From 1939316bf988f3e49a07d9c4dd6f660bf4daa53d Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Mon, 28 Aug 2023 18:47:31 -0400
Subject: [PATCH] io_uring: kiocb_done() should *not* trust ->ki_pos if
->{read,write}_iter() failed
->ki_pos value is unreliable in such cases. For an obvious example,
consider O_DSYNC write - we feed the data to page cache and start IO,
then we make sure it's completed. Update of ->ki_pos is dealt with
by the first part; failure in the second ends up with negative value
returned _and_ ->ki_pos left advanced as if sync had been successful.
In the same situation write(2) does not advance the file position
at all.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
io_uring/rw.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/io_uring/rw.c b/io_uring/rw.c
index c8c822fa79805..08d94fb972f07 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -339,7 +339,7 @@ static int kiocb_done(struct io_kiocb *req, ssize_t ret,
struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
unsigned final_ret = io_fixup_rw_res(req, ret);
- if (req->flags & REQ_F_CUR_POS)
+ if (ret >= 0 && req->flags & REQ_F_CUR_POS)
req->file->f_pos = rw->kiocb.ki_pos;
if (ret >= 0 && (rw->kiocb.ki_complete == io_complete_rw)) {
if (!__io_complete_rw_common(req, ret)) {
--
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