io_uring: support using a registered personality for commandsfor-5.6/io_uring-vfs-creds

For personalities previously registered via IORING_REGISTER_PERSONALITY,
allow any command to select them. This is done through setting
sqe->personality to the id returned from registration, and then flagging
sqe->flags with IOSQE_PERSONALITY.

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

2 files changed, 32 insertions, 3 deletions

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 74185cbabc3d..95a450451782 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1188,6 +1188,8 @@ static void __io_req_aux_free(struct io_kiocb *req)
 		else
 			fput(req->file);
 	}
+	if (req->work.creds)
+		put_cred(req->work.creds);
 }
 
 static void __io_free_req(struct io_kiocb *req)
@@ -3975,7 +3977,8 @@ static int io_req_defer_prep(struct io_kiocb *req,
 		mmgrab(current->mm);
 		req->work.mm = current->mm;
 	}
-	req->work.creds = get_current_cred();
+	if (!req->work.creds)
+		req->work.creds = get_current_cred();
 
 	switch (req->opcode) {
 	case IORING_OP_NOP:
@@ -4605,11 +4608,13 @@ static inline void io_queue_link_head(struct io_kiocb *req)
 }
 
 #define SQE_VALID_FLAGS	(IOSQE_FIXED_FILE|IOSQE_IO_DRAIN|IOSQE_IO_LINK|	\
-				IOSQE_IO_HARDLINK | IOSQE_ASYNC)
+				IOSQE_IO_HARDLINK | IOSQE_ASYNC | \
+				IOSQE_PERSONALITY)
 
 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;
@@ -4621,6 +4626,18 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		ret = -EINVAL;
 		goto err_req;
 	}
+
+	if (sqe_flags & IOSQE_PERSONALITY) {
+		int id = READ_ONCE(sqe->personality);
+
+		req->work.creds = idr_find(&ctx->personality_idr, id);
+		if (unlikely(!req->work.creds)) {
+			ret = -EINVAL;
+			goto err_req;
+		}
+		old_creds = override_creds(req->work.creds);
+	}
+
 	/* same numerical values with corresponding REQ_F_*, safe to copy */
 	req->flags |= sqe_flags & (IOSQE_IO_DRAIN|IOSQE_IO_HARDLINK|
 					IOSQE_ASYNC);
@@ -4630,6 +4647,8 @@ 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;
 	}
 
@@ -4690,6 +4709,8 @@ err_req:
 		}
 	}
 
+	if (old_creds)
+		revert_creds(old_creds);
 	return true;
 }
 
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index b4ccf31db2d1..761abd5c197f 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -40,7 +40,12 @@ struct io_uring_sqe {
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	union {
-		__u16	buf_index;	/* index into fixed buffers, if used */
+		struct {
+			/* index into fixed buffers, if used */
+			__u16	buf_index;
+			/* personality to use, if used */
+			__u16	personality;
+		};
 		__u64	__pad2[3];
 	};
 };
@@ -51,6 +56,7 @@ enum {
 	IOSQE_IO_LINK_BIT,
 	IOSQE_IO_HARDLINK_BIT,
 	IOSQE_ASYNC_BIT,
+	IOSQE_PERSONALITY_BIT,
 };
 
 /*
@@ -66,6 +72,8 @@ enum {
 #define IOSQE_IO_HARDLINK	(1U << IOSQE_IO_HARDLINK_BIT)
 /* always go async */
 #define IOSQE_ASYNC		(1U << IOSQE_ASYNC_BIT)
+/* use specified personality */
+#define IOSQE_PERSONALITY	(1U << IOSQE_PERSONALITY_BIT)
 
 /*
  * io_uring_setup() flags