Reviewed-by: Marvin Häuser <mhaeu...@posteo.de>
> On 9. May 2023, at 17:49, Pedro Falcato <pedro.falc...@gmail.com> wrote:
>
> 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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