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iomap: don't search past page end in iomap_is_partially_uptodate

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[ Upstream commit 3cc31fa65d ]

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: Zorro Lang <zlang@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Eric Sandeen 2018-12-21 08:42:50 -08:00 committed by Greg Kroah-Hartman
parent 00886cebcc
commit c9dcb871b1
1 changed files with 15 additions and 2 deletions
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17
fs/iomap.c
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@ -488,16 +488,29 @@ 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))