Commit 3cc31fa6 authored Dec 21, 2018 by Eric Sandeen Committed by Darrick J. Wong Dec 21, 2018

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: 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>

parent 7566ec39

fs/iomap.c

+15 −2

Original line number	Diff line number	Diff line
		@@ -499,16 +499,29 @@ done:
		}
		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))

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