[edk2-devel] [edk2-platforms][PATCH v3 05/11] Ext4Pkg: Fix shift out of bounds in Ext4OpenSuperblock

[Savva Mitrofanov]

Missing check for wrong s_log_block_size exponent leads to shift out of
bounds. Limit block size to 2 MiB

Cc: Marvin Häuser <mhaeuser at posteo.de>
Cc: Pedro Falcato <pedro.falcato at gmail.com>
Cc: Vitaly Cheptsov <vit9696 at protonmail.com>
Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
Signed-off-by: Savva Mitrofanov <savvamtr at gmail.com>
---
 Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h    | 14 ++++++++++++++
 Features/Ext4Pkg/Ext4Dxe/Superblock.c |  5 +++++
 2 files changed, 19 insertions(+)

diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
index 2e489ce4dd86..a23323319a59 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
+++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
@@ -40,6 +40,20 @@
 #define EXT4_EFI_PATH_MAX    4096

 #define EXT4_DRIVER_VERSION  0x0000

 

+//

+// The EXT4 Specification doesn't strictly limit block size and this value could be up to 2^31,

+// but in practice it is limited by PAGE_SIZE due to performance significant impact.

+// Many EXT4 implementations have size of block limited to PAGE_SIZE. In many cases it's limited

+// to 4096, which is a commonly supported page size on most MMU-capable hardware, and up to 65536.

+// So, to take a balance between compatibility and security measures, it is decided to use the

+// value of 2MiB as the limit, which is equal to page size on new hardware.

+// As for supporting big block sizes, EXT4 has a RO_COMPAT_FEATURE called BIGALLOC, which changes

+// EXT4 to use clustered allocation, so that each bit in the ext4 block allocation bitmap addresses

+// a power of two number of blocks. So it would be wiser to implement and use this feature

+// if there is such a need instead of big block size.

+//

+#define EXT4_LOG_BLOCK_SIZE_MAX  11

+

 /**

    Opens an ext4 partition and installs the Simple File System protocol.

 

diff --git a/Features/Ext4Pkg/Ext4Dxe/Superblock.c b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
index be3527e4d618..3f56de93c105 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Superblock.c
+++ b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
@@ -248,6 +248,11 @@ Ext4OpenSuperblock (
     return EFI_VOLUME_CORRUPTED;

   }

 

+  if (Sb->s_log_block_size > EXT4_LOG_BLOCK_SIZE_MAX) {

+    DEBUG ((DEBUG_ERROR, "[ext4] SuperBlock s_log_block_size %lu is too big\n", Sb->s_log_block_size));

+    return EFI_UNSUPPORTED;

+  }

+

   Partition->BlockSize = (UINT32)LShiftU64 (1024, Sb->s_log_block_size);

 

   // The size of a block group can also be calculated as 8 * Partition->BlockSize

-- 
2.39.0



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