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mount: probe VBR for GPT entries with unrecognized type GUIDs #32

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mount: probe VBR for GPT entries with unrecognized type GUIDs #32

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28 changes: 28 additions & 0 deletions source/usbhsfs_mount.c
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Original file line number Diff line number Diff line change
Expand Up @@ -212,6 +212,7 @@ static Mutex g_devoptabDefaultDeviceMutex = 0;

static const u8 g_microsoftBasicDataPartitionGuid[0x10] = { 0xA2, 0xA0, 0xD0, 0xEB, 0xE5, 0xB9, 0x33, 0x44, 0x87, 0xC0, 0x68, 0xB6, 0xB7, 0x26, 0x99, 0xC7 }; /* EBD0A0A2-B9E5-4433-87C0-68B6B72699C7. */
static const u8 g_linuxFilesystemDataGuid[0x10] = { 0xAF, 0x3D, 0xC6, 0x0F, 0x83, 0x84, 0x72, 0x47, 0x8E, 0x79, 0x3D, 0x69, 0xD8, 0x47, 0x7D, 0xE4 }; /* 0FC63DAF-8483-4772-8E79-3D69D8477DE4. */
static const u8 g_emptyPartitionGuid[0x10] = {0};

static u32 g_fileSystemMountFlags = UsbHsFsMountFlags_Default;

Expand Down Expand Up @@ -714,6 +715,16 @@ static void usbHsFsMountParseGuidPartitionTableEntry(UsbHsFsDriveLogicalUnitCont
u64 entry_size = ((gpt_entry->lba_end + 1) - gpt_entry->lba_start);
UsbHsFsDriveLogicalUnitFileSystemType fs_type = UsbHsFsDriveLogicalUnitFileSystemType_Invalid;

/* Discard entries whose LBA span falls outside this logical unit before any branch below
* issues a read. This filters out uninitialized/garbage partition array entries (e.g. a
* type GUID 0xF4-filled with lba_start == 0xF4F4F4F4F4F4F4F4) whose reads would target
* absurd LBAs, which can stall flaky USB drives, force a BOT reset and knock them off the bus. */
if (entry_lba >= lun_ctx->block_count || gpt_entry->lba_end >= lun_ctx->block_count || gpt_entry->lba_end < entry_lba)
Comment on lines +718 to +722

@DarkMatterCore DarkMatterCore May 29, 2026

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Please make this comment block follow the same format as other multi-line comment blocks in this codebase by making each line sart with /* and end with */.

{
USBHSFS_LOG_MSG("Discarding GPT partition entry with out-of-range LBA span (0x%lX - 0x%lX) (interface %d, LUN %u).", entry_lba, gpt_entry->lba_end, lun_ctx->usb_if_id, lun_ctx->lun);
return;
}

if (!memcmp(gpt_entry->type_guid, g_microsoftBasicDataPartitionGuid, sizeof(g_microsoftBasicDataPartitionGuid)))
{
/* We're dealing with a Microsoft Basic Data Partition entry. */
Expand All @@ -738,6 +749,23 @@ static void usbHsFsMountParseGuidPartitionTableEntry(UsbHsFsDriveLogicalUnitCont
#ifdef GPL_BUILD
/* Check if this LBA points to a valid EXT superblock. Register the EXT volume if so. */
fs_type = usbHsFsMountInspectExtSuperBlock(lun_ctx, block, entry_lba);
#endif
} else
if (memcmp(gpt_entry->type_guid, g_emptyPartitionGuid, sizeof(g_emptyPartitionGuid)))
{
/* Some tools place standard exFAT/FAT/NTFS (or even EXT) volumes behind GPT type
* GUIDs other than the Microsoft Basic Data / Linux Filesystem Data ones handled
* above. For instance, the Windows Recovery Environment partition created by Windows
* Setup uses type GUID DE94BBA4-06D1-4D40-A16A-BFD50179D6AC, yet holds an NTFS volume.
* Probe the VBR (and, on GPL builds, the EXT superblock) before skipping the entry. */
Comment on lines +756 to +760

@DarkMatterCore DarkMatterCore May 29, 2026

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Please make this comment block follow the same format as other multi-line comment blocks in this codebase by making each line sart with /* and end with */.

@DarkMatterCore DarkMatterCore May 29, 2026

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On a second thought, the comment itself is misleading, since it doesn't really reference the fact that we're intentionally looking for an empty GUID here.

USBHSFS_LOG_MSG("Found unrecognized GPT partition type at LBA 0x%lX. Probing VBR (interface %d, LUN %u).", entry_lba, lun_ctx->usb_if_id, lun_ctx->lun);
fs_type = usbHsFsMountInspectVolumeBootRecord(lun_ctx, block, entry_lba);
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#ifdef GPL_BUILD
if (fs_type == UsbHsFsDriveLogicalUnitFileSystemType_Invalid)
{
/* The entry may instead point to an EXT volume sitting behind a non-standard GUID. */
fs_type = usbHsFsMountInspectExtSuperBlock(lun_ctx, block, entry_lba);
}
#endif
}

Expand Down