[PATCH] io_uring/rsrc: ensure segments counts are correct on kbuf buffers

[Jens Axboe <axboe@kernel.dk>]

kbuf imports have the front offset adjusted and segments removed, but
the tail segments are still included in the segment count that gets
passed in the iov_iter. As the segments aren't necessarily all the
same size, move importing to a separate helper and iterate the
mapped length to get an exact count.

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

---

Same as the one I sent out yesterday, but just for the kbuf part.

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 4099b8225670..04e19689d2f3 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1032,6 +1032,26 @@ static int validate_fixed_range(u64 buf_addr, size_t len,
 	return 0;
 }
 
+static int io_import_kbuf(int ddir, struct iov_iter *iter,
+			  struct io_mapped_ubuf *imu, size_t len, size_t offset)
+{
+	size_t count = len + offset;
+
+	iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, count);
+	iov_iter_advance(iter, offset);
+
+	if (count < imu->len) {
+		const struct bio_vec *bvec = iter->bvec;
+
+		while (len > bvec->bv_len) {
+			len -= bvec->bv_len;
+			bvec++;
+		}
+		iter->nr_segs = 1 + bvec - iter->bvec;
+	}
+	return 0;
+}
+
 static int io_import_fixed(int ddir, struct iov_iter *iter,
 			   struct io_mapped_ubuf *imu,
 			   u64 buf_addr, size_t len)
@@ -1052,11 +1072,8 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
 
 	offset = buf_addr - imu->ubuf;
 
-	if (imu->is_kbuf) {
-		iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, offset + len);
-		iov_iter_advance(iter, offset);
-		return 0;
-	}
+	if (imu->is_kbuf)
+		return io_import_kbuf(ddir, iter, imu, len, offset);
 
 	/*
 	 * Don't use iov_iter_advance() here, as it's really slow for

-- 
Jens Axboe