regmap: debugfs: Ensure we don't underflow when printing access masks

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>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index a3530dadb163e8c21bb251fcd89558040e62cafd..c11e72f7ab516699b89db42dd835f416a556d509 100644 (file)
--- 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 */