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Ext4Pkg: Fix shift out of bounds in Ext4OpenSuperblock

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

Signed-off-by: Savva Mitrofanov <savvamtr@gmail.com>
This commit is contained in:
Savva Mitrofanov 2022-10-28 18:09:37 +06:00
parent 17fa176e4d
commit ed668ba596
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2 changed files with 19 additions and 0 deletions
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14
Ext4Pkg/Ext4Dxe/Ext4Dxe.h
View File

@ -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.

5
Ext4Pkg/Ext4Dxe/Superblock.c
View File

@ -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