From b763ec17ac762470eec5be8ebcc43e4f8b2c2b82 Mon Sep 17 00:00:00 2001
From: Mark Brown <broonie@kernel.org>
Date: Sat, 19 Sep 2015 07:00:18 -0700
Subject: regmap: debugfs: Ensure we don't underflow when printing access masks

From: Mark Brown <broonie@kernel.org>

commit b763ec17ac762470eec5be8ebcc43e4f8b2c2b82 upstream.

If a read is attempted which is smaller than the line length then we may
underflow the subtraction we're doing with the unsigned size_t type so
move some of the calculation to be additions on the right hand side
instead in order to avoid this.

Reported-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/base/regmap/regmap-debugfs.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/base/regmap/regmap-debugfs.c
+++ b/drivers/base/regmap/regmap-debugfs.c
@@ -432,7 +432,7 @@ static ssize_t regmap_access_read_file(s
 		/* If we're in the region the user is trying to read */
 		if (p >= *ppos) {
 			/* ...but not beyond it */
-			if (buf_pos >= count - 1 - tot_len)
+			if (buf_pos + tot_len + 1 >= count)
 				break;
 
 			/* Format the register */