[PATCH] Fix nasty 32-bit overflow bug in buffer i/o code.

[Anton Altaparmakov]

Any code that uses __getblk() and thus bread(), breadahead(), sb_bread(), 
sb_breadahead(), sb_getblk(), and calls it using a 64-bit block on a 
32-bit arch (where "long" is 32-bit) causes an inifinite loop in 
__getblk_slow() with an infinite stream of errors logged to dmesg like 
this:

__find_get_block_slow() failed. block=6740375944, b_blocknr=2445408648
b_state=0x00000020, b_size=512
device sda1 blocksize: 512

Note how in hex block is 0x191C1F988 and b_blocknr is 0x91C1F988 i.e. the 
top 32-bits are missing (in this case the 0x1 at the top).

This is because grow_dev_page() was broken in commit 676ce6d5ca30: "block: 
replace __getblk_slow misfix by grow_dev_page fix" by Hugh Dickins so that 
it now has a 32-bit overflow due to shifting the block value to the right 
so it fits in 32-bits and storing the result in pgoff_t variable which is 
32-bit and then passing the pgoff_t variable left-shifted as the block 
number which causes the top bits to get lost as the pgoff_t is not type 
cast to sector_t / 64-bit before the shift.

This patch fixes this issue by type casting "index" to sector_t before 
doing the left shift.

Note this is not a theoretical bug but has been seen in the field on a 
4TiB hard drive with logical sector size 512 bytes.

This patch has been verified to fix the infinite loop problem on 3.17-rc5 
kernel using a 4TB disk image mounted using "-o loop".  Without this patch 
doing a "find /nt" where /nt is an NTFS volume causes the inifinite loop 
100% reproducibly whilst with the patch it works fine as expected.

Signed-off-by: Anton Altaparmakov <aia21@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 3.6 3.8 3.10 3.12 3.14 3.16
---

Linus, can you please apply this?  Alternatively, Andrew, can you please 
pick this up and send it to Linus?

It would be good it it can be applied for 3.17 as well as to all stable 
kernels >= 3.6 as they are all broken!

Thanks a lot in advance!

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/

diff --git a/fs/buffer.c b/fs/buffer.c
index 8f05111..3588a80 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1022,7 +1022,8 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 		bh = page_buffers(page);
 		if (bh->b_size == size) {
 			end_block = init_page_buffers(page, bdev,
-						index << sizebits, size);
+						(sector_t)index << sizebits,
+						size);
 			goto done;
 		}
 		if (!try_to_free_buffers(page))
@@ -1043,7 +1044,8 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 	 */
 	spin_lock(&inode->i_mapping->private_lock);
 	link_dev_buffers(page, bh);
-	end_block = init_page_buffers(page, bdev, index << sizebits, size);
+	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
+			size);
 	spin_unlock(&inode->i_mapping->private_lock);
 done:
 	ret = (block < end_block) ? 1 : -ENXIO;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/