Commit e663da62 authored Feb 12, 2025 by Caleb Sander Mateos Committed by Jens Axboe Feb 12, 2025

io_uring/uring_cmd: switch sqe to async_data on EAGAIN



5eff57fa ("io_uring/uring_cmd: defer SQE copying until it's needed")
moved the unconditional memcpy() of the uring_cmd SQE to async_data
to 2 cases when the request goes async:
- If REQ_F_FORCE_ASYNC is set to force the initial issue to go async
- If ->uring_cmd() returns -EAGAIN in the initial non-blocking issue

Unlike the REQ_F_FORCE_ASYNC case, in the EAGAIN case, io_uring_cmd()
copies the SQE to async_data but neglects to update the io_uring_cmd's
sqe field to point to async_data. As a result, sqe still points to the
slot in the userspace-mapped SQ. At the end of io_submit_sqes(), the
kernel advances the SQ head index, allowing userspace to reuse the slot
for a new SQE. If userspace reuses the slot before the io_uring worker
reissues the original SQE, the io_uring_cmd's SQE will be corrupted.

Introduce a helper io_uring_cmd_cache_sqes() to copy the original SQE to
the io_uring_cmd's async_data and point sqe there. Use it for both the
REQ_F_FORCE_ASYNC and EAGAIN cases. This ensures the uring_cmd doesn't
read from the SQ slot after it has been returned to userspace.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Fixes: 5eff57fa ("io_uring/uring_cmd: defer SQE copying until it's needed")
Link: https://lore.kernel.org/r/20250212204546.3751645-3-csander@purestorage.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 34cae912

io_uring/uring_cmd.c

+14 −9

Original line number	Diff line number	Diff line
		@@ -168,6 +168,15 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, u64 res2,
		}
		EXPORT_SYMBOL_GPL(io_uring_cmd_done);

		static void io_uring_cmd_cache_sqes(struct io_kiocb *req)
		{
		struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
		struct io_uring_cmd_data *cache = req->async_data;

		memcpy(cache->sqes, ioucmd->sqe, uring_sqe_size(req->ctx));
		ioucmd->sqe = cache->sqes;
		}

		static int io_uring_cmd_prep_setup(struct io_kiocb *req,
		const struct io_uring_sqe *sqe)
		{
		@@ -179,14 +188,10 @@ static int io_uring_cmd_prep_setup(struct io_kiocb *req,
		return -ENOMEM;
		cache->op_data = NULL;

		if (!(req->flags & REQ_F_FORCE_ASYNC)) {
		/* defer memcpy until we need it */
		ioucmd->sqe = sqe;
		return 0;
		}

		memcpy(cache->sqes, sqe, uring_sqe_size(req->ctx));
		ioucmd->sqe = cache->sqes;
		/* defer memcpy until we need it */
		if (unlikely(req->flags & REQ_F_FORCE_ASYNC))
		io_uring_cmd_cache_sqes(req);
		return 0;
		}

		@@ -253,7 +258,7 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
		struct io_uring_cmd_data *cache = req->async_data;

		if (ioucmd->sqe != cache->sqes)
		memcpy(cache->sqes, ioucmd->sqe, uring_sqe_size(req->ctx));
		io_uring_cmd_cache_sqes(req);
		return -EAGAIN;
		} else if (ret == -EIOCBQUEUED) {
		return -EIOCBQUEUED;