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

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At one point in `comedi_read()`, the variable `n` gets assigned to the
minimum of the parameter `nbytes` and the amount of readable buffer
space `m`.  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 2015-10-12 17:21:24 +01:00 committed by Greg Kroah-Hartman
parent 76e8e7d4ff
commit 8ea939284d
1 changed files with 1 additions and 4 deletions
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5
drivers/staging/comedi/comedi_fops.c
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@ -2493,13 +2493,10 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
while (nbytes > 0 && !retval) {
set_current_state(TASK_INTERRUPTIBLE);
n = nbytes;
m = comedi_buf_read_n_available(s);
if (async->buf_read_ptr + m > async->prealloc_bufsz)
m = async->prealloc_bufsz - async->buf_read_ptr;
if (m < n)
n = m;
n = min_t(size_t, m, nbytes);
if (n == 0) {
unsigned runflags = comedi_get_subdevice_runflags(s);