[PATCH v3 1/2] Ext4Pkg: Improve extent node validation on the number of entries

[PATCH v3 1/2] Ext4Pkg: Improve extent node validation on the number of entries

[Pedro Falcato]

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 <mhaeuser@posteo.de>
Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
Reported-by: Savva Mitrofanov <savvamtr@gmail.com>
Signed-off-by: Pedro Falcato <pedro.falcato@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

[PATCH v3 2/2] Ext4Pkg: Advertise CSUM_SEED as supported

[Pedro Falcato]

We had added support for CSUM_SEED but accidentally forgot to advertise
it in gSupportedIncompatFeat. This made it (erroneously) impossible to
mount CSUM_SEED filesystems.

Detected by attempting to mount a relatively new mkfs.ext4'd filesystem.

Cc: Marvin Häuser <mhaeuser@posteo.de>
Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Marvin Häuser <mhaeuser@posteo.de>
---
 Features/Ext4Pkg/Ext4Dxe/Superblock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Features/Ext4Pkg/Ext4Dxe/Superblock.c b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
index 3f56de93c105..604925b582c1 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Superblock.c
+++ b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
@@ -1,7 +1,7 @@
 /** @file
   Superblock managing 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
 **/
 
@@ -18,7 +18,7 @@ STATIC CONST UINT32  gSupportedIncompatFeat =
   EXT4_FEATURE_INCOMPAT_64BIT | EXT4_FEATURE_INCOMPAT_DIRDATA |
   EXT4_FEATURE_INCOMPAT_FLEX_BG | EXT4_FEATURE_INCOMPAT_FILETYPE |
   EXT4_FEATURE_INCOMPAT_EXTENTS | EXT4_FEATURE_INCOMPAT_LARGEDIR |
-  EXT4_FEATURE_INCOMPAT_MMP | EXT4_FEATURE_INCOMPAT_RECOVER;
+  EXT4_FEATURE_INCOMPAT_MMP | EXT4_FEATURE_INCOMPAT_RECOVER | EXT4_FEATURE_INCOMPAT_CSUM_SEED;
 
 // Future features that may be nice additions in the future:
 // 1) Btree support: Required for write support and would speed up lookups in large directories.
-- 
2.40.1

Re: [PATCH v3 1/2] Ext4Pkg: Improve extent node validation on the number of entries

[Marvin Häuser]

Reviewed-by: Marvin Häuser <mhaeuser@posteo.de>

> On 9. May 2023, at 17:49, Pedro Falcato <pedro.falcato@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 <mhaeuser@posteo.de>
> Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
> Reported-by: Savva Mitrofanov <savvamtr@gmail.com>
> Signed-off-by: Pedro Falcato <pedro.falcato@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
> 

Re: [PATCH v3 1/2] Ext4Pkg: Improve extent node validation on the number of entries

[Pedro Falcato]

Thank you! Merged the patchset as 82f4b39 and 9247980, respectively.

On Tue, May 9, 2023 at 5:07 PM Marvin Häuser <mhaeuser@posteo.de> wrote:
>
> Reviewed-by: Marvin Häuser <mhaeuser@posteo.de>
>
> > On 9. May 2023, at 17:49, Pedro Falcato <pedro.falcato@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 <mhaeuser@posteo.de>
> > Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
> > Reported-by: Savva Mitrofanov <savvamtr@gmail.com>
> > Signed-off-by: Pedro Falcato <pedro.falcato@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
> >
>


-- 
Pedro