io_uring: handle multiple personalities in link chains

If we have a chain of requests and they don't all use the same
credentials, then the head of the chain will be issued with the
credentails of the tail of the chain.

Ensure __io_queue_sqe() overrides the credentials, if they are different.

Once we do that, we can clean up the creds handling as well, by only
having io_submit_sqe() do the lookup of a personality. It doesn't need
to assign it, since __io_queue_sqe() now always does the right thing.

Fixes: 75c6a03904e0 ("io_uring: support using a registered personality for commands")
Reported-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index de650df..7d0be26 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4705,11 +4705,21 @@ static void __io_queue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
        struct io_kiocb *linked_timeout;
        struct io_kiocb *nxt = NULL;
+       const struct cred *old_creds = NULL;
        int ret;
 
 again:
        linked_timeout = io_prep_linked_timeout(req);
 
+       if (req->work.creds && req->work.creds != current_cred()) {
+               if (old_creds)
+                       revert_creds(old_creds);
+               if (old_creds == req->work.creds)
+                       old_creds = NULL; /* restored original creds */
+               else
+                       old_creds = override_creds(req->work.creds);
+       }
+
        ret = io_issue_sqe(req, sqe, &nxt, true);
 
        /*
@@ -4759,6 +4769,8 @@ done_req:
                        goto punt;
                goto again;
        }
+       if (old_creds)
+               revert_creds(old_creds);
 }
 
 static void io_queue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe)
@@ -4803,7 +4815,6 @@ static inline void io_queue_link_head(struct io_kiocb *req)
 static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                          struct io_submit_state *state, struct io_kiocb **link)
 {
-       const struct cred *old_creds = NULL;
        struct io_ring_ctx *ctx = req->ctx;
        unsigned int sqe_flags;
        int ret, id;
@@ -4818,14 +4829,12 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 
        id = READ_ONCE(sqe->personality);
        if (id) {
-               const struct cred *personality_creds;
-
-               personality_creds = idr_find(&ctx->personality_idr, id);
-               if (unlikely(!personality_creds)) {
+               req->work.creds = idr_find(&ctx->personality_idr, id);
+               if (unlikely(!req->work.creds)) {
                        ret = -EINVAL;
                        goto err_req;
                }
-               old_creds = override_creds(personality_creds);
+               get_cred(req->work.creds);
        }
 
        /* same numerical values with corresponding REQ_F_*, safe to copy */
@@ -4837,8 +4846,6 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 err_req:
                io_cqring_add_event(req, ret);
                io_double_put_req(req);
-               if (old_creds)
-                       revert_creds(old_creds);
                return false;
        }
 
@@ -4899,8 +4906,6 @@ err_req:
                }
        }
 
-       if (old_creds)
-               revert_creds(old_creds);
        return true;
 }