[PATCH AUTOSEL 5.8 15/29] fuse: fix the ->direct_IO() treatment of iov_iter

Sasha Levin
2020-09-29T01:36:25Z

From: Al Viro <viro@zeniv.linux.org.uk>

[ Upstream commit 933a3752babcf6513117d5773d2b70782d6ad149 ]

the callers rely upon having any iov_iter_truncate() done inside
->direct_IO() countered by iov_iter_reexpand().

Reported-by: Qian Cai <cai@redhat.com>
Tested-by: Qian Cai <cai@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/fuse/file.c | 25 ++++++++++++-------------
1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 83d917f7e5425..98e170cc0b932 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -3091,11 +3091,10 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
ssize_t ret = 0;
struct file *file = iocb->ki_filp;
struct fuse_file *ff = file->private_data;
- bool async_dio = ff->fc->async_dio;
loff_t pos = 0;
struct inode *inode;
loff_t i_size;
- size_t count = iov_iter_count(iter);
+ size_t count = iov_iter_count(iter), shortened = 0;
loff_t offset = iocb->ki_pos;
struct fuse_io_priv *io;

@@ -3103,17 +3102,9 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
inode = file->f_mapping->host;
i_size = i_size_read(inode);

- if ((iov_iter_rw(iter) == READ) && (offset > i_size))
+ if ((iov_iter_rw(iter) == READ) && (offset >= i_size))
return 0;

- /* optimization for short read */
- if (async_dio && iov_iter_rw(iter) != WRITE && offset + count > i_size) {
- if (offset >= i_size)
- return 0;
- iov_iter_truncate(iter, fuse_round_up(ff->fc, i_size - offset));
- count = iov_iter_count(iter);
- }
-
io = kmalloc(sizeof(struct fuse_io_priv), GFP_KERNEL);
if (!io)
return -ENOMEM;
@@ -3129,15 +3120,22 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
* By default, we want to optimize all I/Os with async request
* submission to the client filesystem if supported.
*/
- io->async = async_dio;
+ io->async = ff->fc->async_dio;
io->iocb = iocb;
io->blocking = is_sync_kiocb(iocb);

+ /* optimization for short read */
+ if (io->async && !io->write && offset + count > i_size) {
+ iov_iter_truncate(iter, fuse_round_up(ff->fc, i_size - offset));
+ shortened = count - iov_iter_count(iter);
+ count -= shortened;
+ }
+
/*
* We cannot asynchronously extend the size of a file.
* In such case the aio will behave exactly like sync io.
*/
- if ((offset + count > i_size) && iov_iter_rw(iter) == WRITE)
+ if ((offset + count > i_size) && io->write)
io->blocking = true;

if (io->async && io->blocking) {
@@ -3155,6 +3153,7 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
} else {
ret = __fuse_direct_read(io, iter, &pos);
}
+ iov_iter_reexpand(iter, iov_iter_count(iter) + shortened);

if (io->async) {
bool blocking = io->blocking;
--
2.25.1