io_uring/uring_cmd: switch sqe to async_data on EAGAIN

5eff57fa9f3a ("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: 5eff57fa9f3a ("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>

diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index cfb22e1de0e757112e73799c3a6806aa450295ac..bcfca18395c4c8c9d1316aa401d01b0c7890ad6a 100644 (file)
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -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;
+       ioucmd->sqe = sqe;
+       /* 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;