fs/partitions/efi.c: corrupted GUID partition tables can cause kernel…

… oops

The kernel automatically evaluates partition tables of storage devices.
The code for evaluating GUID partitions (in fs/partitions/efi.c) contains
a bug that causes a kernel oops on certain corrupted GUID partition
tables.

This bug has security impacts, because it allows, for example, to
prepare a storage device that crashes a kernel subsystem upon connecting
the device (e.g., a "USB Stick of (Partial) Death").

	crc = efi_crc32((const unsigned char *) (*gpt), le32_to_cpu((*gpt)->header_size));

computes a CRC32 checksum over gpt covering (*gpt)->header_size bytes.
There is no validation of (*gpt)->header_size before the efi_crc32 call.

A corrupted partition table may have large values for (*gpt)->header_size.
 In this case, the CRC32 computation access memory beyond the memory
allocated for gpt, which may cause a kernel heap overflow.

Validate value of GUID partition table header size.

[[email protected]: fix layout and indenting]
Signed-off-by: Timo Warns <[email protected]>
Cc: Matt Domsch <[email protected]>
Cc: Eugene Teo <[email protected]>
Cc: Dave Jones <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/partitions/efi.c

@@ -310,6 +310,15 @@ static int is_gpt_valid(struct parsed_partitions *state, u64 lba,
 		goto fail;
 	}
 
+	/* Check the GUID Partition Table header size */
+	if (le32_to_cpu((*gpt)->header_size) >
+			bdev_logical_block_size(state->bdev)) {
+		pr_debug("GUID Partition Table Header size is wrong: %u > %u\n",
+			le32_to_cpu((*gpt)->header_size),
+			bdev_logical_block_size(state->bdev));
+		goto fail;
+	}
+
 	/* Check the GUID Partition Table CRC */
 	origcrc = le32_to_cpu((*gpt)->header_crc32);
 	(*gpt)->header_crc32 = 0;