From 4d41bd3ad9e978b16cc2f548ee3ed88e406adc2f Mon Sep 17 00:00:00 2001
From: crux161 <eain161@gmail.com>
Date: Fri, 29 May 2026 16:39:55 -0700
Subject: [PATCH] mount: probe VBR for GPT entries with unrecognized type GUIDs

Only Microsoft Basic Data and Linux Filesystem Data GPT partition
entries are currently inspected, so standard filesystems placed behind
other type GUIDs are skipped. For example, 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) for any entry
whose type GUID is non-empty and was not handled by the dedicated
branches.

A GPT entry's LBA span is also validated against the logical unit's
block_count at the top of the function, before any branch issues a
read. This guards every branch against uninitialized/garbage partition
array entries (e.g. a type GUID 0xF4-filled with lba_start ==
0xF4F4F4F4F4F4F4F4) whose reads would target out-of-range LBAs and can
stall flaky USB drives, force a BOT mass-storage reset and drop them
off the bus.
---
 source/usbhsfs_mount.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/source/usbhsfs_mount.c b/source/usbhsfs_mount.c
index df5cb7f..68da635 100644
--- a/source/usbhsfs_mount.c
+++ b/source/usbhsfs_mount.c
@@ -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;
 
@@ -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 an */
+    /* lba_start of 0xF4F4F4F4F4F4F4F4), whose reads would target absurd LBAs that 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)
+    {
+        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. */
@@ -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)))
+    {
+        /* This entry carries a non-empty type GUID that none of the branches above recognised; entries with an */
+        /* all-zero (empty) type GUID are unused and skipped here. Some tools place standard exFAT/FAT/NTFS (or */
+        /* even EXT) volumes behind such GUIDs -- e.g. 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. */
+        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);
+#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
     }