Missing check for wrong s_log_block_size exponent leads to shift out of
bounds. Limit block size to 2 MiB
Cc: Marvin Häuser <mhaeu...@posteo.de>
Cc: Pedro Falcato <pedro.falc...@gmail.com>
Cc: Vitaly Cheptsov <vit9...@protonmail.com>
Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
Signed-off-by: Savva Mitrofanov <savva...@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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