io_uring: fix NULL reg-buffer

io_import_fixed() doesn't expect a registered buffer slot to be NULL and
would fail stumbling on it. We don't allow it, but if during
__io_sqe_buffers_update() rsrc removal succeeds but following register
fails, we'll get such a situation.

Do it atomically and don't remove buffers until we sure that a new one
can be set.

Fixes: 634d00df5e1cf ("io_uring: add full-fledged dynamic buffers support")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/830020f9c387acddd51962a3123b5566571b8c6d.1619446608.git.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 6b578c3..863420e 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8419,7 +8419,6 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 {
        u64 __user *tags = u64_to_user_ptr(up->tags);
        struct iovec iov, __user *iovs = u64_to_user_ptr(up->data);
-       struct io_mapped_ubuf *imu;
        struct page *last_hpage = NULL;
        bool needs_switch = false;
        __u32 done;
@@ -8431,6 +8430,8 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
                return -EINVAL;
 
        for (done = 0; done < nr_args; done++) {
+               struct io_mapped_ubuf *imu;
+               int offset = up->offset + done;
                u64 tag = 0;
 
                err = io_copy_iov(ctx, &iov, iovs, done);
@@ -8440,28 +8441,27 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
                        err = -EFAULT;
                        break;
                }
+               err = io_buffer_validate(&iov);
+               if (err)
+                       break;
+               err = io_sqe_buffer_register(ctx, &iov, &imu, &last_hpage);
+               if (err)
+                       break;
 
-               i = array_index_nospec(up->offset + done, ctx->nr_user_bufs);
-               imu = ctx->user_bufs[i];
-               if (imu) {
-                       err = io_queue_rsrc_removal(ctx->buf_data, up->offset + done,
-                                                   ctx->rsrc_node, imu);
-                       if (err)
+               i = array_index_nospec(offset, ctx->nr_user_bufs);
+               if (ctx->user_bufs[i]) {
+                       err = io_queue_rsrc_removal(ctx->buf_data, offset,
+                                                   ctx->rsrc_node, ctx->user_bufs[i]);
+                       if (unlikely(err)) {
+                               io_buffer_unmap(ctx, &imu);
                                break;
+                       }
                        ctx->user_bufs[i] = NULL;
                        needs_switch = true;
                }
 
-               if (iov.iov_base || iov.iov_len) {
-                       err = io_buffer_validate(&iov);
-                       if (err)
-                               break;
-                       err = io_sqe_buffer_register(ctx, &iov, &ctx->user_bufs[i],
-                                                    &last_hpage);
-                       if (err)
-                               break;
-                       ctx->buf_data->tags[up->offset + done] = tag;
-               }
+               ctx->user_bufs[i] = imu;
+               ctx->buf_data->tags[offset] = tag;
        }
 
        if (needs_switch)