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Commit 591c5f8a authored by Ian Abbott's avatar Ian Abbott Committed by Greg Kroah-Hartman
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staging: comedi: avoid bad truncation of a size_t in comedi_write() 



At one point in `comedi_write()`, the variable `n` gets assigned to the
minimum of the parameter `nbytes` and the amount of writeable buffer
space.  The way that is done currently is unsafe in the unlikely case
that `nbytes` exceeds `UINT_MAX`, so fix it.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Reviewed-by: default avatarH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 84a185ec

drivers/staging/comedi/comedi_fops.c

+5 −8
Original line number Diff line number Diff line
@@ -2357,16 +2357,13 @@ static ssize_t comedi_write(struct file *file, const char __user *buf, 
			break;

		}



		n = nbytes;



		m = n;

		if (async->buf_write_ptr + m > async->prealloc_bufsz)

			m = async->prealloc_bufsz - async->buf_write_ptr;

		/* Allocate all free buffer space. */

		comedi_buf_write_alloc(s, async->prealloc_bufsz);

		if (m > comedi_buf_write_n_allocated(s))

		m = comedi_buf_write_n_allocated(s);

		if (m < n)

			n = m;

		/* Avoid buffer wraparound. */

		if (async->buf_write_ptr + m > async->prealloc_bufsz)

			m = async->prealloc_bufsz - async->buf_write_ptr;

		n = min_t(size_t, m, nbytes);



		if (n == 0) {

			if (file->f_flags & O_NONBLOCK) {