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staging: comedi: avoid bad truncation of a size_t in comedi_write()

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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: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2015-11-18 17:55:07 +00:00 committed by Greg Kroah-Hartman
parent 84a185ec42
commit 591c5f8a59
1 changed files with 5 additions and 8 deletions
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13
drivers/staging/comedi/comedi_fops.c
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@ -2357,16 +2357,13 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
break;
}
n = nbytes;
m = n;
/* Allocate all free buffer space. */
comedi_buf_write_alloc(s, async->prealloc_bufsz);
m = comedi_buf_write_n_allocated(s);
/* Avoid buffer wraparound. */
if (async->buf_write_ptr + m > async->prealloc_bufsz)
m = async->prealloc_bufsz - async->buf_write_ptr;
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;
n = min_t(size_t, m, nbytes);
if (n == 0) {
if (file->f_flags & O_NONBLOCK) {