io_uring/kbuf: fix missing BUF_MORE for incremental buffers at EOF

For a zero length transfer, io_kbuf_inc_commit() is called with !len.
Since we never enter the while loop to consume the buffers,
io_kbuf_inc_commit() ends up returning true, consuming the buffer. But
if no data was consumed, by definition it cannot have consumed the
buffer. Return false for that case.

Reported-by: Martin Michaelis <code@mgjm.de>
Cc: stable@vger.kernel.org
Fixes: ae98dbf43d75 ("io_uring/kbuf: add support for incremental buffer consumption")
Link: https://github.com/axboe/liburing/issues/1553
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index e7f444953dfb3d5ff8834f6894ab109c09c5a4cd..a4cb6752b7aa6e99fc4b014d02a53f31c7aa5fdb 100644 (file)
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -34,6 +34,10 @@ struct io_provide_buf {
 
 static bool io_kbuf_inc_commit(struct io_buffer_list *bl, int len)
 {
+       /* No data consumed, return false early to avoid consuming the buffer */
+       if (!len)
+               return false;
+
        while (len) {
                struct io_uring_buf *buf;
                u32 buf_len, this_len;