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.

[akpm@linux-foundation.org: fix layout and indenting]
Signed-off-by: Timo Warns <warns@pre-sense.de>
Cc: Matt Domsch <Matt_Domsch@dell.com>
Cc: Eugene Teo <eugeneteo@kernel.sg>
Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[ WT: no bdev_logical_block_size() in 2.4, use get_hardsect_size() instead ]
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/fs/partitions/efi.c b/fs/partitions/efi.c
index 5f3ab44..c869f47 100644
--- a/fs/partitions/efi.c
+++ b/fs/partitions/efi.c
@@ -337,6 +337,7 @@
 	     gpt_header **gpt, gpt_entry **ptes)
 {
 	u32 crc, origcrc;
+	int blocksize;
 
 	if (!hd || !bdev || !gpt || !ptes)
 		return 0;
@@ -353,6 +354,19 @@
 		return 0;
 	}
 
+	/* Check the GUID Partition Table header size */
+	blocksize = get_hardsect_size(to_kdev_t(bdev->bd_dev));
+	if (!blocksize)
+		blocksize = 512;
+
+	if (le32_to_cpu((*gpt)->header_size) > blocksize) {
+		Dprintk("GUID Partition Table Header size is wrong: %u > %u\n",
+			le32_to_cpu((*gpt)->header_size), blocksize);
+		kfree(*gpt);
+		*gpt = NULL;
+		return 0;
+	}
+
 	/* Check the GUID Partition Table CRC */
 	origcrc = le32_to_cpu((*gpt)->header_crc32);
 	(*gpt)->header_crc32 = 0;