' instead of
  'count/2', making it a no-op for every even count and silently
  breaking savestate portability for every FCEUSTATE_RLSB-marked
  field. The '#ifndef GEKKO' workarounds scattered through the
  codebase (sound.c, vrc7.c, vrc6.c) were symptoms of this root
  cause.
* state.c AddExState bounds check ran AFTER writing the entry, so
  when SFEXINDEX hit the 63-entry cap the next call would write
  the entry then immediately overwrite it with the terminator.
* state.c FCEUSS_Save_Mem: post-save callback was guarded by
  'if (SPreSave)' instead of 'if (SPostSave)'.
* Sequence-point UB in counter expressions across 4 board files,
  e.g. 'x = !x ? a : --x' and 'x = ++x % n'. GCC -Wsequence-point
  flags all five sites (285.c, 413.c, asic_mmc3.c, jyasic.c).
* SFORMAT size mismatches between declared variable type and
  AddExState size argument:
    - asic_vrc3.c VRC3_count/VRC3_reload (uint16, saved as 1 byte)
    - mmc3.c m555_count (uint32, saved as 2 bytes), m555_count_-
      expired (uint8, saved as 2 bytes - OOB write into adjacent
      BSS).
* unrom512.c UNROM-512 mapper 30 .srm save format: host-endian
  uint32 flash write counters. Now stored as LE on disk regardless
  of host (Battle Kid 2, Twin Dragons, Lizard, Sole, etc.).
* ~70 multi-byte single-variable SFORMAT/AddExState entries across
  36 board files were saved as host-byte-order. After the
  FlipByteOrder fix, these are now byte-swapped on BE so cross-
  platform savestates round-trip correctly.
* coolgirl.c new ExStateLE() macro added; 22 multi-byte sites.
* pic16c5x.c 11 multi-byte AddExState calls (m_PC, m_PREVPC,
  m_CONFIG, m_WDT, m_prescaler, m_opcode, m_STACK[0/1], m_icount,
  m_delay_timer, m_rtcc, m_inst_cycles, m_clock2cycle).
* onebus.c PowerJoy Supermax submapper detection used non-portable
  *(uint32*)&info->MD5 cast that read different bytes on LE vs BE.
* fds.c clean up redundant FCEUSTATE_RLSB encoding in AddExState
  calls that also passed type=1 (idempotent OR; readability fix).

DOCUMENTATION
=============

* input.c UpdateGP's *(uint32*)data cast looks like a typical
  endian bug but is actually correct (the libretro frontend builds
  JSReturn with matching host-uint32 shifts). Comment added to
  prevent future "fixes" from breaking it.

Limitations not addressed
=========================

* Element-stride-aware byte swapping. The savestate byte-swap
  mechanism (FlipByteOrder over the entire SFORMAT entry buffer)
  is structurally wrong for arrays of multi-byte values: it
  reverses the whole buffer end-to-end instead of byte-swapping
  each element. Several places that need cross-platform-portable
  arrays (VRC7 sound state, jyasic chr[8]) work around this by
  either splitting arrays into per-element SFORMAT entries (n106
  PlayIndex, bandai reg) or by skipping save entirely on BE via
  #ifndef GEKKO. A proper fix would extend the size encoding with
  an element-stride field. Left for a future change because it
  would change the savestate format.

* Strict-aliasing UB in ppu.c (around 9 sites doing
  *(uint32*)uint8_buf for fast 4-byte writes via FCEU_dwmemset).
  Works in practice with all common compilers because the patterns
  are byte-symmetric, but is formally UB.

* FCEU_gmalloc calls exit(1) on OOM. A libretro core should never
  exit() because that takes down the whole frontend. Used by
  100+ call sites; refactoring to return-NULL is out of scope here.

Testing
=======

* Build: clean on `make platform=unix` with -O2; no new warnings.
* FlipByteOrder fix verified by hand-trace and a standalone unit
  test for counts 2, 4, 8.
* uppow2 fix verified by unit test across 13 boundary cases.
* SFORMAT size mismatches and missing-RLSB cases identified by
  Python static-analysis scripts that cross-reference SFORMAT
  entries against variable declarations.
* iNES 2.0 exponent fix verified by hand-tracing what byte 0xFF
  produces post-fix: exp=30 (capped), mult=7, size=3 GiB nominal,
  capped to 1 GiB, capped to 2 GiB by uppow2, FCEU_malloc returns
  NULL on most systems, loader returns 0. No heap overflow for
  any input byte.
* Savestate-loaded array index audit: built a Python scanner that
  extracts each AddExState/SFORMAT entry and cross-references the
  variable name against array-index uses in the same file. All
  flagged sites covered.
* A libFuzzer harness and seed corpus generator (fuzz_main.c,
  gen_seed_corpus.py) accompany this submission for ongoing
  regression testing.
This commit is contained in:
U-DESKTOP-SPFP6AQ\twistedtechre
2026-05-04 02:15:40 +02:00
parent 448a231618
commit 1185db89c1
73 changed files with 595 additions and 165 deletions
Download Patch File Download Diff File Expand all files Collapse all files

49
src/drivers/libretro/libretro.c
View File

@@ -1050,6 +1050,13 @@ static void stereo_filter_apply_delay(int32_t *sound_buffer, size_t size)
tmp_buffer_size = (tmp_buffer_size << 1) - (tmp_buffer_size >> 1);
tmp_buffer = (int32_t *)malloc(tmp_buffer_size * sizeof(int32_t));
if (!tmp_buffer)
{
/* On allocation failure, drop this batch rather than dereferencing
* a NULL buffer in the memcpy below. The next batch will retry. */
return;
}
memcpy(tmp_buffer, stereo_filter_delay.samples,
stereo_filter_delay.samples_pos * sizeof(int32_t));
@@ -1137,6 +1144,15 @@ static void stereo_filter_init_delay(void)
stereo_filter_delay.samples = (int32_t *)malloc(
initial_samples_size * sizeof(int32_t));
if (!stereo_filter_delay.samples)
{
/* Fall back to the null filter on allocation failure rather than
* leaving a NULL samples buffer that the apply path would deref. */
stereo_filter_delay.samples_size = 0;
stereo_filter_delay.samples_pos = 0;
stereo_filter_apply = stereo_filter_apply_null;
return;
}
stereo_filter_delay.samples_size = initial_samples_size;
stereo_filter_delay.samples_pos = 0;
@@ -1433,7 +1449,7 @@ void retro_set_controller_port_device(unsigned port, unsigned device)
{
if (device != RETRO_DEVICE_AUTO)
update_nes_controllers(port, device);
else
else if (GameInfo) /* GameInfo may be NULL pre-load */
update_nes_controllers(port, nes_to_libretro(GameInfo->input[port]));
}
else
@@ -1460,7 +1476,7 @@ void retro_set_controller_port_device(unsigned port, unsigned device)
{
if (device != RETRO_DEVICE_FC_AUTO)
update_nes_controllers(4, device);
else
else if (GameInfo) /* GameInfo may be NULL pre-load */
update_nes_controllers(4, fc_to_libretro(GameInfo->inputfc));
}
@@ -1921,7 +1937,9 @@ void retro_deinit (void)
FCEUI_Sound(0);
FCEUI_Kill();
#if defined(_3DS)
linearFree(fceu_video_out);
if (fceu_video_out)
linearFree(fceu_video_out);
fceu_video_out = NULL;
#else
if (fceu_video_out)
free(fceu_video_out);
@@ -3057,6 +3075,8 @@ size_t retro_serialize_size(void)
{
/* Something arbitrarily big.*/
uint8_t *buffer = (uint8_t*)malloc(1000000);
if (!buffer)
return 0;
memstream_set_buffer(buffer, 1000000);
FCEUSS_Save_Mem();
@@ -3130,7 +3150,7 @@ void retro_cheat_reset(void)
void retro_cheat_set(unsigned index, bool enabled, const char *code)
{
char name[256];
char temp[256];
char temp[1024];
char *codepart;
uint16 a;
uint8 v;
@@ -3140,8 +3160,12 @@ void retro_cheat_set(unsigned index, bool enabled, const char *code)
if (code == NULL)
return;
/* Cheat strings can be arbitrarily long (multiple codes joined by
* separators). The previous strcpy into a 256-byte stack buffer was
* trivially overflowable. Use strlcpy and a larger buffer; truncate
* if necessary rather than overflow. */
sprintf(name, "N/A");
strcpy(temp, code);
strlcpy(temp, code, sizeof(temp));
codepart = strtok(temp, "+,;._ ");
while (codepart)
@@ -3685,6 +3709,17 @@ bool retro_load_game(const struct retro_game_info *info)
if (!GameInfo)
{
/* On load failure the libretro frontend won't call retro_unload_game,
* so free the framebuffer we just allocated to avoid leaking ~256 KB
* per failed load. */
#if defined(_3DS)
if (fceu_video_out)
linearFree(fceu_video_out);
#elif !defined(PSP)
if (fceu_video_out)
free(fceu_video_out);
#endif
fceu_video_out = NULL;
#if 0
/* An error message here is superfluous - the frontend
* will report that content loading has failed */
@@ -3858,7 +3893,7 @@ void *retro_get_memory_data(unsigned type)
return iNESCart.SaveGame[0];
else if (UNIFCart.battery && UNIFCart.SaveGame[0] && UNIFCart.SaveGameLen[0])
return UNIFCart.SaveGame[0];
else if (GameInfo->type == GIT_FDS)
else if (GameInfo && GameInfo->type == GIT_FDS)
return FDSROM_ptr();
else
data = NULL;
@@ -3885,7 +3920,7 @@ size_t retro_get_memory_size(unsigned type)
size = iNESCart.SaveGameLen[0];
else if (UNIFCart.battery && UNIFCart.SaveGame[0] && UNIFCart.SaveGameLen[0])
size = UNIFCart.SaveGameLen[0];
else if (GameInfo->type == GIT_FDS)
else if (GameInfo && GameInfo->type == GIT_FDS)
size = FDSROM_size();
else
size = 0;