io_uring: improve import_fixed overflow checks

Replace a hand-coded overflow check with a specialised function. Even
though compilers are smart enough to generate identical binary (i.e.
check carry bit), but it's more foolproof and conveys the intention
better.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/e437dcdc929bacbb6f11a4824ecbbf17225cb82a.1617287883.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 f53d932..e6508b1 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2785,8 +2785,8 @@ static int io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter)
        size_t len = req->rw.len;
        struct io_mapped_ubuf *imu;
        u16 index, buf_index = req->buf_index;
+       u64 buf_end, buf_addr = req->rw.addr;
        size_t offset;
-       u64 buf_addr;
 
        if (unlikely(buf_index >= ctx->nr_user_bufs))
                return -EFAULT;
@@ -2794,11 +2794,10 @@ static int io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter)
        imu = &ctx->user_bufs[index];
        buf_addr = req->rw.addr;
 
-       /* overflow */
-       if (buf_addr + len < buf_addr)
+       if (unlikely(check_add_overflow(buf_addr, (u64)len, &buf_end)))
                return -EFAULT;
        /* not inside the mapped region */
-       if (buf_addr < imu->ubuf || buf_addr + len > imu->ubuf + imu->len)
+       if (buf_addr < imu->ubuf || buf_end > imu->ubuf + imu->len)
                return -EFAULT;
 
        /*