From 42ea907d785d522e5ae661c3774b8a801ac7f00b Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Mon, 12 Oct 2015 17:21:25 +0100 Subject: [PATCH] staging: comedi: allow buffer wraparound in comedi_read() `comedi_read()` copies data from the acquisition data buffer, which is cyclic, to the user buffer using a single call to `copy_to_user()`. It currently avoids having to deal with wraparound of the cyclic buffer by limiting the amount it copies (and the amount returned to the user). Change it to deal with the wraparound using two calls to `copy_to_user()` if necessary. Signed-off-by: Ian Abbott Reviewed-by: H Hartley Sweeten Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/comedi_fops.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index f39448a0d301..a979f621f932 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -2491,11 +2491,11 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes, add_wait_queue(&async->wait_head, &wait); while (nbytes > 0 && !retval) { + unsigned int rp, n1, n2; + set_current_state(TASK_INTERRUPTIBLE); m = comedi_buf_read_n_available(s); - if (async->buf_read_ptr + m > async->prealloc_bufsz) - m = async->prealloc_bufsz - async->buf_read_ptr; n = min_t(size_t, m, nbytes); if (n == 0) { @@ -2532,8 +2532,14 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes, } continue; } - m = copy_to_user(buf, async->prealloc_buf + - async->buf_read_ptr, n); + rp = async->buf_read_ptr; + n1 = min(n, async->prealloc_bufsz - rp); + n2 = n - n1; + m = copy_to_user(buf, async->prealloc_buf + rp, n1); + if (m) + m += n2; + else if (n2) + m = copy_to_user(buf + n1, async->prealloc_buf, n2); if (m) { n -= m; retval = -EFAULT; -- 2.20.1