[PATCH 3.16.y-ckt 01/94] regmap: debugfs: Ensure we don't underflow when printing access masks

[Luis Henriques]

3.16.7-ckt20 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Brown <broonie at 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 at rasmusvillemoes.dk>
Signed-off-by: Mark Brown <broonie at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/base/regmap/regmap-debugfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index a3530dadb163..c11e72f7ab51 100644
--- 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(struct file *file,
 		/* 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 */