io_uring: fix races with buffer table unregister

Fixed buffer table quiesce might unlock ->uring_lock, potentially
letting new requests to be submitted, don't allow those requests to
use the table as they will race with unregistration.

Reported-and-tested-by: van fantasy <g1042620637@gmail.com>
Fixes: bd54b6fe3316ec ("io_uring: implement fixed buffers registration similar to fixed files")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 00d2667..be05f37 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -10680,12 +10680,19 @@ static void __io_sqe_buffers_unregister(struct io_ring_ctx *ctx)
 
 static int io_sqe_buffers_unregister(struct io_ring_ctx *ctx)
 {
+       unsigned nr = ctx->nr_user_bufs;
        int ret;
 
        if (!ctx->buf_data)
                return -ENXIO;
 
+       /*
+        * Quiesce may unlock ->uring_lock, and while it's not held
+        * prevent new requests using the table.
+        */
+       ctx->nr_user_bufs = 0;
        ret = io_rsrc_ref_quiesce(ctx->buf_data, ctx);
+       ctx->nr_user_bufs = nr;
        if (!ret)
                __io_sqe_buffers_unregister(ctx);
        return ret;