[PATCH 7.2 17/82] io_uring/cmd: fix iovec leak when the async cmd is not recycled

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Woraphat Khiaodaeng <[email protected]>

commit bb34ae5da3365699d53a756f4c96b6ea9f8ba0c1 upstream.

An io_async_cmd carries an iovec array in ->vec.iovec, allocated when the
vec has to grow and kept across recycling through ctx->cmd_cache.  On two
paths nothing frees it and io_clean_op()'s kfree(req->async_data) drops
the io_async_cmd without it.

io_req_uring_cleanup() clears the async data flags only when
io_alloc_cache_put() succeeds, and the cache holds IO_ALLOC_CACHE_MAX ==
128 entries, so once it is full the put fails and the vec is left behind.
An NVMe passthrough workload gets there without doing anything unusual:
nvme_uring_cmd_io() returns -EIOCBQUEUED, so the io_async_cmd stays
attached for the lifetime of the command and the live object count tracks
the queue depth.  Above 128 the puts start failing.

->cleanup is the last chance to free an inherited vec, since
io_req_uring_cleanup() returns early for an io-wq issued command and is
not called at all for one completed without ever being issued.  But
io_clean_op() calls ->cleanup only if REQ_F_NEED_CLEANUP is set, and for
uring_cmd that happens only where the vec has to grow, so a command
reusing a large enough cached vec never sets it.  io_rw_alloc_async() and
io_msg_alloc_async() flag an inherited vec for exactly this reason;
io_uring_cmd_prep() does not.

Flag an inherited vec in io_uring_cmd_prep(), and free the vec when the
cache put fails, as io_req_rw_cleanup() does.

The leak is invisible under KASAN, where io_alloc_cache_vec_kasan() frees
the vec unconditionally.

Fixes: 3a4689ac109f ("io_uring/cmd: add iovec cache for commands")
Cc: [email protected]
Signed-off-by: Woraphat Khiaodaeng <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 io_uring/uring_cmd.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -38,6 +38,8 @@ static void io_req_uring_cleanup(struct
 	if (io_alloc_cache_put(&req->ctx->cmd_cache, ac)) {
 		ioucmd->sqe = NULL;
 		io_req_async_data_clear(req, REQ_F_NEED_CLEANUP);
+	} else {
+		io_vec_free(&ac->vec);
 	}
 }
 
@@ -208,6 +210,8 @@ int io_uring_cmd_prep(struct io_kiocb *r
 	ac = io_uring_alloc_async_data(&req->ctx->cmd_cache, req);
 	if (!ac)
 		return -ENOMEM;
+	if (ac->vec.iovec)
+		req->flags |= REQ_F_NEED_CLEANUP;
 	ioucmd->sqe = sqe;
 	return 0;
 }