4.20-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 3cc31fa65d85610574c0f6a474e89f4c419923d5 ]
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 --- fs/iomap.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/iomap.c b/fs/iomap.c index d6bc98ae8d35..ce837d962d47 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -492,16 +492,29 @@ 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))