[34-longterm 193/196] fs/partitions/efi.c: corrupted GUID partition tables can cause kernel oops

[Paul Gortmaker]

From: Timo Warns <Warns@xxxxxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 3eb8e74ec72736b9b9d728bad30484ec89c91dde upstream.

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@xxxxxxxxxxxxxxxxxxxx: fix layout and indenting]
[PG: replace state->bdev with bdev, since 1493bf217f7f isn't in 34]

Signed-off-by: Timo Warns <warns@xxxxxxxxxxxx>
Cc: Matt Domsch <Matt_Domsch@xxxxxxxx>
Cc: Eugene Teo <eugeneteo@xxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 fs/partitions/efi.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/partitions/efi.c b/fs/partitions/efi.c
index ee59684..9b40337 100644
--- a/fs/partitions/efi.c
+++ b/fs/partitions/efi.c
@@ -312,6 +312,15 @@ is_gpt_valid(struct block_device *bdev, u64 lba,
 		goto fail;
 	}
 
+	/* Check the GUID Partition Table header size */
+	if (le32_to_cpu((*gpt)->header_size) >
+			bdev_logical_block_size(bdev)) {
+		pr_debug("GUID Partition Table Header size is wrong: %u > %u\n",
+			le32_to_cpu((*gpt)->header_size),
+			bdev_logical_block_size(bdev));
+		goto fail;
+	}
+
 	/* Check the GUID Partition Table CRC */
 	origcrc = le32_to_cpu((*gpt)->header_crc32);
 	(*gpt)->header_crc32 = 0;
-- 
1.7.9.3

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