On 09/04/2021 15:49, Pavel Begunkov wrote:

On 01/04/2021 08:18, yangerkun wrote:

quoted

We get a bug:

BUG: KASAN: slab-out-of-bounds in iov_iter_revert+0x11c/0x404
lib/iov_iter.c:1139
Read of size 8 at addr ffff0000d3fb11f8 by task

CPU: 0 PID: 12582 Comm: syz-executor.2 Not tainted
5.10.0-00843-g352c8610ccd2 #2
Hardware name: linux,dummy-virt (DT)
Call trace:

...

quoted

 __asan_load8+0xb4/0xbc mm/kasan/generic.c:252
 iov_iter_revert+0x11c/0x404 lib/iov_iter.c:1139
 io_read fs/io_uring.c:3421 [inline]
 io_issue_sqe+0x2344/0x2d64 fs/io_uring.c:5943
 __io_queue_sqe+0x19c/0x520 fs/io_uring.c:6260
 io_queue_sqe+0x2a4/0x590 fs/io_uring.c:6326
 io_submit_sqe fs/io_uring.c:6395 [inline]
 io_submit_sqes+0x4c0/0xa04 fs/io_uring.c:6624

...

quoted

blkdev_read_iter can truncate iov_iter's count since the count + pos may
exceed the size of the blkdev. This will confuse io_read that we have
consume the iovec. And once we do the iov_iter_revert in io_read, we
will trigger the slab-out-of-bounds. Fix it by reexpand the count with
size has been truncated.

Looks right,

Acked-by: Pavel Begunkov <redacted>

Fwiw, we need to forget to drag it through 5.13 + stable

quoted

blkdev_write_iter can trigger the problem too.

Signed-off-by: yangerkun <redacted>
---
 fs/block_dev.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 92ed7d5df677..788e1014576f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c

@@ -1680,6 +1680,7 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	struct inode *bd_inode = bdev_file_inode(file);
 	loff_t size = i_size_read(bd_inode);
 	struct blk_plug plug;
+	size_t shorted = 0;
 	ssize_t ret;
 
 	if (bdev_read_only(I_BDEV(bd_inode)))

@@ -1697,12 +1698,17 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if ((iocb->ki_flags & (IOCB_NOWAIT | IOCB_DIRECT)) == IOCB_NOWAIT)
 		return -EOPNOTSUPP;
 
-	iov_iter_truncate(from, size - iocb->ki_pos);
+	size -= iocb->ki_pos;
+	if (iov_iter_count(from) > size) {
+		shorted = iov_iter_count(from) - size;
+		iov_iter_truncate(from, size);
+	}
 
 	blk_start_plug(&plug);
 	ret = __generic_file_write_iter(iocb, from);
 	if (ret > 0)
 		ret = generic_write_sync(iocb, ret);
+	iov_iter_reexpand(from, iov_iter_count(from) + shorted);
 	blk_finish_plug(&plug);
 	return ret;
 }

@@ -1714,13 +1720,21 @@ ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	struct inode *bd_inode = bdev_file_inode(file);
 	loff_t size = i_size_read(bd_inode);
 	loff_t pos = iocb->ki_pos;
+	size_t shorted = 0;
+	ssize_t ret;
 
 	if (pos >= size)
 		return 0;
 
 	size -= pos;
-	iov_iter_truncate(to, size);
-	return generic_file_read_iter(iocb, to);
+	if (iov_iter_count(to) > size) {
+		shorted = iov_iter_count(to) - size;
+		iov_iter_truncate(to, size);
+	}
+
+	ret = generic_file_read_iter(iocb, to);
+	iov_iter_reexpand(to, iov_iter_count(to) + shorted);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(blkdev_read_iter);
 

-- 
Pavel Begunkov