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Commit 3cc31fa6 authored by Eric Sandeen's avatar Eric Sandeen Committed by Darrick J. Wong
Browse files

iomap: don't search past page end in iomap_is_partially_uptodate 



iomap_is_partially_uptodate() is intended to check wither blocks within
the selected range of a not-uptodate page are uptodate; if the range we
care about is up to date, it's an optimization.

However, the iomap implementation continues to check all blocks up to
from+count, which is beyond the page, and can even be well beyond the
iop->uptodate bitmap.

I think the worst that will happen is that we may eventually find a zero
bit and return "not partially uptodate" when it would have otherwise
returned true, and skip the optimization.  Still, it's clearly an invalid
memory access that must be fixed.

So: fix this by limiting the search to within the page as is done in the
non-iomap variant, block_is_partially_uptodate().

Zorro noticed thiswhen KASAN went off for 512 byte blocks on a 64k
page system:

 BUG: KASAN: slab-out-of-bounds in iomap_is_partially_uptodate+0x1a0/0x1e0
 Read of size 8 at addr ffff800120c3a318 by task fsstress/22337

Reported-by: default avatarZorro Lang <zlang@redhat.com>
Signed-off-by: default avatarEric Sandeen <sandeen@redhat.com>
Signed-off-by: default avatarEric Sandeen <sandeen@sandeen.net>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent 7566ec39

fs/iomap.c

+15 −2
Original line number Diff line number Diff line
@@ -499,16 +499,29 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages, 
}

EXPORT_SYMBOL_GPL(iomap_readpages);



/*

 * iomap_is_partially_uptodate checks whether blocks within a page are

 * uptodate or not.

 *

 * Returns true if all blocks which correspond to a file portion

 * we want to read within the page are uptodate.

 */

int

iomap_is_partially_uptodate(struct page *page, unsigned long from,

		unsigned long count)

{

	struct iomap_page *iop = to_iomap_page(page);

	struct inode *inode = page->mapping->host;

	unsigned first = from >> inode->i_blkbits;

	unsigned last = (from + count - 1) >> inode->i_blkbits;

	unsigned len, first, last;

	unsigned i;



	/* Limit range to one page */

	len = min_t(unsigned, PAGE_SIZE - from, count);



	/* First and last blocks in range within page */

	first = from >> inode->i_blkbits;

	last = (from + len - 1) >> inode->i_blkbits;



	if (iop) {

		for (i = first; i <= last; i++)

			if (!test_bit(i, iop->uptodate))