Improve the extent tree node validation by validating the number of
entries the node advertises against the theoretical max (derived from
the size of on-disk structs and the block size (or i_data, if inline
extents).
Previously, we did not validate the number of entries. This could be
exploited for out-of-bounds reads and crashes.
Cc: Marvin Häuser <mhaeu...@posteo.de>
Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
Reported-by: Savva Mitrofanov <savva...@gmail.com>
Signed-off-by: Pedro Falcato <pedro.falc...@gmail.com>
---
Features/Ext4Pkg/Ext4Dxe/Extents.c | 32 ++++++++++++++++++++++++++----
1 file changed, 28 insertions(+), 4 deletions(-)
diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c
b/Features/Ext4Pkg/Ext4Dxe/Extents.c
index 9e4364e50d99..2b82417c9e10 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Extents.c
+++ b/Features/Ext4Pkg/Ext4Dxe/Extents.c
@@ -1,7 +1,7 @@
/** @file
Extent related routines
- Copyright (c) 2021 - 2022 Pedro Falcato All rights reserved.
+ Copyright (c) 2021 - 2023 Pedro Falcato All rights reserved.
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
@@ -80,13 +80,15 @@ Ext4GetInoExtentHeader (
/**
Checks if an extent header is valid.
@param[in] Header Pointer to the EXT4_EXTENT_HEADER structure.
+ @param[in] MaxEntries Maximum number of entries possible for this
tree node.
@return TRUE if valid, FALSE if not.
**/
STATIC
BOOLEAN
Ext4ExtentHeaderValid (
- IN CONST EXT4_EXTENT_HEADER *Header
+ IN CONST EXT4_EXTENT_HEADER *Header,
+ IN UINT16 MaxEntries
)
{
if (Header->eh_depth > EXT4_EXTENT_TREE_MAX_DEPTH) {
@@ -99,6 +101,18 @@ Ext4ExtentHeaderValid (
return FALSE;
}
+ // Note: We do not need to check eh_entries here, as the next branch makes
sure max >= entries
+ if (Header->eh_max > MaxEntries) {
+ DEBUG ((
+ DEBUG_ERROR,
+ "[ext4] Invalid extent header max entries (%u eh_max, "
+ "theoretical max is %u) (larger than permitted)\n",
+ Header->eh_max,
+ MaxEntries
+ ));
+ return FALSE;
+ }
+
if (Header->eh_max < Header->eh_entries) {
DEBUG ((
DEBUG_ERROR,
@@ -212,6 +226,9 @@ Ext4ExtentIdxLeafBlock (
return LShiftU64 (Index->ei_leaf_hi, 32) | Index->ei_leaf_lo;
}
+// Results of sizeof(i_data) / sizeof(extent) - 1 = 4
+#define EXT4_NR_INLINE_EXTENTS 4
+
/**
Retrieves an extent from an EXT4 inode.
@param[in] Partition Pointer to the opened EXT4 partition.
@@ -237,6 +254,7 @@ Ext4GetExtent (
EXT4_EXTENT_HEADER *ExtHeader;
EXT4_EXTENT_INDEX *Index;
EFI_STATUS Status;
+ UINT32 MaxExtentsPerNode;
EXT4_BLOCK_NR BlockNumber;
Inode = File->Inode;
@@ -275,12 +293,17 @@ Ext4GetExtent (
ExtHeader = Ext4GetInoExtentHeader (Inode);
- if (!Ext4ExtentHeaderValid (ExtHeader)) {
+ if (!Ext4ExtentHeaderValid (ExtHeader, EXT4_NR_INLINE_EXTENTS)) {
return EFI_VOLUME_CORRUPTED;
}
CurrentDepth = ExtHeader->eh_depth;
+ // A single node fits into a single block, so we can only have (BlockSize /
sizeof(EXT4_EXTENT)) - 1
+ // extents in a single node. Note the -1, because both leaf and internal
node headers are 12 bytes,
+ // and so are individual entries.
+ MaxExtentsPerNode = (Partition->BlockSize / sizeof (EXT4_EXTENT)) - 1;
+
while (ExtHeader->eh_depth != 0) {
CurrentDepth--;
// While depth != 0, we're traversing the tree itself and not any leaves
@@ -309,6 +332,7 @@ Ext4GetExtent (
}
// Read the leaf block onto the previously-allocated buffer.
+
Status = Ext4ReadBlocks (Partition, Buffer, 1, BlockNumber);
if (EFI_ERROR (Status)) {
FreePool (Buffer);
@@ -317,7 +341,7 @@ Ext4GetExtent (
ExtHeader = Buffer;
- if (!Ext4ExtentHeaderValid (ExtHeader)) {
+ if (!Ext4ExtentHeaderValid (ExtHeader, MaxExtentsPerNode)) {
FreePool (Buffer);
return EFI_VOLUME_CORRUPTED;
}
--
2.40.1
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