linux-kernel - RE: [PATCH] block: create ioctl to discard-or-zeroout a range of blocks

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Date:	Fri, 13 Nov 2015 03:36:21 +0000
From:	"Seymour, Shane M" <shane.seymour@....com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>
Subject: RE: [PATCH] block: create ioctl to discard-or-zeroout a range of
 blocks

> I don't have a device large enough to test for signedness errors, since passing 
> huge values for start and len never make it past the i_size_read check.

If you have someone trying to bypass your sanity checks then if start=18446744073709551104 and len=1024 the result of adding them together will be 512 (subtracting an extra 1 in the patched code to get 511 for end). That will pass the i_size_read check won't it? If so that would cause lstart in truncate_inode_pages_range() to be -512. I don't know what truncate_inode_pages_range() will do with a negative lstart value like that but it seems like an unusual value for your code to be willing to pass into truncate_inode_pages_range().

Shane
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