linux-kernel - [PATCH 05/10] staging: comedi: avoid bad truncation of a size_t in comedi

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Message-Id: <1444666890-14353-6-git-send-email-abbotti@mev.co.uk>
Date:	Mon, 12 Oct 2015 17:21:24 +0100
From:	Ian Abbott <abbotti@....co.uk>
To:	driverdev-devel@...uxdriverproject.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ian Abbott <abbotti@....co.uk>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 05/10] staging: comedi: avoid bad truncation of a size_t in comedi_read()

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@....co.uk>
---
 drivers/staging/comedi/comedi_fops.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index ae9d519..d51c94c 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2492,13 +2492,10 @@ 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);
-- 
2.6.1

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